mm/mapping_dirty_helpers.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/pagewalk.h>
   3 #include <linux/hugetlb.h>
   4 #include <linux/bitops.h>
   5 #include <linux/mmu_notifier.h>
   6 #include <asm/cacheflush.h>
   7 #include <asm/tlbflush.h>
   8
   9 /**
  10  * struct wp_walk - Private struct for pagetable walk callbacks
  11  * @range: Range for mmu notifiers
  12  * @tlbflush_start: Address of first modified pte
  13  * @tlbflush_end: Address of last modified pte + 1
  14  * @total: Total number of modified ptes
  15  */
  16 struct wp_walk {
  17         struct mmu_notifier_range range;
  18         unsigned long tlbflush_start;
  19         unsigned long tlbflush_end;
  20         unsigned long total;
  21 };
  22
  23 /**
  24  * wp_pte - Write-protect a pte
  25  * @pte: Pointer to the pte
  26  * @addr: The start of protecting virtual address
  27  * @end: The end of protecting virtual address
  28  * @walk: pagetable walk callback argument
  29  *
  30  * The function write-protects a pte and records the range in
  31  * virtual address space of touched ptes for efficient range TLB flushes.
  32  */
  33 static int wp_pte(pte_t *pte, unsigned long addr, unsigned long end,
  34                   struct mm_walk *walk)
  35 {
  36         struct wp_walk *wpwalk = walk->private;
  37         pte_t ptent = *pte;
  38
  39         if (pte_write(ptent)) {
  40                 pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
  41
  42                 ptent = pte_wrprotect(old_pte);
  43                 ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
  44                 wpwalk->total++;
  45                 wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
  46                 wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
  47                                            addr + PAGE_SIZE);
  48         }
  49
  50         return 0;
  51 }
  52
  53 /**
  54  * struct clean_walk - Private struct for the clean_record_pte function.
  55  * @base: struct wp_walk we derive from
  56  * @bitmap_pgoff: Address_space Page offset of the first bit in @bitmap
  57  * @bitmap: Bitmap with one bit for each page offset in the address_space range
  58  * covered.
  59  * @start: Address_space page offset of first modified pte relative
  60  * to @bitmap_pgoff
  61  * @end: Address_space page offset of last modified pte relative
  62  * to @bitmap_pgoff
  63  */
  64 struct clean_walk {
  65         struct wp_walk base;
  66         pgoff_t bitmap_pgoff;
  67         unsigned long *bitmap;
  68         pgoff_t start;
  69         pgoff_t end;
  70 };
  71
  72 #define to_clean_walk(_wpwalk) container_of(_wpwalk, struct clean_walk, base)
  73
  74 /**
  75  * clean_record_pte - Clean a pte and record its address space offset in a
  76  * bitmap
  77  * @pte: Pointer to the pte
  78  * @addr: The start of virtual address to be clean
  79  * @end: The end of virtual address to be clean
  80  * @walk: pagetable walk callback argument
  81  *
  82  * The function cleans a pte and records the range in
  83  * virtual address space of touched ptes for efficient TLB flushes.
  84  * It also records dirty ptes in a bitmap representing page offsets
  85  * in the address_space, as well as the first and last of the bits
  86  * touched.
  87  */
  88 static int clean_record_pte(pte_t *pte, unsigned long addr,
  89                             unsigned long end, struct mm_walk *walk)
  90 {
  91         struct wp_walk *wpwalk = walk->private;
  92         struct clean_walk *cwalk = to_clean_walk(wpwalk);
  93         pte_t ptent = *pte;
  94
  95         if (pte_dirty(ptent)) {
  96                 pgoff_t pgoff = ((addr - walk->vma->vm_start) >> PAGE_SHIFT) +
  97                         walk->vma->vm_pgoff - cwalk->bitmap_pgoff;
  98                 pte_t old_pte = ptep_modify_prot_start(walk->vma, addr, pte);
  99
 100                 ptent = pte_mkclean(old_pte);
 101                 ptep_modify_prot_commit(walk->vma, addr, pte, old_pte, ptent);
 102
 103                 wpwalk->total++;
 104                 wpwalk->tlbflush_start = min(wpwalk->tlbflush_start, addr);
 105                 wpwalk->tlbflush_end = max(wpwalk->tlbflush_end,
 106                                            addr + PAGE_SIZE);
 107
 108                 __set_bit(pgoff, cwalk->bitmap);
 109                 cwalk->start = min(cwalk->start, pgoff);
 110                 cwalk->end = max(cwalk->end, pgoff + 1);
 111         }
 112
 113         return 0;
 114 }
 115
 116 /*
 117  * wp_clean_pmd_entry - The pagewalk pmd callback.
 118  *
 119  * Dirty-tracking should take place on the PTE level, so
 120  * WARN() if encountering a dirty huge pmd.
