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 ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
234 pte = huge_ptep_get(ptep);
237 * Lockless access: we're in a wait_event so it's ok if it
240 if (huge_pte_none(pte))
242 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
248 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
249 struct vm_area_struct *vma,
250 unsigned long address,
252 unsigned long reason)
254 return false; /* should never get here */
256 #endif /* CONFIG_HUGETLB_PAGE */
259 * Verify the pagetables are still not ok after having reigstered into
260 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
261 * userfault that has already been resolved, if userfaultfd_read and
262 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
265 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
266 unsigned long address,
268 unsigned long reason)
270 struct mm_struct *mm = ctx->mm;
278 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
280 pgd = pgd_offset(mm, address);
281 if (!pgd_present(*pgd))
283 p4d = p4d_offset(pgd, address);
284 if (!p4d_present(*p4d))
286 pud = pud_offset(p4d, address);
287 if (!pud_present(*pud))
289 pmd = pmd_offset(pud, address);
291 * READ_ONCE must function as a barrier with narrower scope
292 * and it must be equivalent to:
293 * _pmd = *pmd; barrier();
295 * This is to deal with the instability (as in
296 * pmd_trans_unstable) of the pmd.
298 _pmd = READ_ONCE(*pmd);
299 if (!pmd_present(_pmd))
303 if (pmd_trans_huge(_pmd))
307 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
308 * and use the standard pte_offset_map() instead of parsing _pmd.
310 pte = pte_offset_map(pmd, address);
312 * Lockless access: we're in a wait_event so it's ok if it
324 * The locking rules involved in returning VM_FAULT_RETRY depending on
325 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
326 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
327 * recommendation in __lock_page_or_retry is not an understatement.
329 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
330 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
333 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
334 * set, VM_FAULT_RETRY can still be returned if and only if there are
335 * fatal_signal_pending()s, and the mmap_sem must be released before
338 int handle_userfault(struct vm_fault *vmf, unsigned long reason)
340 struct mm_struct *mm = vmf->vma->vm_mm;
341 struct userfaultfd_ctx *ctx;
342 struct userfaultfd_wait_queue uwq;
344 bool must_wait, return_to_userland;
347 ret = VM_FAULT_SIGBUS;
350 * We don't do userfault handling for the final child pid update.
352 * We also don't do userfault handling during
353 * coredumping. hugetlbfs has the special
354 * follow_hugetlb_page() to skip missing pages in the
355 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
356 * the no_page_table() helper in follow_page_mask(), but the
357 * shmem_vm_ops->fault method is invoked even during
358 * coredumping without mmap_sem and it ends up here.
360 if (current->flags & (PF_EXITING|PF_DUMPCORE))
364 * Coredumping runs without mmap_sem so we can only check that
365 * the mmap_sem is held, if PF_DUMPCORE was not set.
367 WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
369 ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
373 BUG_ON(ctx->mm != mm);
375 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
376 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
378 if (ctx->features & UFFD_FEATURE_SIGBUS)
382 * If it's already released don't get it. This avoids to loop
383 * in __get_user_pages if userfaultfd_release waits on the
384 * caller of handle_userfault to release the mmap_sem.
386 if (unlikely(ACCESS_ONCE(ctx->released))) {
388 * Don't return VM_FAULT_SIGBUS in this case, so a non
389 * cooperative manager can close the uffd after the
390 * last UFFDIO_COPY, without risking to trigger an
391 * involuntary SIGBUS if the process was starting the
392 * userfaultfd while the userfaultfd was still armed
393 * (but after the last UFFDIO_COPY). If the uffd
394 * wasn't already closed when the userfault reached
395 * this point, that would normally be solved by
396 * userfaultfd_must_wait returning 'false'.
398 * If we were to return VM_FAULT_SIGBUS here, the non
399 * cooperative manager would be instead forced to
400 * always call UFFDIO_UNREGISTER before it can safely
403 ret = VM_FAULT_NOPAGE;
408 * Check that we can return VM_FAULT_RETRY.
