4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 * Copyright (C) 2008-2009 Red Hat, Inc.
6 * Copyright (C) 2015 Red Hat, Inc.
8 * This work is licensed under the terms of the GNU GPL, version 2. See
9 * the COPYING file in the top-level directory.
11 * Some part derived from fs/eventfd.c (anon inode setup) and
12 * mm/ksm.c (mm hashing).
15 #include <linux/list.h>
16 #include <linux/hashtable.h>
17 #include <linux/sched/signal.h>
18 #include <linux/sched/mm.h>
20 #include <linux/poll.h>
21 #include <linux/slab.h>
22 #include <linux/seq_file.h>
23 #include <linux/file.h>
24 #include <linux/bug.h>
25 #include <linux/anon_inodes.h>
26 #include <linux/syscalls.h>
27 #include <linux/userfaultfd_k.h>
28 #include <linux/mempolicy.h>
29 #include <linux/ioctl.h>
30 #include <linux/security.h>
31 #include <linux/hugetlb.h>
33 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
35 enum userfaultfd_state {
41 * Start with fault_pending_wqh and fault_wqh so they're more likely
42 * to be in the same cacheline.
44 struct userfaultfd_ctx {
45 /* waitqueue head for the pending (i.e. not read) userfaults */
46 wait_queue_head_t fault_pending_wqh;
47 /* waitqueue head for the userfaults */
48 wait_queue_head_t fault_wqh;
49 /* waitqueue head for the pseudo fd to wakeup poll/read */
50 wait_queue_head_t fd_wqh;
51 /* waitqueue head for events */
52 wait_queue_head_t event_wqh;
53 /* a refile sequence protected by fault_pending_wqh lock */
54 struct seqcount refile_seq;
55 /* pseudo fd refcounting */
57 /* userfaultfd syscall flags */
59 /* features requested from the userspace */
60 unsigned int features;
62 enum userfaultfd_state state;
65 /* mm with one ore more vmas attached to this userfaultfd_ctx */
69 struct userfaultfd_fork_ctx {
70 struct userfaultfd_ctx *orig;
71 struct userfaultfd_ctx *new;
72 struct list_head list;
75 struct userfaultfd_unmap_ctx {
76 struct userfaultfd_ctx *ctx;
79 struct list_head list;
82 struct userfaultfd_wait_queue {
84 wait_queue_entry_t wq;
85 struct userfaultfd_ctx *ctx;
89 struct userfaultfd_wake_range {
94 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
95 int wake_flags, void *key)
97 struct userfaultfd_wake_range *range = key;
99 struct userfaultfd_wait_queue *uwq;
100 unsigned long start, len;
102 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
104 /* len == 0 means wake all */
105 start = range->start;
107 if (len && (start > uwq->msg.arg.pagefault.address ||
108 start + len <= uwq->msg.arg.pagefault.address))
110 WRITE_ONCE(uwq->waken, true);
112 * The Program-Order guarantees provided by the scheduler
113 * ensure uwq->waken is visible before the task is woken.
115 ret = wake_up_state(wq->private, mode);
118 * Wake only once, autoremove behavior.
120 * After the effect of list_del_init is visible to the other
121 * CPUs, the waitqueue may disappear from under us, see the
122 * !list_empty_careful() in handle_userfault().
124 * try_to_wake_up() has an implicit smp_mb(), and the
125 * wq->private is read before calling the extern function
126 * "wake_up_state" (which in turns calls try_to_wake_up).
128 list_del_init(&wq->entry);
135 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
137 * @ctx: [in] Pointer to the userfaultfd context.
139 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
141 if (!atomic_inc_not_zero(&ctx->refcount))
146 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
148 * @ctx: [in] Pointer to userfaultfd context.
150 * The userfaultfd context reference must have been previously acquired either
151 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
153 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
155 if (atomic_dec_and_test(&ctx->refcount)) {
156 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
157 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
158 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
159 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
160 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
161 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
162 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
163 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
165 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
169 static inline void msg_init(struct uffd_msg *msg)
171 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
173 * Must use memset to zero out the paddings or kernel data is
174 * leaked to userland.
176 memset(msg, 0, sizeof(struct uffd_msg));
179 static inline struct uffd_msg userfault_msg(unsigned long address,
181 unsigned long reason,
182 unsigned int features)
186 msg.event = UFFD_EVENT_PAGEFAULT;
187 msg.arg.pagefault.address = address;
188 if (flags & FAULT_FLAG_WRITE)
190 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
191 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
192 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
193 * was a read fault, otherwise if set it means it's
196 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
197 if (reason & VM_UFFD_WP)
199 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
200 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
201 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
202 * a missing fault, otherwise if set it means it's a
203 * write protect fault.
