Merge tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi
[linux-2.6-microblaze.git] / mm / ksm.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Memory merging support.
4  *
5  * This code enables dynamic sharing of identical pages found in different
6  * memory areas, even if they are not shared by fork()
7  *
8  * Copyright (C) 2008-2009 Red Hat, Inc.
9  * Authors:
10  *      Izik Eidus
11  *      Andrea Arcangeli
12  *      Chris Wright
13  *      Hugh Dickins
14  */
15
16 #include <linux/errno.h>
17 #include <linux/mm.h>
18 #include <linux/fs.h>
19 #include <linux/mman.h>
20 #include <linux/sched.h>
21 #include <linux/sched/mm.h>
22 #include <linux/sched/coredump.h>
23 #include <linux/rwsem.h>
24 #include <linux/pagemap.h>
25 #include <linux/rmap.h>
26 #include <linux/spinlock.h>
27 #include <linux/xxhash.h>
28 #include <linux/delay.h>
29 #include <linux/kthread.h>
30 #include <linux/wait.h>
31 #include <linux/slab.h>
32 #include <linux/rbtree.h>
33 #include <linux/memory.h>
34 #include <linux/mmu_notifier.h>
35 #include <linux/swap.h>
36 #include <linux/ksm.h>
37 #include <linux/hashtable.h>
38 #include <linux/freezer.h>
39 #include <linux/oom.h>
40 #include <linux/numa.h>
41
42 #include <asm/tlbflush.h>
43 #include "internal.h"
44
45 #ifdef CONFIG_NUMA
46 #define NUMA(x)         (x)
47 #define DO_NUMA(x)      do { (x); } while (0)
48 #else
49 #define NUMA(x)         (0)
50 #define DO_NUMA(x)      do { } while (0)
51 #endif
52
53 /**
54  * DOC: Overview
55  *
56  * A few notes about the KSM scanning process,
57  * to make it easier to understand the data structures below:
58  *
59  * In order to reduce excessive scanning, KSM sorts the memory pages by their
60  * contents into a data structure that holds pointers to the pages' locations.
61  *
62  * Since the contents of the pages may change at any moment, KSM cannot just
63  * insert the pages into a normal sorted tree and expect it to find anything.
64  * Therefore KSM uses two data structures - the stable and the unstable tree.
65  *
66  * The stable tree holds pointers to all the merged pages (ksm pages), sorted
67  * by their contents.  Because each such page is write-protected, searching on
68  * this tree is fully assured to be working (except when pages are unmapped),
69  * and therefore this tree is called the stable tree.
70  *
71  * The stable tree node includes information required for reverse
72  * mapping from a KSM page to virtual addresses that map this page.
73  *
74  * In order to avoid large latencies of the rmap walks on KSM pages,
75  * KSM maintains two types of nodes in the stable tree:
76  *
77  * * the regular nodes that keep the reverse mapping structures in a
78  *   linked list
79  * * the "chains" that link nodes ("dups") that represent the same
80  *   write protected memory content, but each "dup" corresponds to a
81  *   different KSM page copy of that content
82  *
83  * Internally, the regular nodes, "dups" and "chains" are represented
84  * using the same struct stable_node structure.
85  *
86  * In addition to the stable tree, KSM uses a second data structure called the
87  * unstable tree: this tree holds pointers to pages which have been found to
88  * be "unchanged for a period of time".  The unstable tree sorts these pages
89  * by their contents, but since they are not write-protected, KSM cannot rely
90  * upon the unstable tree to work correctly - the unstable tree is liable to
91  * be corrupted as its contents are modified, and so it is called unstable.
92  *
93  * KSM solves this problem by several techniques:
94  *
95  * 1) The unstable tree is flushed every time KSM completes scanning all
96  *    memory areas, and then the tree is rebuilt again from the beginning.
97  * 2) KSM will only insert into the unstable tree, pages whose hash value
98  *    has not changed since the previous scan of all memory areas.
99  * 3) The unstable tree is a RedBlack Tree - so its balancing is based on the
100  *    colors of the nodes and not on their contents, assuring that even when
101  *    the tree gets "corrupted" it won't get out of balance, so scanning time
102  *    remains the same (also, searching and inserting nodes in an rbtree uses
103  *    the same algorithm, so we have no overhead when we flush and rebuild).
104  * 4) KSM never flushes the stable tree, which means that even if it were to
105  *    take 10 attempts to find a page in the unstable tree, once it is found,
106  *    it is secured in the stable tree.  (When we scan a new page, we first
107  *    compare it against the stable tree, and then against the unstable tree.)
108  *
109  * If the merge_across_nodes tunable is unset, then KSM maintains multiple
110  * stable trees and multiple unstable trees: one of each for each NUMA node.
111  */
112
113 /**
114  * struct mm_slot - ksm information per mm that is being scanned
115  * @link: link to the mm_slots hash list
116  * @mm_list: link into the mm_slots list, rooted in ksm_mm_head
117  * @rmap_list: head for this mm_slot's singly-linked list of rmap_items
118  * @mm: the mm that this information is valid for
119  */
120 struct mm_slot {
121         struct hlist_node link;
122         struct list_head mm_list;
123         struct rmap_item *rmap_list;
124         struct mm_struct *mm;
125 };
126
127 /**
128  * struct ksm_scan - cursor for scanning
129  * @mm_slot: the current mm_slot we are scanning
130  * @address: the next address inside that to be scanned
131  * @rmap_list: link to the next rmap to be scanned in the rmap_list
132  * @seqnr: count of completed full scans (needed when removing unstable node)
133  *
134  * There is only the one ksm_scan instance of this cursor structure.
135  */
136 struct ksm_scan {
137         struct mm_slot *mm_slot;
138         unsigned long address;
139         struct rmap_item **rmap_list;
140         unsigned long seqnr;
141 };
142
143 /**
144  * struct stable_node - node of the stable rbtree
145  * @node: rb node of this ksm page in the stable tree
146  * @head: (overlaying parent) &migrate_nodes indicates temporarily on that list
147  * @hlist_dup: linked into the stable_node->hlist with a stable_node chain
148  * @list: linked into migrate_nodes, pending placement in the proper node tree
149  * @hlist: hlist head of rmap_items using this ksm page
150  * @kpfn: page frame number of this ksm page (perhaps temporarily on wrong nid)
151  * @chain_prune_time: time of the last full garbage collection
152  * @rmap_hlist_len: number of rmap_item entries in hlist or STABLE_NODE_CHAIN
153  * @nid: NUMA node id of stable tree in which linked (may not match kpfn)
154  */
155 struct stable_node {
156         union {
157                 struct rb_node node;    /* when node of stable tree */
158                 struct {                /* when listed for migration */
159                         struct list_head *head;
160                         struct {
161                                 struct hlist_node hlist_dup;
162                                 struct list_head list;
163                         };
164                 };
165         };
166         struct hlist_head hlist;
167         union {
168                 unsigned long kpfn;
169                 unsigned long chain_prune_time;
170         };
171         /*
172          * STABLE_NODE_CHAIN can be any negative number in
173          * rmap_hlist_len negative range, but better not -1 to be able
174          * to reliably detect underflows.
175          */
176 #define STABLE_NODE_CHAIN -1024
177         int rmap_hlist_len;
178 #ifdef CONFIG_NUMA
179         int nid;
180 #endif
181 };
182
183 /**
184  * struct rmap_item - reverse mapping item for virtual addresses
185  * @rmap_list: next rmap_item in mm_slot's singly-linked rmap_list
186  * @anon_vma: pointer to anon_vma for this mm,address, when in stable tree
187  * @nid: NUMA node id of unstable tree in which linked (may not match page)
188  * @mm: the memory structure this rmap_item is pointing into
189  * @address: the virtual address this rmap_item tracks (+ flags in low bits)
190  * @oldchecksum: previous checksum of the page at that virtual address
191  * @node: rb node of this rmap_item in the unstable tree
192  * @head: pointer to stable_node heading this list in the stable tree
193  * @hlist: link into hlist of rmap_items hanging off that stable_node
194  */
195 struct rmap_item {
196         struct rmap_item *rmap_list;
197         union {
198                 struct anon_vma *anon_vma;      /* when stable */
199 #ifdef CONFIG_NUMA
200                 int nid;                /* when node of unstable tree */
201 #endif
202         };
203         struct mm_struct *mm;
204         unsigned long address;          /* + low bits used for flags below */
205         unsigned int oldchecksum;       /* when unstable */
206         union {
207                 struct rb_node node;    /* when node of unstable tree */
208                 struct {                /* when listed from stable tree */
209                         struct stable_node *head;
210                         struct hlist_node hlist;
211                 };
212         };
213 };
214
215 #define SEQNR_MASK      0x0ff   /* low bits of unstable tree seqnr */
216 #define UNSTABLE_FLAG   0x100   /* is a node of the unstable tree */
217 #define STABLE_FLAG     0x200   /* is listed from the stable tree */
218 #define KSM_FLAG_MASK   (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG)
219                                 /* to mask all the flags */
220
221 /* The stable and unstable tree heads */
222 static struct rb_root one_stable_tree[1] = { RB_ROOT };
223 static struct rb_root one_unstable_tree[1] = { RB_ROOT };
224 static struct rb_root *root_stable_tree = one_stable_tree;
225 static struct rb_root *root_unstable_tree = one_unstable_tree;
226
227 /* Recently migrated nodes of stable tree, pending proper placement */
228 static LIST_HEAD(migrate_nodes);
229 #define STABLE_NODE_DUP_HEAD ((struct list_head *)&migrate_nodes.prev)
230
231 #define MM_SLOTS_HASH_BITS 10
232 static DEFINE_HASHTABLE(mm_slots_hash, MM_SLOTS_HASH_BITS);
233
234 static struct mm_slot ksm_mm_head = {
235         .mm_list = LIST_HEAD_INIT(ksm_mm_head.mm_list),
236 };
237 static struct ksm_scan ksm_scan = {
238         .mm_slot = &ksm_mm_head,
239 };
240
241 static struct kmem_cache *rmap_item_cache;
242 static struct kmem_cache *stable_node_cache;
243 static struct kmem_cache *mm_slot_cache;
244
245 /* The number of nodes in the stable tree */
246 static unsigned long ksm_pages_shared;
247
248 /* The number of page slots additionally sharing those nodes */
249 static unsigned long ksm_pages_sharing;
250
251 /* The number of nodes in the unstable tree */
252 static unsigned long ksm_pages_unshared;
253
254 /* The number of rmap_items in use: to calculate pages_volatile */
255 static unsigned long ksm_rmap_items;
256
257 /* The number of stable_node chains */
258 static unsigned long ksm_stable_node_chains;
259
260 /* The number of stable_node dups linked to the stable_node chains */
261 static unsigned long ksm_stable_node_dups;
262
263 /* Delay in pruning stale stable_node_dups in the stable_node_chains */
264 static int ksm_stable_node_chains_prune_millisecs = 2000;
265
266 /* Maximum number of page slots sharing a stable node */
267 static int ksm_max_page_sharing = 256;
268
269 /* Number of pages ksmd should scan in one batch */
270 static unsigned int ksm_thread_pages_to_scan = 100;
271
272 /* Milliseconds ksmd should sleep between batches */
273 static unsigned int ksm_thread_sleep_millisecs = 20;
274
275 /* Checksum of an empty (zeroed) page */
276 static unsigned int zero_checksum __read_mostly;
277
278 /* Whether to merge empty (zeroed) pages with actual zero pages */
279 static bool ksm_use_zero_pages __read_mostly;
280
281 #ifdef CONFIG_NUMA
282 /* Zeroed when merging across nodes is not allowed */
283 static unsigned int ksm_merge_across_nodes = 1;
284 static int ksm_nr_node_ids = 1;
285 #else
286 #define ksm_merge_across_nodes  1U
287 #define ksm_nr_node_ids         1
288 #endif
289
290 #define KSM_RUN_STOP    0
291 #define KSM_RUN_MERGE   1
292 #define KSM_RUN_UNMERGE 2
293 #define KSM_RUN_OFFLINE 4
294 static unsigned long ksm_run = KSM_RUN_STOP;
295 static void wait_while_offlining(void);
296
297 static DECLARE_WAIT_QUEUE_HEAD(ksm_thread_wait);
298 static DECLARE_WAIT_QUEUE_HEAD(ksm_iter_wait);
299 static DEFINE_MUTEX(ksm_thread_mutex);
300 static DEFINE_SPINLOCK(ksm_mmlist_lock);
301
302 #define KSM_KMEM_CACHE(__struct, __flags) kmem_cache_create("ksm_"#__struct,\
303                 sizeof(struct __struct), __alignof__(struct __struct),\
304                 (__flags), NULL)
305
306 static int __init ksm_slab_init(void)
307 {
308         rmap_item_cache = KSM_KMEM_CACHE(rmap_item, 0);
309         if (!rmap_item_cache)
310                 goto out;
311
312         stable_node_cache = KSM_KMEM_CACHE(stable_node, 0);
313         if (!stable_node_cache)
314                 goto out_free1;
315
316         mm_slot_cache = KSM_KMEM_CACHE(mm_slot, 0);
317         if (!mm_slot_cache)
318                 goto out_free2;
319
320         return 0;
321
322 out_free2:
323         kmem_cache_destroy(stable_node_cache);
324 out_free1:
325         kmem_cache_destroy(rmap_item_cache);
326 out:
327         return -ENOMEM;
328 }
329
330 static void __init ksm_slab_free(void)
331 {
332         kmem_cache_destroy(mm_slot_cache);
333         kmem_cache_destroy(stable_node_cache);
334         kmem_cache_destroy(rmap_item_cache);
335         mm_slot_cache = NULL;
336 }
337
338 static __always_inline bool is_stable_node_chain(struct stable_node *chain)
339 {
340         return chain->rmap_hlist_len == STABLE_NODE_CHAIN;
341 }
342
343 static __always_inline bool is_stable_node_dup(struct stable_node *dup)
344 {
345         return dup->head == STABLE_NODE_DUP_HEAD;
346 }
347
348 static inline void stable_node_chain_add_dup(struct stable_node *dup,
349                                              struct stable_node *chain)
350 {
351         VM_BUG_ON(is_stable_node_dup(dup));
352         dup->head = STABLE_NODE_DUP_HEAD;
353         VM_BUG_ON(!is_stable_node_chain(chain));
354         hlist_add_head(&dup->hlist_dup, &chain->hlist);
355         ksm_stable_node_dups++;
356 }
357
358 static inline void __stable_node_dup_del(struct stable_node *dup)
359 {
360         VM_BUG_ON(!is_stable_node_dup(dup));
361         hlist_del(&dup->hlist_dup);
362         ksm_stable_node_dups--;
363 }
364
365 static inline void stable_node_dup_del(struct stable_node *dup)
366 {
367         VM_BUG_ON(is_stable_node_chain(dup));
368         if (is_stable_node_dup(dup))
369                 __stable_node_dup_del(dup);
370         else
371                 rb_erase(&dup->node, root_stable_tree + NUMA(dup->nid));
372 #ifdef CONFIG_DEBUG_VM
373         dup->head = NULL;
374 #endif
375 }
376
377 static inline struct rmap_item *alloc_rmap_item(void)
378 {
379         struct rmap_item *rmap_item;
380
381         rmap_item = kmem_cache_zalloc(rmap_item_cache, GFP_KERNEL |
382                                                 __GFP_NORETRY | __GFP_NOWARN);
383         if (rmap_item)
384                 ksm_rmap_items++;
385         return rmap_item;
386 }
387
388 static inline void free_rmap_item(struct rmap_item *rmap_item)
389 {
390         ksm_rmap_items--;
391         rmap_item->mm = NULL;   /* debug safety */
392         kmem_cache_free(rmap_item_cache, rmap_item);
393 }
394
395 static inline struct stable_node *alloc_stable_node(void)
396 {
397         /*
398          * The allocation can take too long with GFP_KERNEL when memory is under
399          * pressure, which may lead to hung task warnings.  Adding __GFP_HIGH
400          * grants access to memory reserves, helping to avoid this problem.