 121  * Furthermore, never split huge pmds, since that currently
 122  * causes dirty info loss. The pagefault handler should do
 123  * that if needed.
 124  */
 125 static int wp_clean_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long end,
 126                               struct mm_walk *walk)
 127 {
 128         pmd_t pmdval = pmd_read_atomic(pmd);
 129
 130         if (!pmd_trans_unstable(&pmdval))
 131                 return 0;
 132
 133         if (pmd_none(pmdval)) {
 134                 walk->action = ACTION_AGAIN;
 135                 return 0;
 136         }
 137
 138         /* Huge pmd, present or migrated */
 139         walk->action = ACTION_CONTINUE;
 140         if (pmd_trans_huge(pmdval) || pmd_devmap(pmdval))
 141                 WARN_ON(pmd_write(pmdval) || pmd_dirty(pmdval));
 142
 143         return 0;
 144 }
 145
 146 /*
 147  * wp_clean_pud_entry - The pagewalk pud callback.
 148  *
 149  * Dirty-tracking should take place on the PTE level, so
 150  * WARN() if encountering a dirty huge puds.
 151  * Furthermore, never split huge puds, since that currently
 152  * causes dirty info loss. The pagefault handler should do
 153  * that if needed.
 154  */
 155 static int wp_clean_pud_entry(pud_t *pud, unsigned long addr, unsigned long end,
 156                               struct mm_walk *walk)
 157 {
 158         pud_t pudval = READ_ONCE(*pud);
 159
 160         if (!pud_trans_unstable(&pudval))
 161                 return 0;
 162
 163         if (pud_none(pudval)) {
 164                 walk->action = ACTION_AGAIN;
 165                 return 0;
 166         }
 167
 168         /* Huge pud */
 169         walk->action = ACTION_CONTINUE;
 170         if (pud_trans_huge(pudval) || pud_devmap(pudval))
 171                 WARN_ON(pud_write(pudval) || pud_dirty(pudval));
 172
 173         return 0;
 174 }
 175
 176 /*
 177  * wp_clean_pre_vma - The pagewalk pre_vma callback.
 178  *
 179  * The pre_vma callback performs the cache flush, stages the tlb flush
 180  * and calls the necessary mmu notifiers.
 181  */
 182 static int wp_clean_pre_vma(unsigned long start, unsigned long end,
 183                             struct mm_walk *walk)
 184 {
 185         struct wp_walk *wpwalk = walk->private;
 186
 187         wpwalk->tlbflush_start = end;
 188         wpwalk->tlbflush_end = start;
 189
 190         mmu_notifier_range_init(&wpwalk->range, MMU_NOTIFY_PROTECTION_PAGE, 0,
 191                                 walk->vma, walk->mm, start, end);
 192         mmu_notifier_invalidate_range_start(&wpwalk->range);
 193         flush_cache_range(walk->vma, start, end);
 194
 195         /*
 196          * We're not using tlb_gather_mmu() since typically
 197          * only a small subrange of PTEs are affected, whereas
 198          * tlb_gather_mmu() records the full range.
 199          */
 200         inc_tlb_flush_pending(walk->mm);
 201
 202         return 0;
 203 }
 204
 205 /*
 206  * wp_clean_post_vma - The pagewalk post_vma callback.
 207  *
 208  * The post_vma callback performs the tlb flush and calls necessary mmu
 209  * notifiers.
 210  */
 211 static void wp_clean_post_vma(struct mm_walk *walk)
 212 {
 213         struct wp_walk *wpwalk = walk->private;
 214
 215         if (mm_tlb_flush_nested(walk->mm))
 216                 flush_tlb_range(walk->vma, wpwalk->range.start,
 217                                 wpwalk->range.end);
 218         else if (wpwalk->tlbflush_end > wpwalk->tlbflush_start)
 219                 flush_tlb_range(walk->vma, wpwalk->tlbflush_start,
 220                                 wpwalk->tlbflush_end);
 221
 222         mmu_notifier_invalidate_range_end(&wpwalk->range);
 223         dec_tlb_flush_pending(walk->mm);
 224 }
 225
 226 /*
 227  * wp_clean_test_walk - The pagewalk test_walk callback.
 228  *
 229  * Won't perform dirty-tracking on COW, read-only or HUGETLB vmas.