205 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
206 if (features & UFFD_FEATURE_THREAD_ID)
207 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
211 #ifdef CONFIG_HUGETLB_PAGE
213 * Same functionality as userfaultfd_must_wait below with modifications for
216 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
217 struct vm_area_struct *vma,
218 unsigned long address,
220 unsigned long reason)
222 struct mm_struct *mm = ctx->mm;
226 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
228 pte = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
235 * Lockless access: we're in a wait_event so it's ok if it
238 if (huge_pte_none(*pte))
240 if (!huge_pte_write(*pte) && (reason & VM_UFFD_WP))
246 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
247 struct vm_area_struct *vma,
248 unsigned long address,
250 unsigned long reason)
252 return false; /* should never get here */
254 #endif /* CONFIG_HUGETLB_PAGE */
257 * Verify the pagetables are still not ok after having reigstered into
258 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
259 * userfault that has already been resolved, if userfaultfd_read and
260 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
263 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
264 unsigned long address,
266 unsigned long reason)
268 struct mm_struct *mm = ctx->mm;
276 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
278 pgd = pgd_offset(mm, address);
279 if (!pgd_present(*pgd))
281 p4d = p4d_offset(pgd, address);
282 if (!p4d_present(*p4d))
284 pud = pud_offset(p4d, address);
285 if (!pud_present(*pud))
287 pmd = pmd_offset(pud, address);
289 * READ_ONCE must function as a barrier with narrower scope
290 * and it must be equivalent to:
291 * _pmd = *pmd; barrier();
293 * This is to deal with the instability (as in
294 * pmd_trans_unstable) of the pmd.
296 _pmd = READ_ONCE(*pmd);
297 if (!pmd_present(_pmd))
301 if (pmd_trans_huge(_pmd))
305 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
306 * and use the standard pte_offset_map() instead of parsing _pmd.
308 pte = pte_offset_map(pmd, address);
310 * Lockless access: we're in a wait_event so it's ok if it
322 * The locking rules involved in returning VM_FAULT_RETRY depending on
323 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
324 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
325 * recommendation in __lock_page_or_retry is not an understatement.
327 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
328 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
331 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
332 * set, VM_FAULT_RETRY can still be returned if and only if there are
333 * fatal_signal_pending()s, and the mmap_sem must be released before
336 int handle_userfault(struct vm_fault *vmf, unsigned long reason)
338 struct mm_struct *mm = vmf->vma->vm_mm;
339 struct userfaultfd_ctx *ctx;
340 struct userfaultfd_wait_queue uwq;
342 bool must_wait, return_to_userland;
345 ret = VM_FAULT_SIGBUS;
348 * We don't do userfault handling for the final child pid update.
350 * We also don't do userfault handling during
351 * coredumping. hugetlbfs has the special
352 * follow_hugetlb_page() to skip missing pages in the
353 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
354 * the no_page_table() helper in follow_page_mask(), but the
355 * shmem_vm_ops->fault method is invoked even during
356 * coredumping without mmap_sem and it ends up here.
358 if (current->flags & (PF_EXITING|PF_DUMPCORE))
362 * Coredumping runs without mmap_sem so we can only check that
363 * the mmap_sem is held, if PF_DUMPCORE was not set.
365 WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
367 ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
371 BUG_ON(ctx->mm != mm);
373 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
374 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
376 if (ctx->features & UFFD_FEATURE_SIGBUS)
380 * If it's already released don't get it. This avoids to loop
381 * in __get_user_pages if userfaultfd_release waits on the
382 * caller of handle_userfault to release the mmap_sem.
384 if (unlikely(ACCESS_ONCE(ctx->released)))
388 * Check that we can return VM_FAULT_RETRY.
390 * NOTE: it should become possible to return VM_FAULT_RETRY
391 * even if FAULT_FLAG_TRIED is set without leading to gup()
392 * -EBUSY failures, if the userfaultfd is to be extended for
393 * VM_UFFD_WP tracking and we intend to arm the userfault
394 * without first stopping userland access to the memory. For
395 * VM_UFFD_MISSING userfaults this is enough for now.
397 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
399 * Validate the invariant that nowait must allow retry
400 * to be sure not to return SIGBUS erroneously on
401 * nowait invocations.
403 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
404 #ifdef CONFIG_DEBUG_VM
405 if (printk_ratelimit()) {
407 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
416 * Handle nowait, not much to do other than tell it to retry
419 ret = VM_FAULT_RETRY;
420 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
423 /* take the reference before dropping the mmap_sem */
424 userfaultfd_ctx_get(ctx);
426 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
427 uwq.wq.private = current;
428 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
434 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
435 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
436 blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
439 spin_lock(&ctx->fault_pending_wqh.lock);
441 * After the __add_wait_queue the uwq is visible to userland
442 * through poll/read().
444 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
446 * The smp_mb() after __set_current_state prevents the reads
447 * following the spin_unlock to happen before the list_add in
450 set_current_state(blocking_state);
451 spin_unlock(&ctx->fault_pending_wqh.lock);
453 if (!is_vm_hugetlb_page(vmf->vma))
454 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
457 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
460 up_read(&mm->mmap_sem);
462 if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
463 (return_to_userland ? !signal_pending(current) :
464 !fatal_signal_pending(current)))) {
465 wake_up_poll(&ctx->fd_wqh, POLLIN);
467 ret |= VM_FAULT_MAJOR;
470 * False wakeups can orginate even from rwsem before
471 * up_read() however userfaults will wait either for a
472 * targeted wakeup on the specific uwq waitqueue from
473 * wake_userfault() or for signals or for uffd
476 while (!READ_ONCE(uwq.waken)) {
478 * This needs the full smp_store_mb()
479 * guarantee as the state write must be
480 * visible to other CPUs before reading
481 * uwq.waken from other CPUs.