401          */
402         return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
403 }
404
405 static inline void free_stable_node(struct stable_node *stable_node)
406 {
407         VM_BUG_ON(stable_node->rmap_hlist_len &&
408                   !is_stable_node_chain(stable_node));
409         kmem_cache_free(stable_node_cache, stable_node);
410 }
411
412 static inline struct mm_slot *alloc_mm_slot(void)
413 {
414         if (!mm_slot_cache)     /* initialization failed */
415                 return NULL;
416         return kmem_cache_zalloc(mm_slot_cache, GFP_KERNEL);
417 }
418
419 static inline void free_mm_slot(struct mm_slot *mm_slot)
420 {
421         kmem_cache_free(mm_slot_cache, mm_slot);
422 }
423
424 static struct mm_slot *get_mm_slot(struct mm_struct *mm)
425 {
426         struct mm_slot *slot;
427
428         hash_for_each_possible(mm_slots_hash, slot, link, (unsigned long)mm)
429                 if (slot->mm == mm)
430                         return slot;
431
432         return NULL;
433 }
434
435 static void insert_to_mm_slots_hash(struct mm_struct *mm,
436                                     struct mm_slot *mm_slot)
437 {
438         mm_slot->mm = mm;
439         hash_add(mm_slots_hash, &mm_slot->link, (unsigned long)mm);
440 }
441
442 /*
443  * ksmd, and unmerge_and_remove_all_rmap_items(), must not touch an mm's
444  * page tables after it has passed through ksm_exit() - which, if necessary,
445  * takes mmap_lock briefly to serialize against them.  ksm_exit() does not set
446  * a special flag: they can just back out as soon as mm_users goes to zero.
447  * ksm_test_exit() is used throughout to make this test for exit: in some
448  * places for correctness, in some places just to avoid unnecessary work.
449  */
450 static inline bool ksm_test_exit(struct mm_struct *mm)
451 {
452         return atomic_read(&mm->mm_users) == 0;
453 }
454
455 /*
456  * We use break_ksm to break COW on a ksm page: it's a stripped down
457  *
458  *      if (get_user_pages(addr, 1, FOLL_WRITE, &page, NULL) == 1)
459  *              put_page(page);
460  *
461  * but taking great care only to touch a ksm page, in a VM_MERGEABLE vma,
462  * in case the application has unmapped and remapped mm,addr meanwhile.
463  * Could a ksm page appear anywhere else?  Actually yes, in a VM_PFNMAP
464  * mmap of /dev/mem or /dev/kmem, where we would not want to touch it.
465  *
466  * FAULT_FLAG/FOLL_REMOTE are because we do this outside the context
467  * of the process that owns 'vma'.  We also do not want to enforce
468  * protection keys here anyway.
469  */
470 static int break_ksm(struct vm_area_struct *vma, unsigned long addr)
471 {
472         struct page *page;
473         vm_fault_t ret = 0;
474
475         do {
476                 cond_resched();
477                 page = follow_page(vma, addr,
478                                 FOLL_GET | FOLL_MIGRATION | FOLL_REMOTE);
479                 if (IS_ERR_OR_NULL(page))
480                         break;
481                 if (PageKsm(page))
482                         ret = handle_mm_fault(vma, addr,
483                                               FAULT_FLAG_WRITE | FAULT_FLAG_REMOTE,
484                                               NULL);
485                 else
486                         ret = VM_FAULT_WRITE;
487                 put_page(page);
488         } while (!(ret & (VM_FAULT_WRITE | VM_FAULT_SIGBUS | VM_FAULT_SIGSEGV | VM_FAULT_OOM)));
489         /*
490          * We must loop because handle_mm_fault() may back out if there's
491          * any difficulty e.g. if pte accessed bit gets updated concurrently.
492          *
493          * VM_FAULT_WRITE is what we have been hoping for: it indicates that
494          * COW has been broken, even if the vma does not permit VM_WRITE;
495          * but note that a concurrent fault might break PageKsm for us.
496          *
497          * VM_FAULT_SIGBUS could occur if we race with truncation of the
498          * backing file, which also invalidates anonymous pages: that's
499          * okay, that truncation will have unmapped the PageKsm for us.
500          *
501          * VM_FAULT_OOM: at the time of writing (late July 2009), setting
502          * aside mem_cgroup limits, VM_FAULT_OOM would only be set if the
503          * current task has TIF_MEMDIE set, and will be OOM killed on return
504          * to user; and ksmd, having no mm, would never be chosen for that.
505          *
506          * But if the mm is in a limited mem_cgroup, then the fault may fail
507          * with VM_FAULT_OOM even if the current task is not TIF_MEMDIE; and
508          * even ksmd can fail in this way - though it's usually breaking ksm
509          * just to undo a merge it made a moment before, so unlikely to oom.
510          *
511          * That's a pity: we might therefore have more kernel pages allocated
512          * than we're counting as nodes in the stable tree; but ksm_do_scan
513          * will retry to break_cow on each pass, so should recover the page
514          * in due course.  The important thing is to not let VM_MERGEABLE
515          * be cleared while any such pages might remain in the area.
516          */
517         return (ret & VM_FAULT_OOM) ? -ENOMEM : 0;
518 }
519
520 static struct vm_area_struct *find_mergeable_vma(struct mm_struct *mm,
521                 unsigned long addr)
522 {
523         struct vm_area_struct *vma;
524         if (ksm_test_exit(mm))
525                 return NULL;
526         vma = find_vma(mm, addr);
527         if (!vma || vma->vm_start > addr)
528                 return NULL;
529         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
530                 return NULL;
531         return vma;
532 }
533
534 static void break_cow(struct rmap_item *rmap_item)
535 {
536         struct mm_struct *mm = rmap_item->mm;
537         unsigned long addr = rmap_item->address;
538         struct vm_area_struct *vma;
539
540         /*
541          * It is not an accident that whenever we want to break COW
542          * to undo, we also need to drop a reference to the anon_vma.
543          */
544         put_anon_vma(rmap_item->anon_vma);
545
546         mmap_read_lock(mm);
547         vma = find_mergeable_vma(mm, addr);
548         if (vma)
549                 break_ksm(vma, addr);
550         mmap_read_unlock(mm);
551 }
552
553 static struct page *get_mergeable_page(struct rmap_item *rmap_item)
554 {
555         struct mm_struct *mm = rmap_item->mm;
556         unsigned long addr = rmap_item->address;
557         struct vm_area_struct *vma;
558         struct page *page;
559
560         mmap_read_lock(mm);
561         vma = find_mergeable_vma(mm, addr);
562         if (!vma)
563                 goto out;
564
565         page = follow_page(vma, addr, FOLL_GET);
566         if (IS_ERR_OR_NULL(page))
567                 goto out;
568         if (PageAnon(page)) {
569                 flush_anon_page(vma, page, addr);
570                 flush_dcache_page(page);
571         } else {
572                 put_page(page);
573 out:
574                 page = NULL;
575         }
576         mmap_read_unlock(mm);
577         return page;
578 }
579
580 /*
581  * This helper is used for getting right index into array of tree roots.
582  * When merge_across_nodes knob is set to 1, there are only two rb-trees for
583  * stable and unstable pages from all nodes with roots in index 0. Otherwise,
584  * every node has its own stable and unstable tree.
585  */
586 static inline int get_kpfn_nid(unsigned long kpfn)
587 {
588         return ksm_merge_across_nodes ? 0 : NUMA(pfn_to_nid(kpfn));
589 }
590
591 static struct stable_node *alloc_stable_node_chain(struct stable_node *dup,
592                                                    struct rb_root *root)
593 {
594         struct stable_node *chain = alloc_stable_node();
595         VM_BUG_ON(is_stable_node_chain(dup));
596         if (likely(chain)) {
597                 INIT_HLIST_HEAD(&chain->hlist);
598                 chain->chain_prune_time = jiffies;
599                 chain->rmap_hlist_len = STABLE_NODE_CHAIN;
600 #if defined (CONFIG_DEBUG_VM) && defined(CONFIG_NUMA)
601                 chain->nid = NUMA_NO_NODE; /* debug */
602 #endif
603                 ksm_stable_node_chains++;
604
605                 /*
606                  * Put the stable node chain in the first dimension of
607                  * the stable tree and at the same time remove the old
608                  * stable node.
609                  */
610                 rb_replace_node(&dup->node, &chain->node, root);
611
612                 /*
613                  * Move the old stable node to the second dimension
614                  * queued in the hlist_dup. The invariant is that all
615                  * dup stable_nodes in the chain->hlist point to pages
616                  * that are write protected and have the exact same
617                  * content.
618                  */
619                 stable_node_chain_add_dup(dup, chain);
620         }
621         return chain;
622 }
623
624 static inline void free_stable_node_chain(struct stable_node *chain,
625                                           struct rb_root *root)
626 {
627         rb_erase(&chain->node, root);
628         free_stable_node(chain);
629         ksm_stable_node_chains--;
630 }
631
632 static void remove_node_from_stable_tree(struct stable_node *stable_node)
633 {
634         struct rmap_item *rmap_item;
635
636         /* check it's not STABLE_NODE_CHAIN or negative */
637         BUG_ON(stable_node->rmap_hlist_len < 0);
638
639         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
640                 if (rmap_item->hlist.next)
641                         ksm_pages_sharing--;
642                 else
643                         ksm_pages_shared--;
644                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
645                 stable_node->rmap_hlist_len--;
646                 put_anon_vma(rmap_item->anon_vma);
647                 rmap_item->address &= PAGE_MASK;
648                 cond_resched();
649         }
650
651         /*
652          * We need the second aligned pointer of the migrate_nodes
653          * list_head to stay clear from the rb_parent_color union
654          * (aligned and different than any node) and also different
655          * from &migrate_nodes. This will verify that future list.h changes
656          * don't break STABLE_NODE_DUP_HEAD. Only recent gcc can handle it.
657          */
658 #if defined(GCC_VERSION) && GCC_VERSION >= 40903
659         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD <= &migrate_nodes);
660         BUILD_BUG_ON(STABLE_NODE_DUP_HEAD >= &migrate_nodes + 1);
661 #endif
662
663         if (stable_node->head == &migrate_nodes)
664                 list_del(&stable_node->list);
665         else
666                 stable_node_dup_del(stable_node);
667         free_stable_node(stable_node);
668 }
669
670 enum get_ksm_page_flags {
671         GET_KSM_PAGE_NOLOCK,
672         GET_KSM_PAGE_LOCK,
673         GET_KSM_PAGE_TRYLOCK
674 };
675
676 /*
677  * get_ksm_page: checks if the page indicated by the stable node
678  * is still its ksm page, despite having held no reference to it.
679  * In which case we can trust the content of the page, and it
680  * returns the gotten page; but if the page has now been zapped,
681  * remove the stale node from the stable tree and return NULL.
682  * But beware, the stable node's page might be being migrated.
683  *
684  * You would expect the stable_node to hold a reference to the ksm page.
685  * But if it increments the page's count, swapping out has to wait for
686  * ksmd to come around again before it can free the page, which may take
687  * seconds or even minutes: much too unresponsive.  So instead we use a
688  * "keyhole reference": access to the ksm page from the stable node peeps
689  * out through its keyhole to see if that page still holds the right key,
690  * pointing back to this stable node.  This relies on freeing a PageAnon
691  * page to reset its page->mapping to NULL, and relies on no other use of
692  * a page to put something that might look like our key in page->mapping.
693  * is on its way to being freed; but it is an anomaly to bear in mind.
694  */
695 static struct page *get_ksm_page(struct stable_node *stable_node,
696                                  enum get_ksm_page_flags flags)
697 {
698         struct page *page;
699         void *expected_mapping;
700         unsigned long kpfn;
701
702         expected_mapping = (void *)((unsigned long)stable_node |
703                                         PAGE_MAPPING_KSM);
704 again:
705         kpfn = READ_ONCE(stable_node->kpfn); /* Address dependency. */
706         page = pfn_to_page(kpfn);
707         if (READ_ONCE(page->mapping) != expected_mapping)
708                 goto stale;
709
710         /*
711          * We cannot do anything with the page while its refcount is 0.
712          * Usually 0 means free, or tail of a higher-order page: in which
713          * case this node is no longer referenced, and should be freed;
714          * however, it might mean that the page is under page_ref_freeze().
715          * The __remove_mapping() case is easy, again the node is now stale;
716          * the same is in reuse_ksm_page() case; but if page is swapcache
717          * in migrate_page_move_mapping(), it might still be our page,
718          * in which case it's essential to keep the node.
719          */
720         while (!get_page_unless_zero(page)) {
721                 /*
722                  * Another check for page->mapping != expected_mapping would
723                  * work here too.  We have chosen the !PageSwapCache test to
724                  * optimize the common case, when the page is or is about to
725                  * be freed: PageSwapCache is cleared (under spin_lock_irq)
726                  * in the ref_freeze section of __remove_mapping(); but Anon
727                  * page->mapping reset to NULL later, in free_pages_prepare().
728                  */
729                 if (!PageSwapCache(page))
730                         goto stale;
731                 cpu_relax();
732         }
733
734         if (READ_ONCE(page->mapping) != expected_mapping) {
735                 put_page(page);
736                 goto stale;
737         }
738
739         if (flags == GET_KSM_PAGE_TRYLOCK) {
740                 if (!trylock_page(page)) {
741                         put_page(page);
742                         return ERR_PTR(-EBUSY);
743                 }
744         } else if (flags == GET_KSM_PAGE_LOCK)
745                 lock_page(page);
746
747         if (flags != GET_KSM_PAGE_NOLOCK) {
748                 if (READ_ONCE(page->mapping) != expected_mapping) {
749                         unlock_page(page);
750                         put_page(page);
751                         goto stale;
752                 }
753         }
754         return page;
755
756 stale:
757         /*
758          * We come here from above when page->mapping or !PageSwapCache
759          * suggests that the node is stale; but it might be under migration.
760          * We need smp_rmb(), matching the smp_wmb() in ksm_migrate_page(),
761          * before checking whether node->kpfn has been changed.
762          */
763         smp_rmb();
764         if (READ_ONCE(stable_node->kpfn) != kpfn)
765                 goto again;
766         remove_node_from_stable_tree(stable_node);
767         return NULL;
768 }
769
770 /*
771  * Removing rmap_item from stable or unstable tree.