410 * NOTE: it should become possible to return VM_FAULT_RETRY
411 * even if FAULT_FLAG_TRIED is set without leading to gup()
412 * -EBUSY failures, if the userfaultfd is to be extended for
413 * VM_UFFD_WP tracking and we intend to arm the userfault
414 * without first stopping userland access to the memory. For
415 * VM_UFFD_MISSING userfaults this is enough for now.
417 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
419 * Validate the invariant that nowait must allow retry
420 * to be sure not to return SIGBUS erroneously on
421 * nowait invocations.
423 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
424 #ifdef CONFIG_DEBUG_VM
425 if (printk_ratelimit()) {
427 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
436 * Handle nowait, not much to do other than tell it to retry
439 ret = VM_FAULT_RETRY;
440 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
443 /* take the reference before dropping the mmap_sem */
444 userfaultfd_ctx_get(ctx);
446 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
447 uwq.wq.private = current;
448 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
454 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
455 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
456 blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
459 spin_lock(&ctx->fault_pending_wqh.lock);
461 * After the __add_wait_queue the uwq is visible to userland
462 * through poll/read().
464 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
466 * The smp_mb() after __set_current_state prevents the reads
467 * following the spin_unlock to happen before the list_add in
470 set_current_state(blocking_state);
471 spin_unlock(&ctx->fault_pending_wqh.lock);
473 if (!is_vm_hugetlb_page(vmf->vma))
474 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
477 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
480 up_read(&mm->mmap_sem);
482 if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
483 (return_to_userland ? !signal_pending(current) :
484 !fatal_signal_pending(current)))) {
485 wake_up_poll(&ctx->fd_wqh, POLLIN);
487 ret |= VM_FAULT_MAJOR;
490 * False wakeups can orginate even from rwsem before
491 * up_read() however userfaults will wait either for a
492 * targeted wakeup on the specific uwq waitqueue from
493 * wake_userfault() or for signals or for uffd
496 while (!READ_ONCE(uwq.waken)) {
498 * This needs the full smp_store_mb()
499 * guarantee as the state write must be
500 * visible to other CPUs before reading
501 * uwq.waken from other CPUs.
503 set_current_state(blocking_state);
504 if (READ_ONCE(uwq.waken) ||
505 READ_ONCE(ctx->released) ||
506 (return_to_userland ? signal_pending(current) :
507 fatal_signal_pending(current)))
513 __set_current_state(TASK_RUNNING);
515 if (return_to_userland) {
516 if (signal_pending(current) &&
517 !fatal_signal_pending(current)) {
519 * If we got a SIGSTOP or SIGCONT and this is
520 * a normal userland page fault, just let
521 * userland return so the signal will be
522 * handled and gdb debugging works. The page
523 * fault code immediately after we return from
524 * this function is going to release the
525 * mmap_sem and it's not depending on it
526 * (unlike gup would if we were not to return
529 * If a fatal signal is pending we still take
530 * the streamlined VM_FAULT_RETRY failure path
531 * and there's no need to retake the mmap_sem
534 down_read(&mm->mmap_sem);
535 ret = VM_FAULT_NOPAGE;
540 * Here we race with the list_del; list_add in
541 * userfaultfd_ctx_read(), however because we don't ever run
542 * list_del_init() to refile across the two lists, the prev
543 * and next pointers will never point to self. list_add also
544 * would never let any of the two pointers to point to
545 * self. So list_empty_careful won't risk to see both pointers
546 * pointing to self at any time during the list refile. The
547 * only case where list_del_init() is called is the full
548 * removal in the wake function and there we don't re-list_add
549 * and it's fine not to block on the spinlock. The uwq on this
550 * kernel stack can be released after the list_del_init.
552 if (!list_empty_careful(&uwq.wq.entry)) {
553 spin_lock(&ctx->fault_pending_wqh.lock);
555 * No need of list_del_init(), the uwq on the stack
556 * will be freed shortly anyway.