483 set_current_state(blocking_state);
484 if (READ_ONCE(uwq.waken) ||
485 READ_ONCE(ctx->released) ||
486 (return_to_userland ? signal_pending(current) :
487 fatal_signal_pending(current)))
493 __set_current_state(TASK_RUNNING);
495 if (return_to_userland) {
496 if (signal_pending(current) &&
497 !fatal_signal_pending(current)) {
499 * If we got a SIGSTOP or SIGCONT and this is
500 * a normal userland page fault, just let
501 * userland return so the signal will be
502 * handled and gdb debugging works. The page
503 * fault code immediately after we return from
504 * this function is going to release the
505 * mmap_sem and it's not depending on it
506 * (unlike gup would if we were not to return
509 * If a fatal signal is pending we still take
510 * the streamlined VM_FAULT_RETRY failure path
511 * and there's no need to retake the mmap_sem
514 down_read(&mm->mmap_sem);
515 ret = VM_FAULT_NOPAGE;
520 * Here we race with the list_del; list_add in
521 * userfaultfd_ctx_read(), however because we don't ever run
522 * list_del_init() to refile across the two lists, the prev
523 * and next pointers will never point to self. list_add also
524 * would never let any of the two pointers to point to
525 * self. So list_empty_careful won't risk to see both pointers
526 * pointing to self at any time during the list refile. The
527 * only case where list_del_init() is called is the full
528 * removal in the wake function and there we don't re-list_add
529 * and it's fine not to block on the spinlock. The uwq on this
530 * kernel stack can be released after the list_del_init.
532 if (!list_empty_careful(&uwq.wq.entry)) {
533 spin_lock(&ctx->fault_pending_wqh.lock);
535 * No need of list_del_init(), the uwq on the stack
536 * will be freed shortly anyway.
538 list_del(&uwq.wq.entry);
539 spin_unlock(&ctx->fault_pending_wqh.lock);
543 * ctx may go away after this if the userfault pseudo fd is
546 userfaultfd_ctx_put(ctx);
552 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
553 struct userfaultfd_wait_queue *ewq)
555 if (WARN_ON_ONCE(current->flags & PF_EXITING))
559 init_waitqueue_entry(&ewq->wq, current);
561 spin_lock(&ctx->event_wqh.lock);
563 * After the __add_wait_queue the uwq is visible to userland
564 * through poll/read().
566 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
568 set_current_state(TASK_KILLABLE);
569 if (ewq->msg.event == 0)
571 if (ACCESS_ONCE(ctx->released) ||
572 fatal_signal_pending(current)) {
573 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
574 if (ewq->msg.event == UFFD_EVENT_FORK) {
575 struct userfaultfd_ctx *new;
577 new = (struct userfaultfd_ctx *)
579 ewq->msg.arg.reserved.reserved1;
581 userfaultfd_ctx_put(new);
586 spin_unlock(&ctx->event_wqh.lock);
588 wake_up_poll(&ctx->fd_wqh, POLLIN);
591 spin_lock(&ctx->event_wqh.lock);
593 __set_current_state(TASK_RUNNING);
594 spin_unlock(&ctx->event_wqh.lock);
597 * ctx may go away after this if the userfault pseudo fd is
601 userfaultfd_ctx_put(ctx);
604 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
605 struct userfaultfd_wait_queue *ewq)
608 wake_up_locked(&ctx->event_wqh);
609 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
612 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
614 struct userfaultfd_ctx *ctx = NULL, *octx;
615 struct userfaultfd_fork_ctx *fctx;
617 octx = vma->vm_userfaultfd_ctx.ctx;
618 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
619 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
620 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
624 list_for_each_entry(fctx, fcs, list)
625 if (fctx->orig == octx) {
631 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
635 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
641 atomic_set(&ctx->refcount, 1);
642 ctx->flags = octx->flags;
643 ctx->state = UFFD_STATE_RUNNING;
644 ctx->features = octx->features;
645 ctx->released = false;
646 ctx->mm = vma->vm_mm;
647 atomic_inc(&ctx->mm->mm_count);
649 userfaultfd_ctx_get(octx);
652 list_add_tail(&fctx->list, fcs);
655 vma->vm_userfaultfd_ctx.ctx = ctx;
659 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
661 struct userfaultfd_ctx *ctx = fctx->orig;
662 struct userfaultfd_wait_queue ewq;
666 ewq.msg.event = UFFD_EVENT_FORK;
667 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
669 userfaultfd_event_wait_completion(ctx, &ewq);
672 void dup_userfaultfd_complete(struct list_head *fcs)
674 struct userfaultfd_fork_ctx *fctx, *n;
676 list_for_each_entry_safe(fctx, n, fcs, list) {
678 list_del(&fctx->list);
683 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
684 struct vm_userfaultfd_ctx *vm_ctx)
686 struct userfaultfd_ctx *ctx;
688 ctx = vma->vm_userfaultfd_ctx.ctx;
689 if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
691 userfaultfd_ctx_get(ctx);
695 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
696 unsigned long from, unsigned long to,
699 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