772  * This function will clean the information from the stable/unstable tree.
773  */
774 static void remove_rmap_item_from_tree(struct rmap_item *rmap_item)
775 {
776         if (rmap_item->address & STABLE_FLAG) {
777                 struct stable_node *stable_node;
778                 struct page *page;
779
780                 stable_node = rmap_item->head;
781                 page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
782                 if (!page)
783                         goto out;
784
785                 hlist_del(&rmap_item->hlist);
786                 unlock_page(page);
787                 put_page(page);
788
789                 if (!hlist_empty(&stable_node->hlist))
790                         ksm_pages_sharing--;
791                 else
792                         ksm_pages_shared--;
793                 VM_BUG_ON(stable_node->rmap_hlist_len <= 0);
794                 stable_node->rmap_hlist_len--;
795
796                 put_anon_vma(rmap_item->anon_vma);
797                 rmap_item->address &= PAGE_MASK;
798
799         } else if (rmap_item->address & UNSTABLE_FLAG) {
800                 unsigned char age;
801                 /*
802                  * Usually ksmd can and must skip the rb_erase, because
803                  * root_unstable_tree was already reset to RB_ROOT.
804                  * But be careful when an mm is exiting: do the rb_erase
805                  * if this rmap_item was inserted by this scan, rather
806                  * than left over from before.
807                  */
808                 age = (unsigned char)(ksm_scan.seqnr - rmap_item->address);
809                 BUG_ON(age > 1);
810                 if (!age)
811                         rb_erase(&rmap_item->node,
812                                  root_unstable_tree + NUMA(rmap_item->nid));
813                 ksm_pages_unshared--;
814                 rmap_item->address &= PAGE_MASK;
815         }
816 out:
817         cond_resched();         /* we're called from many long loops */
818 }
819
820 static void remove_trailing_rmap_items(struct mm_slot *mm_slot,
821                                        struct rmap_item **rmap_list)
822 {
823         while (*rmap_list) {
824                 struct rmap_item *rmap_item = *rmap_list;
825                 *rmap_list = rmap_item->rmap_list;
826                 remove_rmap_item_from_tree(rmap_item);
827                 free_rmap_item(rmap_item);
828         }
829 }
830
831 /*
832  * Though it's very tempting to unmerge rmap_items from stable tree rather
833  * than check every pte of a given vma, the locking doesn't quite work for
834  * that - an rmap_item is assigned to the stable tree after inserting ksm
835  * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
836  * rmap_items from parent to child at fork time (so as not to waste time
837  * if exit comes before the next scan reaches it).
838  *
839  * Similarly, although we'd like to remove rmap_items (so updating counts
840  * and freeing memory) when unmerging an area, it's easier to leave that
841  * to the next pass of ksmd - consider, for example, how ksmd might be
842  * in cmp_and_merge_page on one of the rmap_items we would be removing.
843  */
844 static int unmerge_ksm_pages(struct vm_area_struct *vma,
845                              unsigned long start, unsigned long end)
846 {
847         unsigned long addr;
848         int err = 0;
849
850         for (addr = start; addr < end && !err; addr += PAGE_SIZE) {
851                 if (ksm_test_exit(vma->vm_mm))
852                         break;
853                 if (signal_pending(current))
854                         err = -ERESTARTSYS;
855                 else
856                         err = break_ksm(vma, addr);
857         }
858         return err;
859 }
860
861 static inline struct stable_node *page_stable_node(struct page *page)
862 {
863         return PageKsm(page) ? page_rmapping(page) : NULL;
864 }
865
866 static inline void set_page_stable_node(struct page *page,
867                                         struct stable_node *stable_node)
868 {
869         page->mapping = (void *)((unsigned long)stable_node | PAGE_MAPPING_KSM);
870 }
871
872 #ifdef CONFIG_SYSFS
873 /*
874  * Only called through the sysfs control interface:
875  */
876 static int remove_stable_node(struct stable_node *stable_node)
877 {
878         struct page *page;
879         int err;
880
881         page = get_ksm_page(stable_node, GET_KSM_PAGE_LOCK);
882         if (!page) {
883                 /*
884                  * get_ksm_page did remove_node_from_stable_tree itself.
885                  */
886                 return 0;
887         }
888
889         /*
890          * Page could be still mapped if this races with __mmput() running in
891          * between ksm_exit() and exit_mmap(). Just refuse to let
892          * merge_across_nodes/max_page_sharing be switched.
893          */
894         err = -EBUSY;
895         if (!page_mapped(page)) {
896                 /*
897                  * The stable node did not yet appear stale to get_ksm_page(),
898                  * since that allows for an unmapped ksm page to be recognized
899                  * right up until it is freed; but the node is safe to remove.
900                  * This page might be in a pagevec waiting to be freed,
901                  * or it might be PageSwapCache (perhaps under writeback),
902                  * or it might have been removed from swapcache a moment ago.
903                  */
904                 set_page_stable_node(page, NULL);
905                 remove_node_from_stable_tree(stable_node);
906                 err = 0;
907         }
908
909         unlock_page(page);
910         put_page(page);
911         return err;
912 }
913
914 static int remove_stable_node_chain(struct stable_node *stable_node,
915                                     struct rb_root *root)
916 {
917         struct stable_node *dup;
918         struct hlist_node *hlist_safe;
919
920         if (!is_stable_node_chain(stable_node)) {
921                 VM_BUG_ON(is_stable_node_dup(stable_node));
922                 if (remove_stable_node(stable_node))
923                         return true;
924                 else
925                         return false;
926         }
927
928         hlist_for_each_entry_safe(dup, hlist_safe,
929                                   &stable_node->hlist, hlist_dup) {
930                 VM_BUG_ON(!is_stable_node_dup(dup));
931                 if (remove_stable_node(dup))
932                         return true;
933         }
934         BUG_ON(!hlist_empty(&stable_node->hlist));
935         free_stable_node_chain(stable_node, root);
936         return false;
937 }
938
939 static int remove_all_stable_nodes(void)
940 {
941         struct stable_node *stable_node, *next;
942         int nid;
943         int err = 0;
944
945         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
946                 while (root_stable_tree[nid].rb_node) {
947                         stable_node = rb_entry(root_stable_tree[nid].rb_node,
948                                                 struct stable_node, node);
949                         if (remove_stable_node_chain(stable_node,
950                                                      root_stable_tree + nid)) {
951                                 err = -EBUSY;
952                                 break;  /* proceed to next nid */
953                         }
954                         cond_resched();
955                 }
956         }
957         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
958                 if (remove_stable_node(stable_node))
959                         err = -EBUSY;
960                 cond_resched();
961         }
962         return err;
963 }
964
965 static int unmerge_and_remove_all_rmap_items(void)
966 {
967         struct mm_slot *mm_slot;
968         struct mm_struct *mm;
969         struct vm_area_struct *vma;
970         int err = 0;
971
972         spin_lock(&ksm_mmlist_lock);
973         ksm_scan.mm_slot = list_entry(ksm_mm_head.mm_list.next,
974                                                 struct mm_slot, mm_list);
975         spin_unlock(&ksm_mmlist_lock);
976
977         for (mm_slot = ksm_scan.mm_slot;
978                         mm_slot != &ksm_mm_head; mm_slot = ksm_scan.mm_slot) {
979                 mm = mm_slot->mm;
980                 mmap_read_lock(mm);
981                 for (vma = mm->mmap; vma; vma = vma->vm_next) {
982                         if (ksm_test_exit(mm))
983                                 break;
984                         if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
985                                 continue;
986                         err = unmerge_ksm_pages(vma,
987                                                 vma->vm_start, vma->vm_end);
988                         if (err)
989                                 goto error;
990                 }
991
992                 remove_trailing_rmap_items(mm_slot, &mm_slot->rmap_list);
993                 mmap_read_unlock(mm);
994
995                 spin_lock(&ksm_mmlist_lock);
996                 ksm_scan.mm_slot = list_entry(mm_slot->mm_list.next,
997                                                 struct mm_slot, mm_list);
998                 if (ksm_test_exit(mm)) {
999                         hash_del(&mm_slot->link);
1000                         list_del(&mm_slot->mm_list);
1001                         spin_unlock(&ksm_mmlist_lock);
1002
1003                         free_mm_slot(mm_slot);
1004                         clear_bit(MMF_VM_MERGEABLE, &mm->flags);
1005                         mmdrop(mm);
1006                 } else
1007                         spin_unlock(&ksm_mmlist_lock);
1008         }
1009
1010         /* Clean up stable nodes, but don't worry if some are still busy */
1011         remove_all_stable_nodes();
1012         ksm_scan.seqnr = 0;
1013         return 0;
1014
1015 error:
1016         mmap_read_unlock(mm);
1017         spin_lock(&ksm_mmlist_lock);
1018         ksm_scan.mm_slot = &ksm_mm_head;
1019         spin_unlock(&ksm_mmlist_lock);
1020         return err;
1021 }
1022 #endif /* CONFIG_SYSFS */
1023
1024 static u32 calc_checksum(struct page *page)
1025 {
1026         u32 checksum;
1027         void *addr = kmap_atomic(page);
1028         checksum = xxhash(addr, PAGE_SIZE, 0);
1029         kunmap_atomic(addr);
1030         return checksum;
1031 }
1032
1033 static int write_protect_page(struct vm_area_struct *vma, struct page *page,
1034                               pte_t *orig_pte)
1035 {
1036         struct mm_struct *mm = vma->vm_mm;
1037         struct page_vma_mapped_walk pvmw = {
1038                 .page = page,
1039                 .vma = vma,
1040         };
1041         int swapped;
1042         int err = -EFAULT;
1043         struct mmu_notifier_range range;
1044
1045         pvmw.address = page_address_in_vma(page, vma);
1046         if (pvmw.address == -EFAULT)
1047                 goto out;
1048
1049         BUG_ON(PageTransCompound(page));
1050
1051         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm,
1052                                 pvmw.address,
1053                                 pvmw.address + PAGE_SIZE);
1054         mmu_notifier_invalidate_range_start(&range);
1055
1056         if (!page_vma_mapped_walk(&pvmw))
1057                 goto out_mn;
1058         if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
1059                 goto out_unlock;
1060
1061         if (pte_write(*pvmw.pte) || pte_dirty(*pvmw.pte) ||
1062             (pte_protnone(*pvmw.pte) && pte_savedwrite(*pvmw.pte)) ||
1063                                                 mm_tlb_flush_pending(mm)) {
1064                 pte_t entry;
1065
1066                 swapped = PageSwapCache(page);
1067                 flush_cache_page(vma, pvmw.address, page_to_pfn(page));
1068                 /*
1069                  * Ok this is tricky, when get_user_pages_fast() run it doesn't
1070                  * take any lock, therefore the check that we are going to make
1071                  * with the pagecount against the mapcount is racey and
1072                  * O_DIRECT can happen right after the check.
1073                  * So we clear the pte and flush the tlb before the check
1074                  * this assure us that no O_DIRECT can happen after the check
1075                  * or in the middle of the check.
1076                  *
1077                  * No need to notify as we are downgrading page table to read
1078                  * only not changing it to point to a new page.
1079                  *
1080                  * See Documentation/vm/mmu_notifier.rst
1081                  */
1082                 entry = ptep_clear_flush(vma, pvmw.address, pvmw.pte);
1083                 /*
1084                  * Check that no O_DIRECT or similar I/O is in progress on the
1085                  * page
1086                  */
1087                 if (page_mapcount(page) + 1 + swapped != page_count(page)) {
1088                         set_pte_at(mm, pvmw.address, pvmw.pte, entry);
1089                         goto out_unlock;
1090                 }
1091                 if (pte_dirty(entry))
1092                         set_page_dirty(page);
1093
1094                 if (pte_protnone(entry))
1095                         entry = pte_mkclean(pte_clear_savedwrite(entry));
1096                 else
1097                         entry = pte_mkclean(pte_wrprotect(entry));
1098                 set_pte_at_notify(mm, pvmw.address, pvmw.pte, entry);
1099         }
1100         *orig_pte = *pvmw.pte;
1101         err = 0;
1102
1103 out_unlock:
1104         page_vma_mapped_walk_done(&pvmw);
1105 out_mn:
1106         mmu_notifier_invalidate_range_end(&range);
1107 out:
1108         return err;
1109 }
1110
1111 /**
1112  * replace_page - replace page in vma by new ksm page
1113  * @vma:      vma that holds the pte pointing to page
1114  * @page:     the page we are replacing by kpage
1115  * @kpage:    the ksm page we replace page by
1116  * @orig_pte: the original value of the pte
1117  *
1118  * Returns 0 on success, -EFAULT on failure.
1119  */
1120 static int replace_page(struct vm_area_struct *vma, struct page *page,
1121                         struct page *kpage, pte_t orig_pte)
1122 {
1123         struct mm_struct *mm = vma->vm_mm;
1124         pmd_t *pmd;
1125         pte_t *ptep;
1126         pte_t newpte;
1127         spinlock_t *ptl;
1128         unsigned long addr;
1129         int err = -EFAULT;
1130         struct mmu_notifier_range range;
1131
1132         addr = page_address_in_vma(page, vma);
1133         if (addr == -EFAULT)
1134                 goto out;
1135
1136         pmd = mm_find_pmd(mm, addr);
1137         if (!pmd)
1138                 goto out;
1139
1140         mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
1141                                 addr + PAGE_SIZE);
1142         mmu_notifier_invalidate_range_start(&range);
1143
1144         ptep = pte_offset_map_lock(mm, pmd, addr, &ptl);
1145         if (!pte_same(*ptep, orig_pte)) {
1146                 pte_unmap_unlock(ptep, ptl);
1147                 goto out_mn;
1148         }
1149
1150         /*
1151          * No need to check ksm_use_zero_pages here: we can only have a
1152          * zero_page here if ksm_use_zero_pages was enabled already.
1153          */
1154         if (!is_zero_pfn(page_to_pfn(kpage))) {
1155                 get_page(kpage);
1156                 page_add_anon_rmap(kpage, vma, addr, false);
1157                 newpte = mk_pte(kpage, vma->vm_page_prot);
1158         } else {
1159                 newpte = pte_mkspecial(pfn_pte(page_to_pfn(kpage),
1160                                                vma->vm_page_prot));
1161                 /*
1162                  * We're replacing an anonymous page with a zero page, which is
1163                  * not anonymous. We need to do proper accounting otherwise we
1164                  * will get wrong values in /proc, and a BUG message in dmesg
1165                  * when tearing down the mm.
1166                  */
1167                 dec_mm_counter(mm, MM_ANONPAGES);
1168         }
1169
1170         flush_cache_page(vma, addr, pte_pfn(*ptep));
1171         /*
1172          * No need to notify as we are replacing a read only page with another
1173          * read only page with the same content.