 230  */
 231 static int wp_clean_test_walk(unsigned long start, unsigned long end,
 232                               struct mm_walk *walk)
 233 {
 234         unsigned long vm_flags = READ_ONCE(walk->vma->vm_flags);
 235
 236         /* Skip non-applicable VMAs */
 237         if ((vm_flags & (VM_SHARED | VM_MAYWRITE | VM_HUGETLB)) !=
 238             (VM_SHARED | VM_MAYWRITE))
 239                 return 1;
 240
 241         return 0;
 242 }
 243
 244 static const struct mm_walk_ops clean_walk_ops = {
 245         .pte_entry = clean_record_pte,
 246         .pmd_entry = wp_clean_pmd_entry,
 247         .pud_entry = wp_clean_pud_entry,
 248         .test_walk = wp_clean_test_walk,
 249         .pre_vma = wp_clean_pre_vma,
 250         .post_vma = wp_clean_post_vma
 251 };
 252
 253 static const struct mm_walk_ops wp_walk_ops = {
 254         .pte_entry = wp_pte,
 255         .pmd_entry = wp_clean_pmd_entry,
 256         .pud_entry = wp_clean_pud_entry,
 257         .test_walk = wp_clean_test_walk,
 258         .pre_vma = wp_clean_pre_vma,
 259         .post_vma = wp_clean_post_vma
 260 };
 261
 262 /**
 263  * wp_shared_mapping_range - Write-protect all ptes in an address space range
 264  * @mapping: The address_space we want to write protect
 265  * @first_index: The first page offset in the range
 266  * @nr: Number of incremental page offsets to cover
 267  *
 268  * Note: This function currently skips transhuge page-table entries, since
 269  * it's intended for dirty-tracking on the PTE level. It will warn on
 270  * encountering transhuge write-enabled entries, though, and can easily be
 271  * extended to handle them as well.
 272  *
 273  * Return: The number of ptes actually write-protected. Note that
 274  * already write-protected ptes are not counted.
 275  */
 276 unsigned long wp_shared_mapping_range(struct address_space *mapping,
 277                                       pgoff_t first_index, pgoff_t nr)
 278 {
 279         struct wp_walk wpwalk = { .total = 0 };
 280
 281         i_mmap_lock_read(mapping);
 282         WARN_ON(walk_page_mapping(mapping, first_index, nr, &wp_walk_ops,
 283                                   &wpwalk));
 284         i_mmap_unlock_read(mapping);
 285
 286         return wpwalk.total;
 287 }
 288 EXPORT_SYMBOL_GPL(wp_shared_mapping_range);
 289
 290 /**
 291  * clean_record_shared_mapping_range - Clean and record all ptes in an
 292  * address space range
 293  * @mapping: The address_space we want to clean
 294  * @first_index: The first page offset in the range
 295  * @nr: Number of incremental page offsets to cover
 296  * @bitmap_pgoff: The page offset of the first bit in @bitmap
 297  * @bitmap: Pointer to a bitmap of at least @nr bits. The bitmap needs to
 298  * cover the whole range @first_index..@first_index + @nr.
 299  * @start: Pointer to number of the first set bit in @bitmap.
 300  * is modified as new bits are set by the function.
 301  * @end: Pointer to the number of the last set bit in @bitmap.
 302  * none set. The value is modified as new bits are set by the function.
 303  *
 304  * Note: When this function returns there is no guarantee that a CPU has
 305  * not already dirtied new ptes. However it will not clean any ptes not
 306  * reported in the bitmap. The guarantees are as follows:
 307  * a) All ptes dirty when the function starts executing will end up recorded
 308  *    in the bitmap.
 309  * b) All ptes dirtied after that will either remain dirty, be recorded in the
 310  *    bitmap or both.
 311  *
 312  * If a caller needs to make sure all dirty ptes are picked up and none
 313  * additional are added, it first needs to write-protect the address-space
 314  * range and make sure new writers are blocked in page_mkwrite() or
 315  * pfn_mkwrite(). And then after a TLB flush following the write-protection
 316  * pick up all dirty bits.
 317  *
 318  * Note: This function currently skips transhuge page-table entries, since
 319  * it's intended for dirty-tracking on the PTE level. It will warn on
 320  * encountering transhuge dirty entries, though, and can easily be extended
 321  * to handle them as well.
 322  *
 323  * Return: The number of dirty ptes actually cleaned.
 324  */
 325 unsigned long clean_record_shared_mapping_range(struct address_space *mapping,
 326                                                 pgoff_t first_index, pgoff_t nr,
 327                                                 pgoff_t bitmap_pgoff,
 328                                                 unsigned long *bitmap,
 329                                                 pgoff_t *start,
 330                                                 pgoff_t *end)
 331 {
 332         bool none_set = (*start >= *end);
 333         struct clean_walk cwalk = {
 334                 .base = { .total = 0 },
 335                 .bitmap_pgoff = bitmap_pgoff,
 336                 .bitmap = bitmap,
 337                 .start = none_set ? nr : *start,
 338                 .end = none_set ? 0 : *end,
 339         };
 340
 341         i_mmap_lock_read(mapping);
 342         WARN_ON(walk_page_mapping(mapping, first_index, nr, &clean_walk_ops,
 343                                   &cwalk.base));
 344         i_mmap_unlock_read(mapping);
 345
 346         *start = cwalk.start;
 347         *end = cwalk.end;
 348
 349         return cwalk.base.total;
 350 }
 351 EXPORT_SYMBOL_GPL(clean_record_shared_mapping_range);