700 struct userfaultfd_wait_queue ewq;
705 if (to & ~PAGE_MASK) {
706 userfaultfd_ctx_put(ctx);
712 ewq.msg.event = UFFD_EVENT_REMAP;
713 ewq.msg.arg.remap.from = from;
714 ewq.msg.arg.remap.to = to;
715 ewq.msg.arg.remap.len = len;
717 userfaultfd_event_wait_completion(ctx, &ewq);
720 bool userfaultfd_remove(struct vm_area_struct *vma,
721 unsigned long start, unsigned long end)
723 struct mm_struct *mm = vma->vm_mm;
724 struct userfaultfd_ctx *ctx;
725 struct userfaultfd_wait_queue ewq;
727 ctx = vma->vm_userfaultfd_ctx.ctx;
728 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
731 userfaultfd_ctx_get(ctx);
732 up_read(&mm->mmap_sem);
736 ewq.msg.event = UFFD_EVENT_REMOVE;
737 ewq.msg.arg.remove.start = start;
738 ewq.msg.arg.remove.end = end;
740 userfaultfd_event_wait_completion(ctx, &ewq);
745 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
746 unsigned long start, unsigned long end)
748 struct userfaultfd_unmap_ctx *unmap_ctx;
750 list_for_each_entry(unmap_ctx, unmaps, list)
751 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
752 unmap_ctx->end == end)
758 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
759 unsigned long start, unsigned long end,
760 struct list_head *unmaps)
762 for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
763 struct userfaultfd_unmap_ctx *unmap_ctx;
764 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
766 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
767 has_unmap_ctx(ctx, unmaps, start, end))
770 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
774 userfaultfd_ctx_get(ctx);
775 unmap_ctx->ctx = ctx;
776 unmap_ctx->start = start;
777 unmap_ctx->end = end;
778 list_add_tail(&unmap_ctx->list, unmaps);
784 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
786 struct userfaultfd_unmap_ctx *ctx, *n;
787 struct userfaultfd_wait_queue ewq;
789 list_for_each_entry_safe(ctx, n, uf, list) {
792 ewq.msg.event = UFFD_EVENT_UNMAP;
793 ewq.msg.arg.remove.start = ctx->start;
794 ewq.msg.arg.remove.end = ctx->end;
796 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
798 list_del(&ctx->list);
803 static int userfaultfd_release(struct inode *inode, struct file *file)
805 struct userfaultfd_ctx *ctx = file->private_data;
806 struct mm_struct *mm = ctx->mm;
807 struct vm_area_struct *vma, *prev;
808 /* len == 0 means wake all */
809 struct userfaultfd_wake_range range = { .len = 0, };
810 unsigned long new_flags;
812 ACCESS_ONCE(ctx->released) = true;
814 if (!mmget_not_zero(mm))
818 * Flush page faults out of all CPUs. NOTE: all page faults
819 * must be retried without returning VM_FAULT_SIGBUS if
820 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
821 * changes while handle_userfault released the mmap_sem. So
822 * it's critical that released is set to true (above), before
823 * taking the mmap_sem for writing.
825 down_write(&mm->mmap_sem);
827 for (vma = mm->mmap; vma; vma = vma->vm_next) {
829 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
830 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
831 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
835 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
836 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
837 new_flags, vma->anon_vma,
838 vma->vm_file, vma->vm_pgoff,
845 vma->vm_flags = new_flags;
846 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
848 up_write(&mm->mmap_sem);
852 * After no new page faults can wait on this fault_*wqh, flush
853 * the last page faults that may have been already waiting on
856 spin_lock(&ctx->fault_pending_wqh.lock);
857 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
858 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
859 spin_unlock(&ctx->fault_pending_wqh.lock);
861 /* Flush pending events that may still wait on event_wqh */
862 wake_up_all(&ctx->event_wqh);
864 wake_up_poll(&ctx->fd_wqh, POLLHUP);
865 userfaultfd_ctx_put(ctx);
869 /* fault_pending_wqh.lock must be hold by the caller */
870 static inline struct userfaultfd_wait_queue *find_userfault_in(
871 wait_queue_head_t *wqh)
873 wait_queue_entry_t *wq;
874 struct userfaultfd_wait_queue *uwq;
876 VM_BUG_ON(!spin_is_locked(&wqh->lock));
879 if (!waitqueue_active(wqh))
881 /* walk in reverse to provide FIFO behavior to read userfaults */
882 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
883 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
888 static inline struct userfaultfd_wait_queue *find_userfault(
889 struct userfaultfd_ctx *ctx)
891 return find_userfault_in(&ctx->fault_pending_wqh);
894 static inline struct userfaultfd_wait_queue *find_userfault_evt(
895 struct userfaultfd_ctx *ctx)
897 return find_userfault_in(&ctx->event_wqh);
900 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
902 struct userfaultfd_ctx *ctx = file->private_data;
905 poll_wait(file, &ctx->fd_wqh, wait);
907 switch (ctx->state) {
908 case UFFD_STATE_WAIT_API:
910 case UFFD_STATE_RUNNING:
912 * poll() never guarantees that read won't block.