1174          *
1175          * See Documentation/vm/mmu_notifier.rst
1176          */
1177         ptep_clear_flush(vma, addr, ptep);
1178         set_pte_at_notify(mm, addr, ptep, newpte);
1179
1180         page_remove_rmap(page, false);
1181         if (!page_mapped(page))
1182                 try_to_free_swap(page);
1183         put_page(page);
1184
1185         pte_unmap_unlock(ptep, ptl);
1186         err = 0;
1187 out_mn:
1188         mmu_notifier_invalidate_range_end(&range);
1189 out:
1190         return err;
1191 }
1192
1193 /*
1194  * try_to_merge_one_page - take two pages and merge them into one
1195  * @vma: the vma that holds the pte pointing to page
1196  * @page: the PageAnon page that we want to replace with kpage
1197  * @kpage: the PageKsm page that we want to map instead of page,
1198  *         or NULL the first time when we want to use page as kpage.
1199  *
1200  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1201  */
1202 static int try_to_merge_one_page(struct vm_area_struct *vma,
1203                                  struct page *page, struct page *kpage)
1204 {
1205         pte_t orig_pte = __pte(0);
1206         int err = -EFAULT;
1207
1208         if (page == kpage)                      /* ksm page forked */
1209                 return 0;
1210
1211         if (!PageAnon(page))
1212                 goto out;
1213
1214         /*
1215          * We need the page lock to read a stable PageSwapCache in
1216          * write_protect_page().  We use trylock_page() instead of
1217          * lock_page() because we don't want to wait here - we
1218          * prefer to continue scanning and merging different pages,
1219          * then come back to this page when it is unlocked.
1220          */
1221         if (!trylock_page(page))
1222                 goto out;
1223
1224         if (PageTransCompound(page)) {
1225                 if (split_huge_page(page))
1226                         goto out_unlock;
1227         }
1228
1229         /*
1230          * If this anonymous page is mapped only here, its pte may need
1231          * to be write-protected.  If it's mapped elsewhere, all of its
1232          * ptes are necessarily already write-protected.  But in either
1233          * case, we need to lock and check page_count is not raised.
1234          */
1235         if (write_protect_page(vma, page, &orig_pte) == 0) {
1236                 if (!kpage) {
1237                         /*
1238                          * While we hold page lock, upgrade page from
1239                          * PageAnon+anon_vma to PageKsm+NULL stable_node:
1240                          * stable_tree_insert() will update stable_node.
1241                          */
1242                         set_page_stable_node(page, NULL);
1243                         mark_page_accessed(page);
1244                         /*
1245                          * Page reclaim just frees a clean page with no dirty
1246                          * ptes: make sure that the ksm page would be swapped.
1247                          */
1248                         if (!PageDirty(page))
1249                                 SetPageDirty(page);
1250                         err = 0;
1251                 } else if (pages_identical(page, kpage))
1252                         err = replace_page(vma, page, kpage, orig_pte);
1253         }
1254
1255         if ((vma->vm_flags & VM_LOCKED) && kpage && !err) {
1256                 munlock_vma_page(page);
1257                 if (!PageMlocked(kpage)) {
1258                         unlock_page(page);
1259                         lock_page(kpage);
1260                         mlock_vma_page(kpage);
1261                         page = kpage;           /* for final unlock */
1262                 }
1263         }
1264
1265 out_unlock:
1266         unlock_page(page);
1267 out:
1268         return err;
1269 }
1270
1271 /*
1272  * try_to_merge_with_ksm_page - like try_to_merge_two_pages,
1273  * but no new kernel page is allocated: kpage must already be a ksm page.
1274  *
1275  * This function returns 0 if the pages were merged, -EFAULT otherwise.
1276  */
1277 static int try_to_merge_with_ksm_page(struct rmap_item *rmap_item,
1278                                       struct page *page, struct page *kpage)
1279 {
1280         struct mm_struct *mm = rmap_item->mm;
1281         struct vm_area_struct *vma;
1282         int err = -EFAULT;
1283
1284         mmap_read_lock(mm);
1285         vma = find_mergeable_vma(mm, rmap_item->address);
1286         if (!vma)
1287                 goto out;
1288
1289         err = try_to_merge_one_page(vma, page, kpage);
1290         if (err)
1291                 goto out;
1292
1293         /* Unstable nid is in union with stable anon_vma: remove first */
1294         remove_rmap_item_from_tree(rmap_item);
1295
1296         /* Must get reference to anon_vma while still holding mmap_lock */
1297         rmap_item->anon_vma = vma->anon_vma;
1298         get_anon_vma(vma->anon_vma);
1299 out:
1300         mmap_read_unlock(mm);
1301         return err;
1302 }
1303
1304 /*
1305  * try_to_merge_two_pages - take two identical pages and prepare them
1306  * to be merged into one page.
1307  *
1308  * This function returns the kpage if we successfully merged two identical
1309  * pages into one ksm page, NULL otherwise.
1310  *
1311  * Note that this function upgrades page to ksm page: if one of the pages
1312  * is already a ksm page, try_to_merge_with_ksm_page should be used.
1313  */
1314 static struct page *try_to_merge_two_pages(struct rmap_item *rmap_item,
1315                                            struct page *page,
1316                                            struct rmap_item *tree_rmap_item,
1317                                            struct page *tree_page)
1318 {
1319         int err;
1320
1321         err = try_to_merge_with_ksm_page(rmap_item, page, NULL);
1322         if (!err) {
1323                 err = try_to_merge_with_ksm_page(tree_rmap_item,
1324                                                         tree_page, page);
1325                 /*
1326                  * If that fails, we have a ksm page with only one pte
1327                  * pointing to it: so break it.
1328                  */
1329                 if (err)
1330                         break_cow(rmap_item);
1331         }
1332         return err ? NULL : page;
1333 }
1334
1335 static __always_inline
1336 bool __is_page_sharing_candidate(struct stable_node *stable_node, int offset)
1337 {
1338         VM_BUG_ON(stable_node->rmap_hlist_len < 0);
1339         /*
1340          * Check that at least one mapping still exists, otherwise
1341          * there's no much point to merge and share with this
1342          * stable_node, as the underlying tree_page of the other
1343          * sharer is going to be freed soon.
1344          */
1345         return stable_node->rmap_hlist_len &&
1346                 stable_node->rmap_hlist_len + offset < ksm_max_page_sharing;
1347 }
1348
1349 static __always_inline
1350 bool is_page_sharing_candidate(struct stable_node *stable_node)
1351 {
1352         return __is_page_sharing_candidate(stable_node, 0);
1353 }
1354
1355 static struct page *stable_node_dup(struct stable_node **_stable_node_dup,
1356                                     struct stable_node **_stable_node,
1357                                     struct rb_root *root,
1358                                     bool prune_stale_stable_nodes)
1359 {
1360         struct stable_node *dup, *found = NULL, *stable_node = *_stable_node;
1361         struct hlist_node *hlist_safe;
1362         struct page *_tree_page, *tree_page = NULL;
1363         int nr = 0;
1364         int found_rmap_hlist_len;
1365
1366         if (!prune_stale_stable_nodes ||
1367             time_before(jiffies, stable_node->chain_prune_time +
1368                         msecs_to_jiffies(
1369                                 ksm_stable_node_chains_prune_millisecs)))
1370                 prune_stale_stable_nodes = false;
1371         else
1372                 stable_node->chain_prune_time = jiffies;
1373
1374         hlist_for_each_entry_safe(dup, hlist_safe,
1375                                   &stable_node->hlist, hlist_dup) {
1376                 cond_resched();
1377                 /*
1378                  * We must walk all stable_node_dup to prune the stale
1379                  * stable nodes during lookup.
1380                  *
1381                  * get_ksm_page can drop the nodes from the
1382                  * stable_node->hlist if they point to freed pages
1383                  * (that's why we do a _safe walk). The "dup"
1384                  * stable_node parameter itself will be freed from
1385                  * under us if it returns NULL.
1386                  */
1387                 _tree_page = get_ksm_page(dup, GET_KSM_PAGE_NOLOCK);
1388                 if (!_tree_page)
1389                         continue;
1390                 nr += 1;
1391                 if (is_page_sharing_candidate(dup)) {
1392                         if (!found ||
1393                             dup->rmap_hlist_len > found_rmap_hlist_len) {
1394                                 if (found)
1395                                         put_page(tree_page);
1396                                 found = dup;
1397                                 found_rmap_hlist_len = found->rmap_hlist_len;
1398                                 tree_page = _tree_page;
1399
1400                                 /* skip put_page for found dup */
1401                                 if (!prune_stale_stable_nodes)
1402                                         break;
1403                                 continue;
1404                         }
1405                 }
1406                 put_page(_tree_page);
1407         }
1408
1409         if (found) {
1410                 /*
1411                  * nr is counting all dups in the chain only if
1412                  * prune_stale_stable_nodes is true, otherwise we may
1413                  * break the loop at nr == 1 even if there are
1414                  * multiple entries.
1415                  */
1416                 if (prune_stale_stable_nodes && nr == 1) {
1417                         /*
1418                          * If there's not just one entry it would
1419                          * corrupt memory, better BUG_ON. In KSM
1420                          * context with no lock held it's not even
1421                          * fatal.
1422                          */
1423                         BUG_ON(stable_node->hlist.first->next);
1424
1425                         /*
1426                          * There's just one entry and it is below the
1427                          * deduplication limit so drop the chain.
1428                          */
1429                         rb_replace_node(&stable_node->node, &found->node,
1430                                         root);
1431                         free_stable_node(stable_node);
1432                         ksm_stable_node_chains--;
1433                         ksm_stable_node_dups--;
1434                         /*
1435                          * NOTE: the caller depends on the stable_node
1436                          * to be equal to stable_node_dup if the chain
1437                          * was collapsed.
1438                          */
1439                         *_stable_node = found;
1440                         /*
1441                          * Just for robustneess as stable_node is
1442                          * otherwise left as a stable pointer, the
1443                          * compiler shall optimize it away at build
1444                          * time.
1445                          */
1446                         stable_node = NULL;
1447                 } else if (stable_node->hlist.first != &found->hlist_dup &&
1448                            __is_page_sharing_candidate(found, 1)) {
1449                         /*
1450                          * If the found stable_node dup can accept one
1451                          * more future merge (in addition to the one
1452                          * that is underway) and is not at the head of
1453                          * the chain, put it there so next search will
1454                          * be quicker in the !prune_stale_stable_nodes
1455                          * case.
1456                          *
1457                          * NOTE: it would be inaccurate to use nr > 1
1458                          * instead of checking the hlist.first pointer
1459                          * directly, because in the
1460                          * prune_stale_stable_nodes case "nr" isn't
1461                          * the position of the found dup in the chain,
1462                          * but the total number of dups in the chain.
1463                          */
1464                         hlist_del(&found->hlist_dup);
1465                         hlist_add_head(&found->hlist_dup,
1466                                        &stable_node->hlist);
1467                 }
1468         }
1469
1470         *_stable_node_dup = found;
1471         return tree_page;
1472 }
1473
1474 static struct stable_node *stable_node_dup_any(struct stable_node *stable_node,
1475                                                struct rb_root *root)
1476 {
1477         if (!is_stable_node_chain(stable_node))
1478                 return stable_node;
1479         if (hlist_empty(&stable_node->hlist)) {
1480                 free_stable_node_chain(stable_node, root);
1481                 return NULL;
1482         }
1483         return hlist_entry(stable_node->hlist.first,
1484                            typeof(*stable_node), hlist_dup);
1485 }
1486
1487 /*
1488  * Like for get_ksm_page, this function can free the *_stable_node and
1489  * *_stable_node_dup if the returned tree_page is NULL.
1490  *
1491  * It can also free and overwrite *_stable_node with the found
1492  * stable_node_dup if the chain is collapsed (in which case
1493  * *_stable_node will be equal to *_stable_node_dup like if the chain
1494  * never existed). It's up to the caller to verify tree_page is not
1495  * NULL before dereferencing *_stable_node or *_stable_node_dup.
1496  *
1497  * *_stable_node_dup is really a second output parameter of this
1498  * function and will be overwritten in all cases, the caller doesn't
1499  * need to initialize it.
1500  */
1501 static struct page *__stable_node_chain(struct stable_node **_stable_node_dup,
1502                                         struct stable_node **_stable_node,
1503                                         struct rb_root *root,
1504                                         bool prune_stale_stable_nodes)
1505 {
1506         struct stable_node *stable_node = *_stable_node;
1507         if (!is_stable_node_chain(stable_node)) {
1508                 if (is_page_sharing_candidate(stable_node)) {
1509                         *_stable_node_dup = stable_node;
1510                         return get_ksm_page(stable_node, GET_KSM_PAGE_NOLOCK);
1511                 }
1512                 /*
1513                  * _stable_node_dup set to NULL means the stable_node
1514                  * reached the ksm_max_page_sharing limit.
1515                  */
1516                 *_stable_node_dup = NULL;
1517                 return NULL;
1518         }
1519         return stable_node_dup(_stable_node_dup, _stable_node, root,
1520                                prune_stale_stable_nodes);
1521 }
1522
1523 static __always_inline struct page *chain_prune(struct stable_node **s_n_d,
1524                                                 struct stable_node **s_n,
1525                                                 struct rb_root *root)
1526 {
1527         return __stable_node_chain(s_n_d, s_n, root, true);
1528 }
1529
1530 static __always_inline struct page *chain(struct stable_node **s_n_d,
1531                                           struct stable_node *s_n,
1532                                           struct rb_root *root)
1533 {
1534         struct stable_node *old_stable_node = s_n;
1535         struct page *tree_page;
1536
1537         tree_page = __stable_node_chain(s_n_d, &s_n, root, false);
1538         /* not pruning dups so s_n cannot have changed */
1539         VM_BUG_ON(s_n != old_stable_node);
1540         return tree_page;
1541 }
1542
1543 /*
1544  * stable_tree_search - search for page inside the stable tree
1545  *
1546  * This function checks if there is a page inside the stable tree
1547  * with identical content to the page that we are scanning right now.
1548  *
1549  * This function returns the stable tree node of identical content if found,
1550  * NULL otherwise.
1551  */
1552 static struct page *stable_tree_search(struct page *page)
1553 {
1554         int nid;
1555         struct rb_root *root;
1556         struct rb_node **new;
1557         struct rb_node *parent;
1558         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1559         struct stable_node *page_node;
1560
1561         page_node = page_stable_node(page);
1562         if (page_node && page_node->head != &migrate_nodes) {
1563                 /* ksm page forked */
1564                 get_page(page);
1565                 return page;
1566         }
1567
1568         nid = get_kpfn_nid(page_to_pfn(page));
1569         root = root_stable_tree + nid;
1570 again:
1571         new = &root->rb_node;
1572         parent = NULL;
1573
1574         while (*new) {
1575                 struct page *tree_page;
1576                 int ret;
1577
1578                 cond_resched();
1579                 stable_node = rb_entry(*new, struct stable_node, node);
1580                 stable_node_any = NULL;
1581                 tree_page = chain_prune(&stable_node_dup, &stable_node, root);
1582                 /*
1583                  * NOTE: stable_node may have been freed by
1584                  * chain_prune() if the returned stable_node_dup is
1585                  * not NULL. stable_node_dup may have been inserted in
1586                  * the rbtree instead as a regular stable_node (in
1587                  * order to collapse the stable_node chain if a single
1588                  * stable_node dup was found in it). In such case the
1589                  * stable_node is overwritten by the calleee to point
1590                  * to the stable_node_dup that was collapsed in the
1591                  * stable rbtree and stable_node will be equal to
1592                  * stable_node_dup like if the chain never existed.