558 list_del(&uwq.wq.entry);
559 spin_unlock(&ctx->fault_pending_wqh.lock);
563 * ctx may go away after this if the userfault pseudo fd is
566 userfaultfd_ctx_put(ctx);
572 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
573 struct userfaultfd_wait_queue *ewq)
575 struct userfaultfd_ctx *release_new_ctx;
577 if (WARN_ON_ONCE(current->flags & PF_EXITING))
581 init_waitqueue_entry(&ewq->wq, current);
582 release_new_ctx = NULL;
584 spin_lock(&ctx->event_wqh.lock);
586 * After the __add_wait_queue the uwq is visible to userland
587 * through poll/read().
589 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
591 set_current_state(TASK_KILLABLE);
592 if (ewq->msg.event == 0)
594 if (ACCESS_ONCE(ctx->released) ||
595 fatal_signal_pending(current)) {
597 * &ewq->wq may be queued in fork_event, but
598 * __remove_wait_queue ignores the head
599 * parameter. It would be a problem if it
602 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
603 if (ewq->msg.event == UFFD_EVENT_FORK) {
604 struct userfaultfd_ctx *new;
606 new = (struct userfaultfd_ctx *)
608 ewq->msg.arg.reserved.reserved1;
609 release_new_ctx = new;
614 spin_unlock(&ctx->event_wqh.lock);
616 wake_up_poll(&ctx->fd_wqh, POLLIN);
619 spin_lock(&ctx->event_wqh.lock);
621 __set_current_state(TASK_RUNNING);
622 spin_unlock(&ctx->event_wqh.lock);
624 if (release_new_ctx) {
625 struct vm_area_struct *vma;
626 struct mm_struct *mm = release_new_ctx->mm;
628 /* the various vma->vm_userfaultfd_ctx still points to it */
629 down_write(&mm->mmap_sem);
630 /* no task can run (and in turn coredump) yet */
631 VM_WARN_ON(!mmget_still_valid(mm));
632 for (vma = mm->mmap; vma; vma = vma->vm_next)
633 if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
634 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
635 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
637 up_write(&mm->mmap_sem);
639 userfaultfd_ctx_put(release_new_ctx);
643 * ctx may go away after this if the userfault pseudo fd is
647 userfaultfd_ctx_put(ctx);
650 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
651 struct userfaultfd_wait_queue *ewq)
654 wake_up_locked(&ctx->event_wqh);
655 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
658 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
660 struct userfaultfd_ctx *ctx = NULL, *octx;
661 struct userfaultfd_fork_ctx *fctx;
663 octx = vma->vm_userfaultfd_ctx.ctx;
664 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
665 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
666 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
670 list_for_each_entry(fctx, fcs, list)
671 if (fctx->orig == octx) {
677 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
681 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
687 atomic_set(&ctx->refcount, 1);
688 ctx->flags = octx->flags;
689 ctx->state = UFFD_STATE_RUNNING;
690 ctx->features = octx->features;
691 ctx->released = false;
692 ctx->mm = vma->vm_mm;
693 atomic_inc(&ctx->mm->mm_count);
695 userfaultfd_ctx_get(octx);
698 list_add_tail(&fctx->list, fcs);
701 vma->vm_userfaultfd_ctx.ctx = ctx;
705 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
707 struct userfaultfd_ctx *ctx = fctx->orig;
708 struct userfaultfd_wait_queue ewq;
712 ewq.msg.event = UFFD_EVENT_FORK;
713 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
715 userfaultfd_event_wait_completion(ctx, &ewq);