913 * userfaults can be waken before they're read().
915 if (unlikely(!(file->f_flags & O_NONBLOCK)))
918 * lockless access to see if there are pending faults
919 * __pollwait last action is the add_wait_queue but
920 * the spin_unlock would allow the waitqueue_active to
921 * pass above the actual list_add inside
922 * add_wait_queue critical section. So use a full
923 * memory barrier to serialize the list_add write of
924 * add_wait_queue() with the waitqueue_active read
929 if (waitqueue_active(&ctx->fault_pending_wqh))
931 else if (waitqueue_active(&ctx->event_wqh))
941 static const struct file_operations userfaultfd_fops;
943 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
944 struct userfaultfd_ctx *new,
945 struct uffd_msg *msg)
949 unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS;
951 fd = get_unused_fd_flags(flags);
955 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new,
959 return PTR_ERR(file);
962 fd_install(fd, file);
963 msg->arg.reserved.reserved1 = 0;
964 msg->arg.fork.ufd = fd;
969 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
970 struct uffd_msg *msg)
973 DECLARE_WAITQUEUE(wait, current);
974 struct userfaultfd_wait_queue *uwq;
976 * Handling fork event requires sleeping operations, so
977 * we drop the event_wqh lock, then do these ops, then
978 * lock it back and wake up the waiter. While the lock is
979 * dropped the ewq may go away so we keep track of it
982 LIST_HEAD(fork_event);
983 struct userfaultfd_ctx *fork_nctx = NULL;
985 /* always take the fd_wqh lock before the fault_pending_wqh lock */
986 spin_lock(&ctx->fd_wqh.lock);
987 __add_wait_queue(&ctx->fd_wqh, &wait);
989 set_current_state(TASK_INTERRUPTIBLE);
990 spin_lock(&ctx->fault_pending_wqh.lock);
991 uwq = find_userfault(ctx);
994 * Use a seqcount to repeat the lockless check
995 * in wake_userfault() to avoid missing
996 * wakeups because during the refile both
997 * waitqueue could become empty if this is the
1000 write_seqcount_begin(&ctx->refile_seq);
1003 * The fault_pending_wqh.lock prevents the uwq
1004 * to disappear from under us.
1006 * Refile this userfault from
1007 * fault_pending_wqh to fault_wqh, it's not
1008 * pending anymore after we read it.
1010 * Use list_del() by hand (as
1011 * userfaultfd_wake_function also uses
1012 * list_del_init() by hand) to be sure nobody
1013 * changes __remove_wait_queue() to use
1014 * list_del_init() in turn breaking the
1015 * !list_empty_careful() check in
1016 * handle_userfault(). The uwq->wq.head list
1017 * must never be empty at any time during the
1018 * refile, or the waitqueue could disappear
1019 * from under us. The "wait_queue_head_t"
1020 * parameter of __remove_wait_queue() is unused
1023 list_del(&uwq->wq.entry);
1024 __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1026 write_seqcount_end(&ctx->refile_seq);
1028 /* careful to always initialize msg if ret == 0 */
1030 spin_unlock(&ctx->fault_pending_wqh.lock);
1034 spin_unlock(&ctx->fault_pending_wqh.lock);
1036 spin_lock(&ctx->event_wqh.lock);
1037 uwq = find_userfault_evt(ctx);
1041 if (uwq->msg.event == UFFD_EVENT_FORK) {
1042 fork_nctx = (struct userfaultfd_ctx *)
1044 uwq->msg.arg.reserved.reserved1;
1045 list_move(&uwq->wq.entry, &fork_event);
1046 spin_unlock(&ctx->event_wqh.lock);
1051 userfaultfd_event_complete(ctx, uwq);
1052 spin_unlock(&ctx->event_wqh.lock);
1056 spin_unlock(&ctx->event_wqh.lock);
1058 if (signal_pending(current)) {
1066 spin_unlock(&ctx->fd_wqh.lock);
1068 spin_lock(&ctx->fd_wqh.lock);
1070 __remove_wait_queue(&ctx->fd_wqh, &wait);
1071 __set_current_state(TASK_RUNNING);
1072 spin_unlock(&ctx->fd_wqh.lock);
1074 if (!ret && msg->event == UFFD_EVENT_FORK) {
1075 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1078 spin_lock(&ctx->event_wqh.lock);
1079 if (!list_empty(&fork_event)) {
1080 uwq = list_first_entry(&fork_event,
1083 list_del(&uwq->wq.entry);
1084 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1085 userfaultfd_event_complete(ctx, uwq);
1087 spin_unlock(&ctx->event_wqh.lock);
1094 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1095 size_t count, loff_t *ppos)
1097 struct userfaultfd_ctx *ctx = file->private_data;
1098 ssize_t _ret, ret = 0;
1099 struct uffd_msg msg;
1100 int no_wait = file->f_flags & O_NONBLOCK;
1102 if (ctx->state == UFFD_STATE_WAIT_API)
1106 if (count < sizeof(msg))
1107 return ret ? ret : -EINVAL;
1108 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1110 return ret ? ret : _ret;
1111 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1112 return ret ? ret : -EFAULT;
1115 count -= sizeof(msg);
1117 * Allow to read more than one fault at time but only
1118 * block if waiting for the very first one.