1593                  */
1594                 if (!stable_node_dup) {
1595                         /*
1596                          * Either all stable_node dups were full in
1597                          * this stable_node chain, or this chain was
1598                          * empty and should be rb_erased.
1599                          */
1600                         stable_node_any = stable_node_dup_any(stable_node,
1601                                                               root);
1602                         if (!stable_node_any) {
1603                                 /* rb_erase just run */
1604                                 goto again;
1605                         }
1606                         /*
1607                          * Take any of the stable_node dups page of
1608                          * this stable_node chain to let the tree walk
1609                          * continue. All KSM pages belonging to the
1610                          * stable_node dups in a stable_node chain
1611                          * have the same content and they're
1612                          * write protected at all times. Any will work
1613                          * fine to continue the walk.
1614                          */
1615                         tree_page = get_ksm_page(stable_node_any,
1616                                                  GET_KSM_PAGE_NOLOCK);
1617                 }
1618                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1619                 if (!tree_page) {
1620                         /*
1621                          * If we walked over a stale stable_node,
1622                          * get_ksm_page() will call rb_erase() and it
1623                          * may rebalance the tree from under us. So
1624                          * restart the search from scratch. Returning
1625                          * NULL would be safe too, but we'd generate
1626                          * false negative insertions just because some
1627                          * stable_node was stale.
1628                          */
1629                         goto again;
1630                 }
1631
1632                 ret = memcmp_pages(page, tree_page);
1633                 put_page(tree_page);
1634
1635                 parent = *new;
1636                 if (ret < 0)
1637                         new = &parent->rb_left;
1638                 else if (ret > 0)
1639                         new = &parent->rb_right;
1640                 else {
1641                         if (page_node) {
1642                                 VM_BUG_ON(page_node->head != &migrate_nodes);
1643                                 /*
1644                                  * Test if the migrated page should be merged
1645                                  * into a stable node dup. If the mapcount is
1646                                  * 1 we can migrate it with another KSM page
1647                                  * without adding it to the chain.
1648                                  */
1649                                 if (page_mapcount(page) > 1)
1650                                         goto chain_append;
1651                         }
1652
1653                         if (!stable_node_dup) {
1654                                 /*
1655                                  * If the stable_node is a chain and
1656                                  * we got a payload match in memcmp
1657                                  * but we cannot merge the scanned
1658                                  * page in any of the existing
1659                                  * stable_node dups because they're
1660                                  * all full, we need to wait the
1661                                  * scanned page to find itself a match
1662                                  * in the unstable tree to create a
1663                                  * brand new KSM page to add later to
1664                                  * the dups of this stable_node.
1665                                  */
1666                                 return NULL;
1667                         }
1668
1669                         /*
1670                          * Lock and unlock the stable_node's page (which
1671                          * might already have been migrated) so that page
1672                          * migration is sure to notice its raised count.
1673                          * It would be more elegant to return stable_node
1674                          * than kpage, but that involves more changes.
1675                          */
1676                         tree_page = get_ksm_page(stable_node_dup,
1677                                                  GET_KSM_PAGE_TRYLOCK);
1678
1679                         if (PTR_ERR(tree_page) == -EBUSY)
1680                                 return ERR_PTR(-EBUSY);
1681
1682                         if (unlikely(!tree_page))
1683                                 /*
1684                                  * The tree may have been rebalanced,
1685                                  * so re-evaluate parent and new.
1686                                  */
1687                                 goto again;
1688                         unlock_page(tree_page);
1689
1690                         if (get_kpfn_nid(stable_node_dup->kpfn) !=
1691                             NUMA(stable_node_dup->nid)) {
1692                                 put_page(tree_page);
1693                                 goto replace;
1694                         }
1695                         return tree_page;
1696                 }
1697         }
1698
1699         if (!page_node)
1700                 return NULL;
1701
1702         list_del(&page_node->list);
1703         DO_NUMA(page_node->nid = nid);
1704         rb_link_node(&page_node->node, parent, new);
1705         rb_insert_color(&page_node->node, root);
1706 out:
1707         if (is_page_sharing_candidate(page_node)) {
1708                 get_page(page);
1709                 return page;
1710         } else
1711                 return NULL;
1712
1713 replace:
1714         /*
1715          * If stable_node was a chain and chain_prune collapsed it,
1716          * stable_node has been updated to be the new regular
1717          * stable_node. A collapse of the chain is indistinguishable
1718          * from the case there was no chain in the stable
1719          * rbtree. Otherwise stable_node is the chain and
1720          * stable_node_dup is the dup to replace.
1721          */
1722         if (stable_node_dup == stable_node) {
1723                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1724                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1725                 /* there is no chain */
1726                 if (page_node) {
1727                         VM_BUG_ON(page_node->head != &migrate_nodes);
1728                         list_del(&page_node->list);
1729                         DO_NUMA(page_node->nid = nid);
1730                         rb_replace_node(&stable_node_dup->node,
1731                                         &page_node->node,
1732                                         root);
1733                         if (is_page_sharing_candidate(page_node))
1734                                 get_page(page);
1735                         else
1736                                 page = NULL;
1737                 } else {
1738                         rb_erase(&stable_node_dup->node, root);
1739                         page = NULL;
1740                 }
1741         } else {
1742                 VM_BUG_ON(!is_stable_node_chain(stable_node));
1743                 __stable_node_dup_del(stable_node_dup);
1744                 if (page_node) {
1745                         VM_BUG_ON(page_node->head != &migrate_nodes);
1746                         list_del(&page_node->list);
1747                         DO_NUMA(page_node->nid = nid);
1748                         stable_node_chain_add_dup(page_node, stable_node);
1749                         if (is_page_sharing_candidate(page_node))
1750                                 get_page(page);
1751                         else
1752                                 page = NULL;
1753                 } else {
1754                         page = NULL;
1755                 }
1756         }
1757         stable_node_dup->head = &migrate_nodes;
1758         list_add(&stable_node_dup->list, stable_node_dup->head);
1759         return page;
1760
1761 chain_append:
1762         /* stable_node_dup could be null if it reached the limit */
1763         if (!stable_node_dup)
1764                 stable_node_dup = stable_node_any;
1765         /*
1766          * If stable_node was a chain and chain_prune collapsed it,
1767          * stable_node has been updated to be the new regular
1768          * stable_node. A collapse of the chain is indistinguishable
1769          * from the case there was no chain in the stable
1770          * rbtree. Otherwise stable_node is the chain and
1771          * stable_node_dup is the dup to replace.
1772          */
1773         if (stable_node_dup == stable_node) {
1774                 VM_BUG_ON(is_stable_node_chain(stable_node_dup));
1775                 VM_BUG_ON(is_stable_node_dup(stable_node_dup));
1776                 /* chain is missing so create it */
1777                 stable_node = alloc_stable_node_chain(stable_node_dup,
1778                                                       root);
1779                 if (!stable_node)
1780                         return NULL;
1781         }
1782         /*
1783          * Add this stable_node dup that was
1784          * migrated to the stable_node chain
1785          * of the current nid for this page
1786          * content.
1787          */
1788         VM_BUG_ON(!is_stable_node_chain(stable_node));
1789         VM_BUG_ON(!is_stable_node_dup(stable_node_dup));
1790         VM_BUG_ON(page_node->head != &migrate_nodes);
1791         list_del(&page_node->list);
1792         DO_NUMA(page_node->nid = nid);
1793         stable_node_chain_add_dup(page_node, stable_node);
1794         goto out;
1795 }
1796
1797 /*
1798  * stable_tree_insert - insert stable tree node pointing to new ksm page
1799  * into the stable tree.
1800  *
1801  * This function returns the stable tree node just allocated on success,
1802  * NULL otherwise.
1803  */
1804 static struct stable_node *stable_tree_insert(struct page *kpage)
1805 {
1806         int nid;
1807         unsigned long kpfn;
1808         struct rb_root *root;
1809         struct rb_node **new;
1810         struct rb_node *parent;
1811         struct stable_node *stable_node, *stable_node_dup, *stable_node_any;
1812         bool need_chain = false;
1813
1814         kpfn = page_to_pfn(kpage);
1815         nid = get_kpfn_nid(kpfn);
1816         root = root_stable_tree + nid;
1817 again:
1818         parent = NULL;
1819         new = &root->rb_node;
1820
1821         while (*new) {
1822                 struct page *tree_page;
1823                 int ret;
1824
1825                 cond_resched();
1826                 stable_node = rb_entry(*new, struct stable_node, node);
1827                 stable_node_any = NULL;
1828                 tree_page = chain(&stable_node_dup, stable_node, root);
1829                 if (!stable_node_dup) {
1830                         /*
1831                          * Either all stable_node dups were full in
1832                          * this stable_node chain, or this chain was
1833                          * empty and should be rb_erased.
1834                          */
1835                         stable_node_any = stable_node_dup_any(stable_node,
1836                                                               root);
1837                         if (!stable_node_any) {
1838                                 /* rb_erase just run */
1839                                 goto again;
1840                         }
1841                         /*
1842                          * Take any of the stable_node dups page of
1843                          * this stable_node chain to let the tree walk
1844                          * continue. All KSM pages belonging to the
1845                          * stable_node dups in a stable_node chain
1846                          * have the same content and they're
1847                          * write protected at all times. Any will work
1848                          * fine to continue the walk.
1849                          */
1850                         tree_page = get_ksm_page(stable_node_any,
1851                                                  GET_KSM_PAGE_NOLOCK);
1852                 }
1853                 VM_BUG_ON(!stable_node_dup ^ !!stable_node_any);
1854                 if (!tree_page) {
1855                         /*
1856                          * If we walked over a stale stable_node,
1857                          * get_ksm_page() will call rb_erase() and it
1858                          * may rebalance the tree from under us. So
1859                          * restart the search from scratch. Returning
1860                          * NULL would be safe too, but we'd generate
1861                          * false negative insertions just because some
1862                          * stable_node was stale.
1863                          */
1864                         goto again;
1865                 }
1866
1867                 ret = memcmp_pages(kpage, tree_page);
1868                 put_page(tree_page);
1869
1870                 parent = *new;
1871                 if (ret < 0)
1872                         new = &parent->rb_left;
1873                 else if (ret > 0)
1874                         new = &parent->rb_right;
1875                 else {
1876                         need_chain = true;
1877                         break;
1878                 }
1879         }
1880
1881         stable_node_dup = alloc_stable_node();
1882         if (!stable_node_dup)
1883                 return NULL;
1884
1885         INIT_HLIST_HEAD(&stable_node_dup->hlist);
1886         stable_node_dup->kpfn = kpfn;
1887         set_page_stable_node(kpage, stable_node_dup);
1888         stable_node_dup->rmap_hlist_len = 0;
1889         DO_NUMA(stable_node_dup->nid = nid);
1890         if (!need_chain) {
1891                 rb_link_node(&stable_node_dup->node, parent, new);
1892                 rb_insert_color(&stable_node_dup->node, root);
1893         } else {
1894                 if (!is_stable_node_chain(stable_node)) {
1895                         struct stable_node *orig = stable_node;
1896                         /* chain is missing so create it */
1897                         stable_node = alloc_stable_node_chain(orig, root);
1898                         if (!stable_node) {
1899                                 free_stable_node(stable_node_dup);
1900                                 return NULL;
1901                         }
1902                 }
1903                 stable_node_chain_add_dup(stable_node_dup, stable_node);
1904         }
1905
1906         return stable_node_dup;
1907 }
1908
1909 /*
1910  * unstable_tree_search_insert - search for identical page,
1911  * else insert rmap_item into the unstable tree.
1912  *
1913  * This function searches for a page in the unstable tree identical to the
1914  * page currently being scanned; and if no identical page is found in the
1915  * tree, we insert rmap_item as a new object into the unstable tree.
1916  *
1917  * This function returns pointer to rmap_item found to be identical
1918  * to the currently scanned page, NULL otherwise.
1919  *
1920  * This function does both searching and inserting, because they share
1921  * the same walking algorithm in an rbtree.
1922  */
1923 static
1924 struct rmap_item *unstable_tree_search_insert(struct rmap_item *rmap_item,
1925                                               struct page *page,
1926                                               struct page **tree_pagep)
1927 {
1928         struct rb_node **new;
1929         struct rb_root *root;
1930         struct rb_node *parent = NULL;
1931         int nid;
1932
1933         nid = get_kpfn_nid(page_to_pfn(page));
1934         root = root_unstable_tree + nid;
1935         new = &root->rb_node;
1936
1937         while (*new) {
1938                 struct rmap_item *tree_rmap_item;
1939                 struct page *tree_page;
1940                 int ret;
1941
1942                 cond_resched();
1943                 tree_rmap_item = rb_entry(*new, struct rmap_item, node);
1944                 tree_page = get_mergeable_page(tree_rmap_item);
1945                 if (!tree_page)
1946                         return NULL;
1947
1948                 /*
1949                  * Don't substitute a ksm page for a forked page.
1950                  */
1951                 if (page == tree_page) {
1952                         put_page(tree_page);
1953                         return NULL;
1954                 }
1955
1956                 ret = memcmp_pages(page, tree_page);
1957
1958                 parent = *new;
1959                 if (ret < 0) {
1960                         put_page(tree_page);
1961                         new = &parent->rb_left;
1962                 } else if (ret > 0) {
1963                         put_page(tree_page);
1964                         new = &parent->rb_right;
1965                 } else if (!ksm_merge_across_nodes &&
1966                            page_to_nid(tree_page) != nid) {
1967                         /*
1968                          * If tree_page has been migrated to another NUMA node,
1969                          * it will be flushed out and put in the right unstable
1970                          * tree next time: only merge with it when across_nodes.
1971                          */
1972                         put_page(tree_page);
1973                         return NULL;
1974                 } else {
1975                         *tree_pagep = tree_page;
1976                         return tree_rmap_item;
1977                 }
1978         }
1979
1980         rmap_item->address |= UNSTABLE_FLAG;
1981         rmap_item->address |= (ksm_scan.seqnr & SEQNR_MASK);
1982         DO_NUMA(rmap_item->nid = nid);
1983         rb_link_node(&rmap_item->node, parent, new);
1984         rb_insert_color(&rmap_item->node, root);
1985
1986         ksm_pages_unshared++;
1987         return NULL;
1988 }
1989
1990 /*
1991  * stable_tree_append - add another rmap_item to the linked list of
1992  * rmap_items hanging off a given node of the stable tree, all sharing
1993  * the same ksm page.
1994  */
1995 static void stable_tree_append(struct rmap_item *rmap_item,
1996                                struct stable_node *stable_node,
1997                                bool max_page_sharing_bypass)
1998 {
1999         /*
2000          * rmap won't find this mapping if we don't insert the
2001          * rmap_item in the right stable_node
2002          * duplicate. page_migration could break later if rmap breaks,
2003          * so we can as well crash here. We really need to check for
2004          * rmap_hlist_len == STABLE_NODE_CHAIN, but we can as well check
2005          * for other negative values as an underflow if detected here
2006          * for the first time (and not when decreasing rmap_hlist_len)
2007          * would be sign of memory corruption in the stable_node.