718 void dup_userfaultfd_complete(struct list_head *fcs)
720 struct userfaultfd_fork_ctx *fctx, *n;
722 list_for_each_entry_safe(fctx, n, fcs, list) {
724 list_del(&fctx->list);
729 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
730 struct vm_userfaultfd_ctx *vm_ctx)
732 struct userfaultfd_ctx *ctx;
734 ctx = vma->vm_userfaultfd_ctx.ctx;
735 if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
737 userfaultfd_ctx_get(ctx);
741 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
742 unsigned long from, unsigned long to,
745 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
746 struct userfaultfd_wait_queue ewq;
751 if (to & ~PAGE_MASK) {
752 userfaultfd_ctx_put(ctx);
758 ewq.msg.event = UFFD_EVENT_REMAP;
759 ewq.msg.arg.remap.from = from;
760 ewq.msg.arg.remap.to = to;
761 ewq.msg.arg.remap.len = len;
763 userfaultfd_event_wait_completion(ctx, &ewq);
766 bool userfaultfd_remove(struct vm_area_struct *vma,
767 unsigned long start, unsigned long end)
769 struct mm_struct *mm = vma->vm_mm;
770 struct userfaultfd_ctx *ctx;
771 struct userfaultfd_wait_queue ewq;
773 ctx = vma->vm_userfaultfd_ctx.ctx;
774 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
777 userfaultfd_ctx_get(ctx);
778 up_read(&mm->mmap_sem);
782 ewq.msg.event = UFFD_EVENT_REMOVE;
783 ewq.msg.arg.remove.start = start;
784 ewq.msg.arg.remove.end = end;
786 userfaultfd_event_wait_completion(ctx, &ewq);
791 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
792 unsigned long start, unsigned long end)
794 struct userfaultfd_unmap_ctx *unmap_ctx;
796 list_for_each_entry(unmap_ctx, unmaps, list)
797 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
798 unmap_ctx->end == end)
804 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
805 unsigned long start, unsigned long end,
806 struct list_head *unmaps)
808 for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
809 struct userfaultfd_unmap_ctx *unmap_ctx;
810 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
812 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
813 has_unmap_ctx(ctx, unmaps, start, end))
816 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
820 userfaultfd_ctx_get(ctx);
821 unmap_ctx->ctx = ctx;
822 unmap_ctx->start = start;
823 unmap_ctx->end = end;
824 list_add_tail(&unmap_ctx->list, unmaps);
830 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
832 struct userfaultfd_unmap_ctx *ctx, *n;
833 struct userfaultfd_wait_queue ewq;
835 list_for_each_entry_safe(ctx, n, uf, list) {
838 ewq.msg.event = UFFD_EVENT_UNMAP;
839 ewq.msg.arg.remove.start = ctx->start;
840 ewq.msg.arg.remove.end = ctx->end;
842 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
844 list_del(&ctx->list);
849 static int userfaultfd_release(struct inode *inode, struct file *file)
851 struct userfaultfd_ctx *ctx = file->private_data;
852 struct mm_struct *mm = ctx->mm;
853 struct vm_area_struct *vma, *prev;
854 /* len == 0 means wake all */
855 struct userfaultfd_wake_range range = { .len = 0, };
856 unsigned long new_flags;
859 ACCESS_ONCE(ctx->released) = true;
861 if (!mmget_not_zero(mm))
865 * Flush page faults out of all CPUs. NOTE: all page faults
866 * must be retried without returning VM_FAULT_SIGBUS if
867 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
868 * changes while handle_userfault released the mmap_sem. So
869 * it's critical that released is set to true (above), before
870 * taking the mmap_sem for writing.