1120 no_wait = O_NONBLOCK;
1124 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1125 struct userfaultfd_wake_range *range)
1127 spin_lock(&ctx->fault_pending_wqh.lock);
1128 /* wake all in the range and autoremove */
1129 if (waitqueue_active(&ctx->fault_pending_wqh))
1130 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1132 if (waitqueue_active(&ctx->fault_wqh))
1133 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
1134 spin_unlock(&ctx->fault_pending_wqh.lock);
1137 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1138 struct userfaultfd_wake_range *range)
1144 * To be sure waitqueue_active() is not reordered by the CPU
1145 * before the pagetable update, use an explicit SMP memory
1146 * barrier here. PT lock release or up_read(mmap_sem) still
1147 * have release semantics that can allow the
1148 * waitqueue_active() to be reordered before the pte update.
1153 * Use waitqueue_active because it's very frequent to
1154 * change the address space atomically even if there are no
1155 * userfaults yet. So we take the spinlock only when we're
1156 * sure we've userfaults to wake.
1159 seq = read_seqcount_begin(&ctx->refile_seq);
1160 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1161 waitqueue_active(&ctx->fault_wqh);
1163 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1165 __wake_userfault(ctx, range);
1168 static __always_inline int validate_range(struct mm_struct *mm,
1169 __u64 start, __u64 len)
1171 __u64 task_size = mm->task_size;
1173 if (start & ~PAGE_MASK)
1175 if (len & ~PAGE_MASK)
1179 if (start < mmap_min_addr)
1181 if (start >= task_size)
1183 if (len > task_size - start)
1188 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1190 return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1194 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1197 struct mm_struct *mm = ctx->mm;
1198 struct vm_area_struct *vma, *prev, *cur;
1200 struct uffdio_register uffdio_register;
1201 struct uffdio_register __user *user_uffdio_register;
1202 unsigned long vm_flags, new_flags;
1205 unsigned long start, end, vma_end;
1207 user_uffdio_register = (struct uffdio_register __user *) arg;
1210 if (copy_from_user(&uffdio_register, user_uffdio_register,
1211 sizeof(uffdio_register)-sizeof(__u64)))
1215 if (!uffdio_register.mode)
1217 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1218 UFFDIO_REGISTER_MODE_WP))
1221 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1222 vm_flags |= VM_UFFD_MISSING;
1223 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1224 vm_flags |= VM_UFFD_WP;
1226 * FIXME: remove the below error constraint by
1227 * implementing the wprotect tracking mode.
1233 ret = validate_range(mm, uffdio_register.range.start,
1234 uffdio_register.range.len);
1238 start = uffdio_register.range.start;
1239 end = start + uffdio_register.range.len;
1242 if (!mmget_not_zero(mm))
1245 down_write(&mm->mmap_sem);
1246 vma = find_vma_prev(mm, start, &prev);
1250 /* check that there's at least one vma in the range */
1252 if (vma->vm_start >= end)
1256 * If the first vma contains huge pages, make sure start address
1257 * is aligned to huge page size.
1259 if (is_vm_hugetlb_page(vma)) {
1260 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1262 if (start & (vma_hpagesize - 1))
1267 * Search for not compatible vmas.
1270 basic_ioctls = false;
1271 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1274 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1275 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1277 /* check not compatible vmas */
1279 if (!vma_can_userfault(cur))
1282 * If this vma contains ending address, and huge pages
1285 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1286 end > cur->vm_start) {
1287 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1291 if (end & (vma_hpagesize - 1))
1296 * Check that this vma isn't already owned by a
1297 * different userfaultfd. We can't allow more than one
1298 * userfaultfd to own a single vma simultaneously or we
1299 * wouldn't know which one to deliver the userfaults to.
1302 if (cur->vm_userfaultfd_ctx.ctx &&
1303 cur->vm_userfaultfd_ctx.ctx != ctx)
1307 * Note vmas containing huge pages
1309 if (is_vm_hugetlb_page(cur))
1310 basic_ioctls = true;
1316 if (vma->vm_start < start)
1323 BUG_ON(!vma_can_userfault(vma));
1324 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1325 vma->vm_userfaultfd_ctx.ctx != ctx);
1328 * Nothing to do: this vma is already registered into this
1329 * userfaultfd and with the right tracking mode too.
1331 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1332 (vma->vm_flags & vm_flags) == vm_flags)
1335 if (vma->vm_start > start)
1336 start = vma->vm_start;
1337 vma_end = min(end, vma->vm_end);
1339 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1340 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1341 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1343 ((struct vm_userfaultfd_ctx){ ctx }));
1348 if (vma->vm_start < start) {
1349 ret = split_vma(mm, vma, start, 1);
1353 if (vma->vm_end > end) {
1354 ret = split_vma(mm, vma, end, 0);
1360 * In the vma_merge() successful mprotect-like case 8:
1361 * the next vma was merged into the current one and
1362 * the current one has not been updated yet.