2008          */
2009         BUG_ON(stable_node->rmap_hlist_len < 0);
2010
2011         stable_node->rmap_hlist_len++;
2012         if (!max_page_sharing_bypass)
2013                 /* possibly non fatal but unexpected overflow, only warn */
2014                 WARN_ON_ONCE(stable_node->rmap_hlist_len >
2015                              ksm_max_page_sharing);
2016
2017         rmap_item->head = stable_node;
2018         rmap_item->address |= STABLE_FLAG;
2019         hlist_add_head(&rmap_item->hlist, &stable_node->hlist);
2020
2021         if (rmap_item->hlist.next)
2022                 ksm_pages_sharing++;
2023         else
2024                 ksm_pages_shared++;
2025 }
2026
2027 /*
2028  * cmp_and_merge_page - first see if page can be merged into the stable tree;
2029  * if not, compare checksum to previous and if it's the same, see if page can
2030  * be inserted into the unstable tree, or merged with a page already there and
2031  * both transferred to the stable tree.
2032  *
2033  * @page: the page that we are searching identical page to.
2034  * @rmap_item: the reverse mapping into the virtual address of this page
2035  */
2036 static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
2037 {
2038         struct mm_struct *mm = rmap_item->mm;
2039         struct rmap_item *tree_rmap_item;
2040         struct page *tree_page = NULL;
2041         struct stable_node *stable_node;
2042         struct page *kpage;
2043         unsigned int checksum;
2044         int err;
2045         bool max_page_sharing_bypass = false;
2046
2047         stable_node = page_stable_node(page);
2048         if (stable_node) {
2049                 if (stable_node->head != &migrate_nodes &&
2050                     get_kpfn_nid(READ_ONCE(stable_node->kpfn)) !=
2051                     NUMA(stable_node->nid)) {
2052                         stable_node_dup_del(stable_node);
2053                         stable_node->head = &migrate_nodes;
2054                         list_add(&stable_node->list, stable_node->head);
2055                 }
2056                 if (stable_node->head != &migrate_nodes &&
2057                     rmap_item->head == stable_node)
2058                         return;
2059                 /*
2060                  * If it's a KSM fork, allow it to go over the sharing limit
2061                  * without warnings.
2062                  */
2063                 if (!is_page_sharing_candidate(stable_node))
2064                         max_page_sharing_bypass = true;
2065         }
2066
2067         /* We first start with searching the page inside the stable tree */
2068         kpage = stable_tree_search(page);
2069         if (kpage == page && rmap_item->head == stable_node) {
2070                 put_page(kpage);
2071                 return;
2072         }
2073
2074         remove_rmap_item_from_tree(rmap_item);
2075
2076         if (kpage) {
2077                 if (PTR_ERR(kpage) == -EBUSY)
2078                         return;
2079
2080                 err = try_to_merge_with_ksm_page(rmap_item, page, kpage);
2081                 if (!err) {
2082                         /*
2083                          * The page was successfully merged:
2084                          * add its rmap_item to the stable tree.
2085                          */
2086                         lock_page(kpage);
2087                         stable_tree_append(rmap_item, page_stable_node(kpage),
2088                                            max_page_sharing_bypass);
2089                         unlock_page(kpage);
2090                 }
2091                 put_page(kpage);
2092                 return;
2093         }
2094
2095         /*
2096          * If the hash value of the page has changed from the last time
2097          * we calculated it, this page is changing frequently: therefore we
2098          * don't want to insert it in the unstable tree, and we don't want
2099          * to waste our time searching for something identical to it there.
2100          */
2101         checksum = calc_checksum(page);
2102         if (rmap_item->oldchecksum != checksum) {
2103                 rmap_item->oldchecksum = checksum;
2104                 return;
2105         }
2106
2107         /*
2108          * Same checksum as an empty page. We attempt to merge it with the
2109          * appropriate zero page if the user enabled this via sysfs.
2110          */
2111         if (ksm_use_zero_pages && (checksum == zero_checksum)) {
2112                 struct vm_area_struct *vma;
2113
2114                 mmap_read_lock(mm);
2115                 vma = find_mergeable_vma(mm, rmap_item->address);
2116                 if (vma) {
2117                         err = try_to_merge_one_page(vma, page,
2118                                         ZERO_PAGE(rmap_item->address));
2119                 } else {
2120                         /*
2121                          * If the vma is out of date, we do not need to
2122                          * continue.
2123                          */
2124                         err = 0;
2125                 }
2126                 mmap_read_unlock(mm);
2127                 /*
2128                  * In case of failure, the page was not really empty, so we
2129                  * need to continue. Otherwise we're done.
2130                  */
2131                 if (!err)
2132                         return;
2133         }
2134         tree_rmap_item =
2135                 unstable_tree_search_insert(rmap_item, page, &tree_page);
2136         if (tree_rmap_item) {
2137                 bool split;
2138
2139                 kpage = try_to_merge_two_pages(rmap_item, page,
2140                                                 tree_rmap_item, tree_page);
2141                 /*
2142                  * If both pages we tried to merge belong to the same compound
2143                  * page, then we actually ended up increasing the reference
2144                  * count of the same compound page twice, and split_huge_page
2145                  * failed.
2146                  * Here we set a flag if that happened, and we use it later to
2147                  * try split_huge_page again. Since we call put_page right
2148                  * afterwards, the reference count will be correct and
2149                  * split_huge_page should succeed.
2150                  */
2151                 split = PageTransCompound(page)
2152                         && compound_head(page) == compound_head(tree_page);
2153                 put_page(tree_page);
2154                 if (kpage) {
2155                         /*
2156                          * The pages were successfully merged: insert new
2157                          * node in the stable tree and add both rmap_items.
2158                          */
2159                         lock_page(kpage);
2160                         stable_node = stable_tree_insert(kpage);
2161                         if (stable_node) {
2162                                 stable_tree_append(tree_rmap_item, stable_node,
2163                                                    false);
2164                                 stable_tree_append(rmap_item, stable_node,
2165                                                    false);
2166                         }
2167                         unlock_page(kpage);
2168
2169                         /*
2170                          * If we fail to insert the page into the stable tree,
2171                          * we will have 2 virtual addresses that are pointing
2172                          * to a ksm page left outside the stable tree,
2173                          * in which case we need to break_cow on both.
2174                          */
2175                         if (!stable_node) {
2176                                 break_cow(tree_rmap_item);
2177                                 break_cow(rmap_item);
2178                         }
2179                 } else if (split) {
2180                         /*
2181                          * We are here if we tried to merge two pages and
2182                          * failed because they both belonged to the same
2183                          * compound page. We will split the page now, but no
2184                          * merging will take place.
2185                          * We do not want to add the cost of a full lock; if
2186                          * the page is locked, it is better to skip it and
2187                          * perhaps try again later.
2188                          */
2189                         if (!trylock_page(page))
2190                                 return;
2191                         split_huge_page(page);
2192                         unlock_page(page);
2193                 }
2194         }
2195 }
2196
2197 static struct rmap_item *get_next_rmap_item(struct mm_slot *mm_slot,
2198                                             struct rmap_item **rmap_list,
2199                                             unsigned long addr)
2200 {
2201         struct rmap_item *rmap_item;
2202
2203         while (*rmap_list) {
2204                 rmap_item = *rmap_list;
2205                 if ((rmap_item->address & PAGE_MASK) == addr)
2206                         return rmap_item;
2207                 if (rmap_item->address > addr)
2208                         break;
2209                 *rmap_list = rmap_item->rmap_list;
2210                 remove_rmap_item_from_tree(rmap_item);
2211                 free_rmap_item(rmap_item);
2212         }
2213
2214         rmap_item = alloc_rmap_item();
2215         if (rmap_item) {
2216                 /* It has already been zeroed */
2217                 rmap_item->mm = mm_slot->mm;
2218                 rmap_item->address = addr;
2219                 rmap_item->rmap_list = *rmap_list;
2220                 *rmap_list = rmap_item;
2221         }
2222         return rmap_item;
2223 }
2224
2225 static struct rmap_item *scan_get_next_rmap_item(struct page **page)
2226 {
2227         struct mm_struct *mm;
2228         struct mm_slot *slot;
2229         struct vm_area_struct *vma;
2230         struct rmap_item *rmap_item;
2231         int nid;
2232
2233         if (list_empty(&ksm_mm_head.mm_list))
2234                 return NULL;
2235
2236         slot = ksm_scan.mm_slot;
2237         if (slot == &ksm_mm_head) {
2238                 /*
2239                  * A number of pages can hang around indefinitely on per-cpu
2240                  * pagevecs, raised page count preventing write_protect_page
2241                  * from merging them.  Though it doesn't really matter much,
2242                  * it is puzzling to see some stuck in pages_volatile until
2243                  * other activity jostles them out, and they also prevented
2244                  * LTP's KSM test from succeeding deterministically; so drain
2245                  * them here (here rather than on entry to ksm_do_scan(),
2246                  * so we don't IPI too often when pages_to_scan is set low).
2247                  */
2248                 lru_add_drain_all();
2249
2250                 /*
2251                  * Whereas stale stable_nodes on the stable_tree itself
2252                  * get pruned in the regular course of stable_tree_search(),
2253                  * those moved out to the migrate_nodes list can accumulate:
2254                  * so prune them once before each full scan.
2255                  */
2256                 if (!ksm_merge_across_nodes) {
2257                         struct stable_node *stable_node, *next;
2258                         struct page *page;
2259
2260                         list_for_each_entry_safe(stable_node, next,
2261                                                  &migrate_nodes, list) {
2262                                 page = get_ksm_page(stable_node,
2263                                                     GET_KSM_PAGE_NOLOCK);
2264                                 if (page)
2265                                         put_page(page);
2266                                 cond_resched();
2267                         }
2268                 }
2269
2270                 for (nid = 0; nid < ksm_nr_node_ids; nid++)
2271                         root_unstable_tree[nid] = RB_ROOT;
2272
2273                 spin_lock(&ksm_mmlist_lock);
2274                 slot = list_entry(slot->mm_list.next, struct mm_slot, mm_list);
2275                 ksm_scan.mm_slot = slot;
2276                 spin_unlock(&ksm_mmlist_lock);
2277                 /*
2278                  * Although we tested list_empty() above, a racing __ksm_exit
2279                  * of the last mm on the list may have removed it since then.
2280                  */
2281                 if (slot == &ksm_mm_head)
2282                         return NULL;
2283 next_mm:
2284                 ksm_scan.address = 0;
2285                 ksm_scan.rmap_list = &slot->rmap_list;
2286         }
2287
2288         mm = slot->mm;
2289         mmap_read_lock(mm);
2290         if (ksm_test_exit(mm))
2291                 vma = NULL;
2292         else
2293                 vma = find_vma(mm, ksm_scan.address);
2294
2295         for (; vma; vma = vma->vm_next) {
2296                 if (!(vma->vm_flags & VM_MERGEABLE))
2297                         continue;
2298                 if (ksm_scan.address < vma->vm_start)
2299                         ksm_scan.address = vma->vm_start;
2300                 if (!vma->anon_vma)
2301                         ksm_scan.address = vma->vm_end;
2302
2303                 while (ksm_scan.address < vma->vm_end) {
2304                         if (ksm_test_exit(mm))
2305                                 break;
2306                         *page = follow_page(vma, ksm_scan.address, FOLL_GET);
2307                         if (IS_ERR_OR_NULL(*page)) {
2308                                 ksm_scan.address += PAGE_SIZE;
2309                                 cond_resched();
2310                                 continue;
2311                         }
2312                         if (PageAnon(*page)) {
2313                                 flush_anon_page(vma, *page, ksm_scan.address);
2314                                 flush_dcache_page(*page);
2315                                 rmap_item = get_next_rmap_item(slot,
2316                                         ksm_scan.rmap_list, ksm_scan.address);
2317                                 if (rmap_item) {
2318                                         ksm_scan.rmap_list =
2319                                                         &rmap_item->rmap_list;
2320                                         ksm_scan.address += PAGE_SIZE;
2321                                 } else
2322                                         put_page(*page);
2323                                 mmap_read_unlock(mm);
2324                                 return rmap_item;
2325                         }
2326                         put_page(*page);
2327                         ksm_scan.address += PAGE_SIZE;
2328                         cond_resched();
2329                 }
2330         }
2331
2332         if (ksm_test_exit(mm)) {
2333                 ksm_scan.address = 0;
2334                 ksm_scan.rmap_list = &slot->rmap_list;
2335         }
2336         /*
2337          * Nuke all the rmap_items that are above this current rmap:
2338          * because there were no VM_MERGEABLE vmas with such addresses.
2339          */
2340         remove_trailing_rmap_items(slot, ksm_scan.rmap_list);
2341
2342         spin_lock(&ksm_mmlist_lock);
2343         ksm_scan.mm_slot = list_entry(slot->mm_list.next,
2344                                                 struct mm_slot, mm_list);
2345         if (ksm_scan.address == 0) {
2346                 /*
2347                  * We've completed a full scan of all vmas, holding mmap_lock
2348                  * throughout, and found no VM_MERGEABLE: so do the same as
2349                  * __ksm_exit does to remove this mm from all our lists now.
2350                  * This applies either when cleaning up after __ksm_exit
2351                  * (but beware: we can reach here even before __ksm_exit),
2352                  * or when all VM_MERGEABLE areas have been unmapped (and
2353                  * mmap_lock then protects against race with MADV_MERGEABLE).
2354                  */
2355                 hash_del(&slot->link);
2356                 list_del(&slot->mm_list);
2357                 spin_unlock(&ksm_mmlist_lock);
2358
2359                 free_mm_slot(slot);
2360                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2361                 mmap_read_unlock(mm);
2362                 mmdrop(mm);
2363         } else {
2364                 mmap_read_unlock(mm);
2365                 /*
2366                  * mmap_read_unlock(mm) first because after
2367                  * spin_unlock(&ksm_mmlist_lock) run, the "mm" may
2368                  * already have been freed under us by __ksm_exit()
2369                  * because the "mm_slot" is still hashed and
2370                  * ksm_scan.mm_slot doesn't point to it anymore.
2371                  */
2372                 spin_unlock(&ksm_mmlist_lock);
2373         }
2374
2375         /* Repeat until we've completed scanning the whole list */
2376         slot = ksm_scan.mm_slot;
2377         if (slot != &ksm_mm_head)
2378                 goto next_mm;
2379
2380         ksm_scan.seqnr++;
2381         return NULL;
2382 }
2383
2384 /**
2385  * ksm_do_scan  - the ksm scanner main worker function.
2386  * @scan_npages:  number of pages we want to scan before we return.