872 down_write(&mm->mmap_sem);
873 still_valid = mmget_still_valid(mm);
875 for (vma = mm->mmap; vma; vma = vma->vm_next) {
877 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
878 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
879 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
883 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
885 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
886 new_flags, vma->anon_vma,
887 vma->vm_file, vma->vm_pgoff,
895 vma->vm_flags = new_flags;
896 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
898 up_write(&mm->mmap_sem);
902 * After no new page faults can wait on this fault_*wqh, flush
903 * the last page faults that may have been already waiting on
906 spin_lock(&ctx->fault_pending_wqh.lock);
907 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
908 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
909 spin_unlock(&ctx->fault_pending_wqh.lock);
911 /* Flush pending events that may still wait on event_wqh */
912 wake_up_all(&ctx->event_wqh);
914 wake_up_poll(&ctx->fd_wqh, POLLHUP);
915 userfaultfd_ctx_put(ctx);
919 /* fault_pending_wqh.lock must be hold by the caller */
920 static inline struct userfaultfd_wait_queue *find_userfault_in(
921 wait_queue_head_t *wqh)
923 wait_queue_entry_t *wq;
924 struct userfaultfd_wait_queue *uwq;
926 VM_BUG_ON(!spin_is_locked(&wqh->lock));
929 if (!waitqueue_active(wqh))
931 /* walk in reverse to provide FIFO behavior to read userfaults */
932 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
933 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
938 static inline struct userfaultfd_wait_queue *find_userfault(
939 struct userfaultfd_ctx *ctx)
941 return find_userfault_in(&ctx->fault_pending_wqh);
944 static inline struct userfaultfd_wait_queue *find_userfault_evt(
945 struct userfaultfd_ctx *ctx)
947 return find_userfault_in(&ctx->event_wqh);
950 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
952 struct userfaultfd_ctx *ctx = file->private_data;
955 poll_wait(file, &ctx->fd_wqh, wait);
957 switch (ctx->state) {
958 case UFFD_STATE_WAIT_API:
960 case UFFD_STATE_RUNNING:
962 * poll() never guarantees that read won't block.
963 * userfaults can be waken before they're read().
965 if (unlikely(!(file->f_flags & O_NONBLOCK)))
968 * lockless access to see if there are pending faults
969 * __pollwait last action is the add_wait_queue but
970 * the spin_unlock would allow the waitqueue_active to
971 * pass above the actual list_add inside
972 * add_wait_queue critical section. So use a full
973 * memory barrier to serialize the list_add write of
974 * add_wait_queue() with the waitqueue_active read
979 if (waitqueue_active(&ctx->fault_pending_wqh))
981 else if (waitqueue_active(&ctx->event_wqh))
991 static const struct file_operations userfaultfd_fops;
993 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
994 struct userfaultfd_ctx *new,
995 struct uffd_msg *msg)
999 unsigned int flags = new->flags & UFFD_SHARED_FCNTL_FLAGS;
1001 fd = get_unused_fd_flags(flags);
1005 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, new,
1009 return PTR_ERR(file);
1012 fd_install(fd, file);
1013 msg->arg.reserved.reserved1 = 0;
1014 msg->arg.fork.ufd = fd;
1019 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1020 struct uffd_msg *msg)
1023 DECLARE_WAITQUEUE(wait, current);
1024 struct userfaultfd_wait_queue *uwq;
1026 * Handling fork event requires sleeping operations, so
1027 * we drop the event_wqh lock, then do these ops, then
1028 * lock it back and wake up the waiter. While the lock is
1029 * dropped the ewq may go away so we keep track of it
1032 LIST_HEAD(fork_event);
1033 struct userfaultfd_ctx *fork_nctx = NULL;
1035 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1036 spin_lock(&ctx->fd_wqh.lock);
1037 __add_wait_queue(&ctx->fd_wqh, &wait);
1039 set_current_state(TASK_INTERRUPTIBLE);
1040 spin_lock(&ctx->fault_pending_wqh.lock);
1041 uwq = find_userfault(ctx);
1044 * Use a seqcount to repeat the lockless check
1045 * in wake_userfault() to avoid missing
1046 * wakeups because during the refile both
1047 * waitqueue could become empty if this is the
1050 write_seqcount_begin(&ctx->refile_seq);
1053 * The fault_pending_wqh.lock prevents the uwq
1054 * to disappear from under us.
1056 * Refile this userfault from
1057 * fault_pending_wqh to fault_wqh, it's not
1058 * pending anymore after we read it.