1364 vma->vm_flags = new_flags;
1365 vma->vm_userfaultfd_ctx.ctx = ctx;
1369 start = vma->vm_end;
1371 } while (vma && vma->vm_start < end);
1373 up_write(&mm->mmap_sem);
1377 * Now that we scanned all vmas we can already tell
1378 * userland which ioctls methods are guaranteed to
1379 * succeed on this range.
1381 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1382 UFFD_API_RANGE_IOCTLS,
1383 &user_uffdio_register->ioctls))
1390 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1393 struct mm_struct *mm = ctx->mm;
1394 struct vm_area_struct *vma, *prev, *cur;
1396 struct uffdio_range uffdio_unregister;
1397 unsigned long new_flags;
1399 unsigned long start, end, vma_end;
1400 const void __user *buf = (void __user *)arg;
1403 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1406 ret = validate_range(mm, uffdio_unregister.start,
1407 uffdio_unregister.len);
1411 start = uffdio_unregister.start;
1412 end = start + uffdio_unregister.len;
1415 if (!mmget_not_zero(mm))
1418 down_write(&mm->mmap_sem);
1419 vma = find_vma_prev(mm, start, &prev);
1423 /* check that there's at least one vma in the range */
1425 if (vma->vm_start >= end)
1429 * If the first vma contains huge pages, make sure start address
1430 * is aligned to huge page size.
1432 if (is_vm_hugetlb_page(vma)) {
1433 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1435 if (start & (vma_hpagesize - 1))
1440 * Search for not compatible vmas.
1444 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1447 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1448 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1451 * Check not compatible vmas, not strictly required
1452 * here as not compatible vmas cannot have an
1453 * userfaultfd_ctx registered on them, but this
1454 * provides for more strict behavior to notice
1455 * unregistration errors.
1457 if (!vma_can_userfault(cur))
1464 if (vma->vm_start < start)
1471 BUG_ON(!vma_can_userfault(vma));
1474 * Nothing to do: this vma is already registered into this
1475 * userfaultfd and with the right tracking mode too.
1477 if (!vma->vm_userfaultfd_ctx.ctx)
1480 if (vma->vm_start > start)
1481 start = vma->vm_start;
1482 vma_end = min(end, vma->vm_end);
1484 if (userfaultfd_missing(vma)) {
1486 * Wake any concurrent pending userfault while
1487 * we unregister, so they will not hang
1488 * permanently and it avoids userland to call
1489 * UFFDIO_WAKE explicitly.
1491 struct userfaultfd_wake_range range;
1492 range.start = start;
1493 range.len = vma_end - start;
1494 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1497 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1498 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1499 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1506 if (vma->vm_start < start) {
1507 ret = split_vma(mm, vma, start, 1);
1511 if (vma->vm_end > end) {
1512 ret = split_vma(mm, vma, end, 0);
1518 * In the vma_merge() successful mprotect-like case 8:
1519 * the next vma was merged into the current one and
1520 * the current one has not been updated yet.
1522 vma->vm_flags = new_flags;
1523 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1527 start = vma->vm_end;
1529 } while (vma && vma->vm_start < end);
1531 up_write(&mm->mmap_sem);
1538 * userfaultfd_wake may be used in combination with the
1539 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1541 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1545 struct uffdio_range uffdio_wake;
1546 struct userfaultfd_wake_range range;
1547 const void __user *buf = (void __user *)arg;
1550 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1553 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1557 range.start = uffdio_wake.start;
1558 range.len = uffdio_wake.len;
1561 * len == 0 means wake all and we don't want to wake all here,
1562 * so check it again to be sure.
1564 VM_BUG_ON(!range.len);
1566 wake_userfault(ctx, &range);
1573 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1577 struct uffdio_copy uffdio_copy;
1578 struct uffdio_copy __user *user_uffdio_copy;
1579 struct userfaultfd_wake_range range;
1581 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1584 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1585 /* don't copy "copy" last field */
1586 sizeof(uffdio_copy)-sizeof(__s64)))
1589 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1593 * double check for wraparound just in case. copy_from_user()
1594 * will later check uffdio_copy.src + uffdio_copy.len to fit
1595 * in the userland range.
1598 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1600 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1602 if (mmget_not_zero(ctx->mm)) {
1603 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1609 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1614 /* len == 0 would wake all */
1616 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1617 range.start = uffdio_copy.dst;
1618 wake_userfault(ctx, &range);
1620 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1625 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1629 struct uffdio_zeropage uffdio_zeropage;
1630 struct uffdio_zeropage __user *user_uffdio_zeropage;
1631 struct userfaultfd_wake_range range;
1633 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1636 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1637 /* don't copy "zeropage" last field */
1638 sizeof(uffdio_zeropage)-sizeof(__s64)))
1641 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1642 uffdio_zeropage.range.len);
1646 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1649 if (mmget_not_zero(ctx->mm)) {
1650 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1651 uffdio_zeropage.range.len);
1656 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1660 /* len == 0 would wake all */
1663 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1664 range.start = uffdio_zeropage.range.start;
1665 wake_userfault(ctx, &range);
1667 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1672 static inline unsigned int uffd_ctx_features(__u64 user_features)
1675 * For the current set of features the bits just coincide
1677 return (unsigned int)user_features;
1681 * userland asks for a certain API version and we return which bits
1682 * and ioctl commands are implemented in this kernel for such API
1683 * version or -EINVAL if unknown.