2387  */
2388 static void ksm_do_scan(unsigned int scan_npages)
2389 {
2390         struct rmap_item *rmap_item;
2391         struct page *page;
2392
2393         while (scan_npages-- && likely(!freezing(current))) {
2394                 cond_resched();
2395                 rmap_item = scan_get_next_rmap_item(&page);
2396                 if (!rmap_item)
2397                         return;
2398                 cmp_and_merge_page(page, rmap_item);
2399                 put_page(page);
2400         }
2401 }
2402
2403 static int ksmd_should_run(void)
2404 {
2405         return (ksm_run & KSM_RUN_MERGE) && !list_empty(&ksm_mm_head.mm_list);
2406 }
2407
2408 static int ksm_scan_thread(void *nothing)
2409 {
2410         unsigned int sleep_ms;
2411
2412         set_freezable();
2413         set_user_nice(current, 5);
2414
2415         while (!kthread_should_stop()) {
2416                 mutex_lock(&ksm_thread_mutex);
2417                 wait_while_offlining();
2418                 if (ksmd_should_run())
2419                         ksm_do_scan(ksm_thread_pages_to_scan);
2420                 mutex_unlock(&ksm_thread_mutex);
2421
2422                 try_to_freeze();
2423
2424                 if (ksmd_should_run()) {
2425                         sleep_ms = READ_ONCE(ksm_thread_sleep_millisecs);
2426                         wait_event_interruptible_timeout(ksm_iter_wait,
2427                                 sleep_ms != READ_ONCE(ksm_thread_sleep_millisecs),
2428                                 msecs_to_jiffies(sleep_ms));
2429                 } else {
2430                         wait_event_freezable(ksm_thread_wait,
2431                                 ksmd_should_run() || kthread_should_stop());
2432                 }
2433         }
2434         return 0;
2435 }
2436
2437 int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
2438                 unsigned long end, int advice, unsigned long *vm_flags)
2439 {
2440         struct mm_struct *mm = vma->vm_mm;
2441         int err;
2442
2443         switch (advice) {
2444         case MADV_MERGEABLE:
2445                 /*
2446                  * Be somewhat over-protective for now!
2447                  */
2448                 if (*vm_flags & (VM_MERGEABLE | VM_SHARED  | VM_MAYSHARE   |
2449                                  VM_PFNMAP    | VM_IO      | VM_DONTEXPAND |
2450                                  VM_HUGETLB | VM_MIXEDMAP))
2451                         return 0;               /* just ignore the advice */
2452
2453                 if (vma_is_dax(vma))
2454                         return 0;
2455
2456 #ifdef VM_SAO
2457                 if (*vm_flags & VM_SAO)
2458                         return 0;
2459 #endif
2460 #ifdef VM_SPARC_ADI
2461                 if (*vm_flags & VM_SPARC_ADI)
2462                         return 0;
2463 #endif
2464
2465                 if (!test_bit(MMF_VM_MERGEABLE, &mm->flags)) {
2466                         err = __ksm_enter(mm);
2467                         if (err)
2468                                 return err;
2469                 }
2470
2471                 *vm_flags |= VM_MERGEABLE;
2472                 break;
2473
2474         case MADV_UNMERGEABLE:
2475                 if (!(*vm_flags & VM_MERGEABLE))
2476                         return 0;               /* just ignore the advice */
2477
2478                 if (vma->anon_vma) {
2479                         err = unmerge_ksm_pages(vma, start, end);
2480                         if (err)
2481                                 return err;
2482                 }
2483
2484                 *vm_flags &= ~VM_MERGEABLE;
2485                 break;
2486         }
2487
2488         return 0;
2489 }
2490 EXPORT_SYMBOL_GPL(ksm_madvise);
2491
2492 int __ksm_enter(struct mm_struct *mm)
2493 {
2494         struct mm_slot *mm_slot;
2495         int needs_wakeup;
2496
2497         mm_slot = alloc_mm_slot();
2498         if (!mm_slot)
2499                 return -ENOMEM;
2500
2501         /* Check ksm_run too?  Would need tighter locking */
2502         needs_wakeup = list_empty(&ksm_mm_head.mm_list);
2503
2504         spin_lock(&ksm_mmlist_lock);
2505         insert_to_mm_slots_hash(mm, mm_slot);
2506         /*
2507          * When KSM_RUN_MERGE (or KSM_RUN_STOP),
2508          * insert just behind the scanning cursor, to let the area settle
2509          * down a little; when fork is followed by immediate exec, we don't
2510          * want ksmd to waste time setting up and tearing down an rmap_list.
2511          *
2512          * But when KSM_RUN_UNMERGE, it's important to insert ahead of its
2513          * scanning cursor, otherwise KSM pages in newly forked mms will be
2514          * missed: then we might as well insert at the end of the list.
2515          */
2516         if (ksm_run & KSM_RUN_UNMERGE)
2517                 list_add_tail(&mm_slot->mm_list, &ksm_mm_head.mm_list);
2518         else
2519                 list_add_tail(&mm_slot->mm_list, &ksm_scan.mm_slot->mm_list);
2520         spin_unlock(&ksm_mmlist_lock);
2521
2522         set_bit(MMF_VM_MERGEABLE, &mm->flags);
2523         mmgrab(mm);
2524
2525         if (needs_wakeup)
2526                 wake_up_interruptible(&ksm_thread_wait);
2527
2528         return 0;
2529 }
2530
2531 void __ksm_exit(struct mm_struct *mm)
2532 {
2533         struct mm_slot *mm_slot;
2534         int easy_to_free = 0;
2535
2536         /*
2537          * This process is exiting: if it's straightforward (as is the
2538          * case when ksmd was never running), free mm_slot immediately.
2539          * But if it's at the cursor or has rmap_items linked to it, use
2540          * mmap_lock to synchronize with any break_cows before pagetables
2541          * are freed, and leave the mm_slot on the list for ksmd to free.
2542          * Beware: ksm may already have noticed it exiting and freed the slot.
2543          */
2544
2545         spin_lock(&ksm_mmlist_lock);
2546         mm_slot = get_mm_slot(mm);
2547         if (mm_slot && ksm_scan.mm_slot != mm_slot) {
2548                 if (!mm_slot->rmap_list) {
2549                         hash_del(&mm_slot->link);
2550                         list_del(&mm_slot->mm_list);
2551                         easy_to_free = 1;
2552                 } else {
2553                         list_move(&mm_slot->mm_list,
2554                                   &ksm_scan.mm_slot->mm_list);
2555                 }
2556         }
2557         spin_unlock(&ksm_mmlist_lock);
2558
2559         if (easy_to_free) {
2560                 free_mm_slot(mm_slot);
2561                 clear_bit(MMF_VM_MERGEABLE, &mm->flags);
2562                 mmdrop(mm);
2563         } else if (mm_slot) {
2564                 mmap_write_lock(mm);
2565                 mmap_write_unlock(mm);
2566         }
2567 }
2568
2569 struct page *ksm_might_need_to_copy(struct page *page,
2570                         struct vm_area_struct *vma, unsigned long address)
2571 {
2572         struct anon_vma *anon_vma = page_anon_vma(page);
2573         struct page *new_page;
2574
2575         if (PageKsm(page)) {
2576                 if (page_stable_node(page) &&
2577                     !(ksm_run & KSM_RUN_UNMERGE))
2578                         return page;    /* no need to copy it */
2579         } else if (!anon_vma) {
2580                 return page;            /* no need to copy it */
2581         } else if (anon_vma->root == vma->anon_vma->root &&
2582                  page->index == linear_page_index(vma, address)) {
2583                 return page;            /* still no need to copy it */
2584         }
2585         if (!PageUptodate(page))
2586                 return page;            /* let do_swap_page report the error */
2587
2588         new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, address);
2589         if (new_page && mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL)) {
2590                 put_page(new_page);
2591                 new_page = NULL;
2592         }
2593         if (new_page) {
2594                 copy_user_highpage(new_page, page, address, vma);
2595
2596                 SetPageDirty(new_page);
2597                 __SetPageUptodate(new_page);
2598                 __SetPageLocked(new_page);
2599         }
2600
2601         return new_page;
2602 }
2603
2604 void rmap_walk_ksm(struct page *page, struct rmap_walk_control *rwc)
2605 {
2606         struct stable_node *stable_node;
2607         struct rmap_item *rmap_item;
2608         int search_new_forks = 0;
2609
2610         VM_BUG_ON_PAGE(!PageKsm(page), page);
2611
2612         /*
2613          * Rely on the page lock to protect against concurrent modifications
2614          * to that page's node of the stable tree.
2615          */
2616         VM_BUG_ON_PAGE(!PageLocked(page), page);
2617
2618         stable_node = page_stable_node(page);
2619         if (!stable_node)
2620                 return;
2621 again:
2622         hlist_for_each_entry(rmap_item, &stable_node->hlist, hlist) {
2623                 struct anon_vma *anon_vma = rmap_item->anon_vma;
2624                 struct anon_vma_chain *vmac;
2625                 struct vm_area_struct *vma;
2626
2627                 cond_resched();
2628                 anon_vma_lock_read(anon_vma);
2629                 anon_vma_interval_tree_foreach(vmac, &anon_vma->rb_root,
2630                                                0, ULONG_MAX) {
2631                         unsigned long addr;
2632
2633                         cond_resched();
2634                         vma = vmac->vma;
2635
2636                         /* Ignore the stable/unstable/sqnr flags */
2637                         addr = rmap_item->address & ~KSM_FLAG_MASK;
2638
2639                         if (addr < vma->vm_start || addr >= vma->vm_end)
2640                                 continue;
2641                         /*
2642                          * Initially we examine only the vma which covers this
2643                          * rmap_item; but later, if there is still work to do,
2644                          * we examine covering vmas in other mms: in case they
2645                          * were forked from the original since ksmd passed.
2646                          */
2647                         if ((rmap_item->mm == vma->vm_mm) == search_new_forks)
2648                                 continue;
2649
2650                         if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
2651                                 continue;
2652
2653                         if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
2654                                 anon_vma_unlock_read(anon_vma);
2655                                 return;
2656                         }
2657                         if (rwc->done && rwc->done(page)) {
2658                                 anon_vma_unlock_read(anon_vma);
2659                                 return;
2660                         }
2661                 }
2662                 anon_vma_unlock_read(anon_vma);
2663         }
2664         if (!search_new_forks++)
2665                 goto again;
2666 }
2667
2668 #ifdef CONFIG_MIGRATION
2669 void ksm_migrate_page(struct page *newpage, struct page *oldpage)
2670 {
2671         struct stable_node *stable_node;
2672
2673         VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
2674         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
2675         VM_BUG_ON_PAGE(newpage->mapping != oldpage->mapping, newpage);
2676
2677         stable_node = page_stable_node(newpage);
2678         if (stable_node) {
2679                 VM_BUG_ON_PAGE(stable_node->kpfn != page_to_pfn(oldpage), oldpage);
2680                 stable_node->kpfn = page_to_pfn(newpage);
2681                 /*
2682                  * newpage->mapping was set in advance; now we need smp_wmb()
2683                  * to make sure that the new stable_node->kpfn is visible
2684                  * to get_ksm_page() before it can see that oldpage->mapping
2685                  * has gone stale (or that PageSwapCache has been cleared).
2686                  */
2687                 smp_wmb();
2688                 set_page_stable_node(oldpage, NULL);
2689         }
2690 }
2691 #endif /* CONFIG_MIGRATION */
2692
2693 #ifdef CONFIG_MEMORY_HOTREMOVE
2694 static void wait_while_offlining(void)
2695 {
2696         while (ksm_run & KSM_RUN_OFFLINE) {
2697                 mutex_unlock(&ksm_thread_mutex);
2698                 wait_on_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE),
2699                             TASK_UNINTERRUPTIBLE);
2700                 mutex_lock(&ksm_thread_mutex);
2701         }
2702 }
2703
2704 static bool stable_node_dup_remove_range(struct stable_node *stable_node,
2705                                          unsigned long start_pfn,
2706                                          unsigned long end_pfn)
2707 {
2708         if (stable_node->kpfn >= start_pfn &&
2709             stable_node->kpfn < end_pfn) {
2710                 /*
2711                  * Don't get_ksm_page, page has already gone:
2712                  * which is why we keep kpfn instead of page*
2713                  */
2714                 remove_node_from_stable_tree(stable_node);
2715                 return true;
2716         }
2717         return false;
2718 }
2719
2720 static bool stable_node_chain_remove_range(struct stable_node *stable_node,
2721                                            unsigned long start_pfn,
2722                                            unsigned long end_pfn,
2723                                            struct rb_root *root)
2724 {
2725         struct stable_node *dup;
2726         struct hlist_node *hlist_safe;
2727
2728         if (!is_stable_node_chain(stable_node)) {
2729                 VM_BUG_ON(is_stable_node_dup(stable_node));
2730                 return stable_node_dup_remove_range(stable_node, start_pfn,
2731                                                     end_pfn);
2732         }
2733
2734         hlist_for_each_entry_safe(dup, hlist_safe,
2735                                   &stable_node->hlist, hlist_dup) {
2736                 VM_BUG_ON(!is_stable_node_dup(dup));
2737                 stable_node_dup_remove_range(dup, start_pfn, end_pfn);
2738         }
2739         if (hlist_empty(&stable_node->hlist)) {
2740                 free_stable_node_chain(stable_node, root);
2741                 return true; /* notify caller that tree was rebalanced */
2742         } else
2743                 return false;
2744 }
2745
2746 static void ksm_check_stable_tree(unsigned long start_pfn,
2747                                   unsigned long end_pfn)
2748 {
2749         struct stable_node *stable_node, *next;
2750         struct rb_node *node;
2751         int nid;
2752
2753         for (nid = 0; nid < ksm_nr_node_ids; nid++) {
2754                 node = rb_first(root_stable_tree + nid);
2755                 while (node) {
2756                         stable_node = rb_entry(node, struct stable_node, node);
2757                         if (stable_node_chain_remove_range(stable_node,
2758                                                            start_pfn, end_pfn,
2759                                                            root_stable_tree +
2760                                                            nid))
2761                                 node = rb_first(root_stable_tree + nid);
2762                         else
2763                                 node = rb_next(node);
2764                         cond_resched();
2765                 }
2766         }
2767         list_for_each_entry_safe(stable_node, next, &migrate_nodes, list) {
2768                 if (stable_node->kpfn >= start_pfn &&
2769                     stable_node->kpfn < end_pfn)
2770                         remove_node_from_stable_tree(stable_node);
2771                 cond_resched();
2772         }
2773 }
2774
2775 static int ksm_memory_callback(struct notifier_block *self,
2776                                unsigned long action, void *arg)
2777 {
2778         struct memory_notify *mn = arg;
2779
2780         switch (action) {
2781         case MEM_GOING_OFFLINE:
2782                 /*
2783                  * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
2784                  * and remove_all_stable_nodes() while memory is going offline:
2785                  * it is unsafe for them to touch the stable tree at this time.
2786                  * But unmerge_ksm_pages(), rmap lookups and other entry points
2787                  * which do not need the ksm_thread_mutex are all safe.
2788                  */
2789                 mutex_lock(&ksm_thread_mutex);
2790                 ksm_run |= KSM_RUN_OFFLINE;
2791                 mutex_unlock(&ksm_thread_mutex);
2792                 break;
2793
2794         case MEM_OFFLINE:
2795                 /*
2796                  * Most of the work is done by page migration; but there might
2797                  * be a few stable_nodes left over, still pointing to struct
2798                  * pages which have been offlined: prune those from the tree,
2799                  * otherwise get_ksm_page() might later try to access a
2800                  * non-existent struct page.
2801                  */
2802                 ksm_check_stable_tree(mn->start_pfn,
2803                                       mn->start_pfn + mn->nr_pages);
2804                 fallthrough;
2805         case MEM_CANCEL_OFFLINE:
2806                 mutex_lock(&ksm_thread_mutex);
2807                 ksm_run &= ~KSM_RUN_OFFLINE;
2808                 mutex_unlock(&ksm_thread_mutex);
2809
2810                 smp_mb();       /* wake_up_bit advises this */
2811                 wake_up_bit(&ksm_run, ilog2(KSM_RUN_OFFLINE));
2812                 break;
2813         }
2814         return NOTIFY_OK;
2815 }
2816 #else
2817 static void wait_while_offlining(void)
2818 {
2819 }
2820 #endif /* CONFIG_MEMORY_HOTREMOVE */
2821
2822 #ifdef CONFIG_SYSFS
2823 /*
2824  * This all compiles without CONFIG_SYSFS, but is a waste of space.
2825  */
2826
2827 #define KSM_ATTR_RO(_name) \
2828         static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
2829 #define KSM_ATTR(_name) \
2830         static struct kobj_attribute _name##_attr = \
2831                 __ATTR(_name, 0644, _name##_show, _name##_store)
2832
2833 static ssize_t sleep_millisecs_show(struct kobject *kobj,
2834                                     struct kobj_attribute *attr, char *buf)
2835 {
2836         return sysfs_emit(buf, "%u\n", ksm_thread_sleep_millisecs);
2837 }
2838
2839 static ssize_t sleep_millisecs_store(struct kobject *kobj,
2840                                      struct kobj_attribute *attr,
2841                                      const char *buf, size_t count)
2842 {
2843         unsigned int msecs;
2844         int err;
2845
2846         err = kstrtouint(buf, 10, &msecs);
2847         if (err)
2848                 return -EINVAL;
2849
2850         ksm_thread_sleep_millisecs = msecs;
2851         wake_up_interruptible(&ksm_iter_wait);
2852
2853         return count;
2854 }
2855 KSM_ATTR(sleep_millisecs);
2856
2857 static ssize_t pages_to_scan_show(struct kobject *kobj,
2858                                   struct kobj_attribute *attr, char *buf)
2859 {
2860         return sysfs_emit(buf, "%u\n", ksm_thread_pages_to_scan);
2861 }
2862
2863 static ssize_t pages_to_scan_store(struct kobject *kobj,
2864                                    struct kobj_attribute *attr,
2865                                    const char *buf, size_t count)
2866 {
2867         unsigned int nr_pages;
2868         int err;
2869
2870         err = kstrtouint(buf, 10, &nr_pages);
2871         if (err)
2872                 return -EINVAL;
2873
2874         ksm_thread_pages_to_scan = nr_pages;
2875
2876         return count;
2877 }
2878 KSM_ATTR(pages_to_scan);
2879
2880 static ssize_t run_show(struct kobject *kobj, struct kobj_attribute *attr,
2881                         char *buf)
2882 {
2883         return sysfs_emit(buf, "%lu\n", ksm_run);
2884 }
2885
2886 static ssize_t run_store(struct kobject *kobj, struct kobj_attribute *attr,
2887                          const char *buf, size_t count)
2888 {
2889         unsigned int flags;
2890         int err;
2891
2892         err = kstrtouint(buf, 10, &flags);
2893         if (err)
2894                 return -EINVAL;
2895         if (flags > KSM_RUN_UNMERGE)
2896                 return -EINVAL;
2897
2898         /*
2899          * KSM_RUN_MERGE sets ksmd running, and 0 stops it running.
2900          * KSM_RUN_UNMERGE stops it running and unmerges all rmap_items,
2901          * breaking COW to free the pages_shared (but leaves mm_slots
2902          * on the list for when ksmd may be set running again).
2903          */
2904
2905         mutex_lock(&ksm_thread_mutex);
2906         wait_while_offlining();
2907         if (ksm_run != flags) {
2908                 ksm_run = flags;
2909                 if (flags & KSM_RUN_UNMERGE) {
2910                         set_current_oom_origin();
2911                         err = unmerge_and_remove_all_rmap_items();
2912                         clear_current_oom_origin();
2913                         if (err) {
2914                                 ksm_run = KSM_RUN_STOP;
2915                                 count = err;
2916                         }
2917                 }
2918         }
2919         mutex_unlock(&ksm_thread_mutex);
2920
2921         if (flags & KSM_RUN_MERGE)
2922                 wake_up_interruptible(&ksm_thread_wait);
2923
2924         return count;
2925 }
2926 KSM_ATTR(run);
2927
2928 #ifdef CONFIG_NUMA
2929 static ssize_t merge_across_nodes_show(struct kobject *kobj,
2930                                        struct kobj_attribute *attr, char *buf)
2931 {
2932         return sysfs_emit(buf, "%u\n", ksm_merge_across_nodes);
2933 }
2934
2935 static ssize_t merge_across_nodes_store(struct kobject *kobj,
2936                                    struct kobj_attribute *attr,
2937                                    const char *buf, size_t count)
2938 {
2939         int err;
2940         unsigned long knob;
2941
2942         err = kstrtoul(buf, 10, &knob);
2943         if (err)
2944                 return err;
2945         if (knob > 1)
2946                 return -EINVAL;
2947
2948         mutex_lock(&ksm_thread_mutex);
2949         wait_while_offlining();
2950         if (ksm_merge_across_nodes != knob) {
2951                 if (ksm_pages_shared || remove_all_stable_nodes())
2952                         err = -EBUSY;
2953                 else if (root_stable_tree == one_stable_tree) {
2954                         struct rb_root *buf;
2955                         /*
2956                          * This is the first time that we switch away from the
2957                          * default of merging across nodes: must now allocate
2958                          * a buffer to hold as many roots as may be needed.
2959                          * Allocate stable and unstable together:
2960                          * MAXSMP NODES_SHIFT 10 will use 16kB.
2961                          */
2962                         buf = kcalloc(nr_node_ids + nr_node_ids, sizeof(*buf),
2963                                       GFP_KERNEL);
2964                         /* Let us assume that RB_ROOT is NULL is zero */
2965                         if (!buf)
2966                                 err = -ENOMEM;
2967                         else {
2968                                 root_stable_tree = buf;
2969                                 root_unstable_tree = buf + nr_node_ids;
2970                                 /* Stable tree is empty but not the unstable */
2971                                 root_unstable_tree[0] = one_unstable_tree[0];
2972                         }
2973                 }
2974                 if (!err) {
2975                         ksm_merge_across_nodes = knob;
2976                         ksm_nr_node_ids = knob ? 1 : nr_node_ids;
2977                 }
2978         }
2979         mutex_unlock(&ksm_thread_mutex);
2980
2981         return err ? err : count;
2982 }
2983 KSM_ATTR(merge_across_nodes);
2984 #endif
2985
2986 static ssize_t use_zero_pages_show(struct kobject *kobj,
2987                                    struct kobj_attribute *attr, char *buf)
2988 {
2989         return sysfs_emit(buf, "%u\n", ksm_use_zero_pages);
2990 }
2991 static ssize_t use_zero_pages_store(struct kobject *kobj,
2992                                    struct kobj_attribute *attr,
2993                                    const char *buf, size_t count)
2994 {
2995         int err;
2996         bool value;
2997
2998         err = kstrtobool(buf, &value);
2999         if (err)
3000                 return -EINVAL;
3001
3002         ksm_use_zero_pages = value;
3003
3004         return count;
3005 }
3006 KSM_ATTR(use_zero_pages);
3007
3008 static ssize_t max_page_sharing_show(struct kobject *kobj,
3009                                      struct kobj_attribute *attr, char *buf)
3010 {
3011         return sysfs_emit(buf, "%u\n", ksm_max_page_sharing);
3012 }
3013
3014 static ssize_t max_page_sharing_store(struct kobject *kobj,
3015                                       struct kobj_attribute *attr,
3016                                       const char *buf, size_t count)
3017 {
3018         int err;
3019         int knob;
3020
3021         err = kstrtoint(buf, 10, &knob);
3022         if (err)
3023                 return err;
3024         /*
3025          * When a KSM page is created it is shared by 2 mappings. This
3026          * being a signed comparison, it implicitly verifies it's not
3027          * negative.
3028          */
3029         if (knob < 2)
3030                 return -EINVAL;
3031
3032         if (READ_ONCE(ksm_max_page_sharing) == knob)
3033                 return count;
3034
3035         mutex_lock(&ksm_thread_mutex);
3036         wait_while_offlining();
3037         if (ksm_max_page_sharing != knob) {
3038                 if (ksm_pages_shared || remove_all_stable_nodes())
3039                         err = -EBUSY;
3040                 else
3041                         ksm_max_page_sharing = knob;
3042         }
3043         mutex_unlock(&ksm_thread_mutex);
3044
3045         return err ? err : count;
3046 }
3047 KSM_ATTR(max_page_sharing);
3048
3049 static ssize_t pages_shared_show(struct kobject *kobj,
3050                                  struct kobj_attribute *attr, char *buf)
3051 {
3052         return sysfs_emit(buf, "%lu\n", ksm_pages_shared);
3053 }
3054 KSM_ATTR_RO(pages_shared);
3055
3056 static ssize_t pages_sharing_show(struct kobject *kobj,
3057                                   struct kobj_attribute *attr, char *buf)
3058 {
3059         return sysfs_emit(buf, "%lu\n", ksm_pages_sharing);
3060 }
3061 KSM_ATTR_RO(pages_sharing);
3062
3063 static ssize_t pages_unshared_show(struct kobject *kobj,
3064                                    struct kobj_attribute *attr, char *buf)
3065 {
3066         return sysfs_emit(buf, "%lu\n", ksm_pages_unshared);
3067 }
3068 KSM_ATTR_RO(pages_unshared);
3069
3070 static ssize_t pages_volatile_show(struct kobject *kobj,
3071                                    struct kobj_attribute *attr, char *buf)
3072 {
3073         long ksm_pages_volatile;
3074
3075         ksm_pages_volatile = ksm_rmap_items - ksm_pages_shared
3076                                 - ksm_pages_sharing - ksm_pages_unshared;
3077         /*
3078          * It was not worth any locking to calculate that statistic,
3079          * but it might therefore sometimes be negative: conceal that.
3080          */
3081         if (ksm_pages_volatile < 0)
3082                 ksm_pages_volatile = 0;
3083         return sysfs_emit(buf, "%ld\n", ksm_pages_volatile);
3084 }
3085 KSM_ATTR_RO(pages_volatile);
3086
3087 static ssize_t stable_node_dups_show(struct kobject *kobj,
3088                                      struct kobj_attribute *attr, char *buf)
3089 {
3090         return sysfs_emit(buf, "%lu\n", ksm_stable_node_dups);
3091 }
3092 KSM_ATTR_RO(stable_node_dups);
3093
3094 static ssize_t stable_node_chains_show(struct kobject *kobj,
3095                                        struct kobj_attribute *attr, char *buf)
3096 {
3097         return sysfs_emit(buf, "%lu\n", ksm_stable_node_chains);
3098 }
3099 KSM_ATTR_RO(stable_node_chains);
3100
3101 static ssize_t
3102 stable_node_chains_prune_millisecs_show(struct kobject *kobj,
3103                                         struct kobj_attribute *attr,
3104                                         char *buf)
3105 {
3106         return sysfs_emit(buf, "%u\n", ksm_stable_node_chains_prune_millisecs);
3107 }
3108
3109 static ssize_t
3110 stable_node_chains_prune_millisecs_store(struct kobject *kobj,
3111                                          struct kobj_attribute *attr,
3112                                          const char *buf, size_t count)
3113 {
3114         unsigned long msecs;
3115         int err;
3116
3117         err = kstrtoul(buf, 10, &msecs);
3118         if (err || msecs > UINT_MAX)
3119                 return -EINVAL;
3120
3121         ksm_stable_node_chains_prune_millisecs = msecs;
3122
3123         return count;
3124 }
3125 KSM_ATTR(stable_node_chains_prune_millisecs);
3126
3127 static ssize_t full_scans_show(struct kobject *kobj,
3128                                struct kobj_attribute *attr, char *buf)
3129 {
3130         return sysfs_emit(buf, "%lu\n", ksm_scan.seqnr);
3131 }
3132 KSM_ATTR_RO(full_scans);
3133
3134 static struct attribute *ksm_attrs[] = {
3135         &sleep_millisecs_attr.attr,
3136         &pages_to_scan_attr.attr,
3137         &run_attr.attr,
3138         &pages_shared_attr.attr,
3139         &pages_sharing_attr.attr,
3140         &pages_unshared_attr.attr,
3141         &pages_volatile_attr.attr,
3142         &full_scans_attr.attr,
3143 #ifdef CONFIG_NUMA
3144         &merge_across_nodes_attr.attr,
3145 #endif
3146         &max_page_sharing_attr.attr,
3147         &stable_node_chains_attr.attr,
3148         &stable_node_dups_attr.attr,
3149         &stable_node_chains_prune_millisecs_attr.attr,
3150         &use_zero_pages_attr.attr,
3151         NULL,
3152 };
3153
3154 static const struct attribute_group ksm_attr_group = {
3155         .attrs = ksm_attrs,
3156         .name = "ksm",
3157 };
3158 #endif /* CONFIG_SYSFS */
3159
3160 static int __init ksm_init(void)
3161 {
3162         struct task_struct *ksm_thread;
3163         int err;
3164
3165         /* The correct value depends on page size and endianness */
3166         zero_checksum = calc_checksum(ZERO_PAGE(0));
3167         /* Default to false for backwards compatibility */
3168         ksm_use_zero_pages = false;
3169
3170         err = ksm_slab_init();
3171         if (err)
3172                 goto out;
3173
3174         ksm_thread = kthread_run(ksm_scan_thread, NULL, "ksmd");
3175         if (IS_ERR(ksm_thread)) {
3176                 pr_err("ksm: creating kthread failed\n");
3177                 err = PTR_ERR(ksm_thread);
3178                 goto out_free;
3179         }
3180
3181 #ifdef CONFIG_SYSFS
3182         err = sysfs_create_group(mm_kobj, &ksm_attr_group);
3183         if (err) {
3184                 pr_err("ksm: register sysfs failed\n");
3185                 kthread_stop(ksm_thread);
3186                 goto out_free;
3187         }
3188 #else
3189         ksm_run = KSM_RUN_MERGE;        /* no way for user to start it */
3190
3191 #endif /* CONFIG_SYSFS */
3192
3193 #ifdef CONFIG_MEMORY_HOTREMOVE
3194         /* There is no significance to this priority 100 */
3195         hotplug_memory_notifier(ksm_memory_callback, 100);
3196 #endif
3197         return 0;
3198
3199 out_free:
3200         ksm_slab_free();
3201 out:
3202         return err;
3203 }
3204 subsys_initcall(ksm_init);