1685 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1688 struct uffdio_api uffdio_api;
1689 void __user *buf = (void __user *)arg;
1694 if (ctx->state != UFFD_STATE_WAIT_API)
1697 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1699 features = uffdio_api.features;
1700 if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
1701 memset(&uffdio_api, 0, sizeof(uffdio_api));
1702 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1707 /* report all available features and ioctls to userland */
1708 uffdio_api.features = UFFD_API_FEATURES;
1709 uffdio_api.ioctls = UFFD_API_IOCTLS;
1711 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1713 ctx->state = UFFD_STATE_RUNNING;
1714 /* only enable the requested features for this uffd context */
1715 ctx->features = uffd_ctx_features(features);
1721 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1725 struct userfaultfd_ctx *ctx = file->private_data;
1727 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1732 ret = userfaultfd_api(ctx, arg);
1734 case UFFDIO_REGISTER:
1735 ret = userfaultfd_register(ctx, arg);
1737 case UFFDIO_UNREGISTER:
1738 ret = userfaultfd_unregister(ctx, arg);
1741 ret = userfaultfd_wake(ctx, arg);
1744 ret = userfaultfd_copy(ctx, arg);
1746 case UFFDIO_ZEROPAGE:
1747 ret = userfaultfd_zeropage(ctx, arg);
1753 #ifdef CONFIG_PROC_FS
1754 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1756 struct userfaultfd_ctx *ctx = f->private_data;
1757 wait_queue_entry_t *wq;
1758 struct userfaultfd_wait_queue *uwq;
1759 unsigned long pending = 0, total = 0;
1761 spin_lock(&ctx->fault_pending_wqh.lock);
1762 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1763 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1767 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1768 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1771 spin_unlock(&ctx->fault_pending_wqh.lock);
1774 * If more protocols will be added, there will be all shown
1775 * separated by a space. Like this:
1776 * protocols: aa:... bb:...
1778 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1779 pending, total, UFFD_API, ctx->features,
1780 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1784 static const struct file_operations userfaultfd_fops = {
1785 #ifdef CONFIG_PROC_FS
1786 .show_fdinfo = userfaultfd_show_fdinfo,
1788 .release = userfaultfd_release,
1789 .poll = userfaultfd_poll,
1790 .read = userfaultfd_read,
1791 .unlocked_ioctl = userfaultfd_ioctl,
1792 .compat_ioctl = userfaultfd_ioctl,
1793 .llseek = noop_llseek,
1796 static void init_once_userfaultfd_ctx(void *mem)
1798 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1800 init_waitqueue_head(&ctx->fault_pending_wqh);
1801 init_waitqueue_head(&ctx->fault_wqh);
1802 init_waitqueue_head(&ctx->event_wqh);
1803 init_waitqueue_head(&ctx->fd_wqh);
1804 seqcount_init(&ctx->refile_seq);
1808 * userfaultfd_file_create - Creates a userfaultfd file pointer.
1809 * @flags: Flags for the userfaultfd file.
1811 * This function creates a userfaultfd file pointer, w/out installing
1812 * it into the fd table. This is useful when the userfaultfd file is
1813 * used during the initialization of data structures that require
1814 * extra setup after the userfaultfd creation. So the userfaultfd
1815 * creation is split into the file pointer creation phase, and the
1816 * file descriptor installation phase. In this way races with
1817 * userspace closing the newly installed file descriptor can be
1818 * avoided. Returns a userfaultfd file pointer, or a proper error
1821 static struct file *userfaultfd_file_create(int flags)
1824 struct userfaultfd_ctx *ctx;
1826 BUG_ON(!current->mm);
1828 /* Check the UFFD_* constants for consistency. */
1829 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1830 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1832 file = ERR_PTR(-EINVAL);
1833 if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1836 file = ERR_PTR(-ENOMEM);
1837 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1841 atomic_set(&ctx->refcount, 1);
1844 ctx->state = UFFD_STATE_WAIT_API;
1845 ctx->released = false;
1846 ctx->mm = current->mm;
1847 /* prevent the mm struct to be freed */
1850 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1851 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1854 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1860 SYSCALL_DEFINE1(userfaultfd, int, flags)
1865 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1870 file = userfaultfd_file_create(flags);
1872 error = PTR_ERR(file);
1873 goto err_put_unused_fd;
1875 fd_install(fd, file);
1885 static int __init userfaultfd_init(void)
1887 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1888 sizeof(struct userfaultfd_ctx),
1890 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1891 init_once_userfaultfd_ctx);
1894 __initcall(userfaultfd_init);