1060 * Use list_del() by hand (as
1061 * userfaultfd_wake_function also uses
1062 * list_del_init() by hand) to be sure nobody
1063 * changes __remove_wait_queue() to use
1064 * list_del_init() in turn breaking the
1065 * !list_empty_careful() check in
1066 * handle_userfault(). The uwq->wq.head list
1067 * must never be empty at any time during the
1068 * refile, or the waitqueue could disappear
1069 * from under us. The "wait_queue_head_t"
1070 * parameter of __remove_wait_queue() is unused
1073 list_del(&uwq->wq.entry);
1074 __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1076 write_seqcount_end(&ctx->refile_seq);
1078 /* careful to always initialize msg if ret == 0 */
1080 spin_unlock(&ctx->fault_pending_wqh.lock);
1084 spin_unlock(&ctx->fault_pending_wqh.lock);
1086 spin_lock(&ctx->event_wqh.lock);
1087 uwq = find_userfault_evt(ctx);
1091 if (uwq->msg.event == UFFD_EVENT_FORK) {
1092 fork_nctx = (struct userfaultfd_ctx *)
1094 uwq->msg.arg.reserved.reserved1;
1095 list_move(&uwq->wq.entry, &fork_event);
1097 * fork_nctx can be freed as soon as
1098 * we drop the lock, unless we take a
1101 userfaultfd_ctx_get(fork_nctx);
1102 spin_unlock(&ctx->event_wqh.lock);
1107 userfaultfd_event_complete(ctx, uwq);
1108 spin_unlock(&ctx->event_wqh.lock);
1112 spin_unlock(&ctx->event_wqh.lock);
1114 if (signal_pending(current)) {
1122 spin_unlock(&ctx->fd_wqh.lock);
1124 spin_lock(&ctx->fd_wqh.lock);
1126 __remove_wait_queue(&ctx->fd_wqh, &wait);
1127 __set_current_state(TASK_RUNNING);
1128 spin_unlock(&ctx->fd_wqh.lock);
1130 if (!ret && msg->event == UFFD_EVENT_FORK) {
1131 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1132 spin_lock(&ctx->event_wqh.lock);
1133 if (!list_empty(&fork_event)) {
1135 * The fork thread didn't abort, so we can
1136 * drop the temporary refcount.
1138 userfaultfd_ctx_put(fork_nctx);
1140 uwq = list_first_entry(&fork_event,
1144 * If fork_event list wasn't empty and in turn
1145 * the event wasn't already released by fork
1146 * (the event is allocated on fork kernel
1147 * stack), put the event back to its place in
1148 * the event_wq. fork_event head will be freed
1149 * as soon as we return so the event cannot
1150 * stay queued there no matter the current
1153 list_del(&uwq->wq.entry);
1154 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1157 * Leave the event in the waitqueue and report
1158 * error to userland if we failed to resolve
1159 * the userfault fork.
1162 userfaultfd_event_complete(ctx, uwq);
1165 * Here the fork thread aborted and the
1166 * refcount from the fork thread on fork_nctx
1167 * has already been released. We still hold
1168 * the reference we took before releasing the
1169 * lock above. If resolve_userfault_fork
1170 * failed we've to drop it because the
1171 * fork_nctx has to be freed in such case. If
1172 * it succeeded we'll hold it because the new
1173 * uffd references it.
1176 userfaultfd_ctx_put(fork_nctx);
1178 spin_unlock(&ctx->event_wqh.lock);
1184 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1185 size_t count, loff_t *ppos)
1187 struct userfaultfd_ctx *ctx = file->private_data;
1188 ssize_t _ret, ret = 0;
1189 struct uffd_msg msg;
1190 int no_wait = file->f_flags & O_NONBLOCK;
1192 if (ctx->state == UFFD_STATE_WAIT_API)
1196 if (count < sizeof(msg))
1197 return ret ? ret : -EINVAL;
1198 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1200 return ret ? ret : _ret;
1201 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1202 return ret ? ret : -EFAULT;
1205 count -= sizeof(msg);
1207 * Allow to read more than one fault at time but only
1208 * block if waiting for the very first one.
1210 no_wait = O_NONBLOCK;
1214 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1215 struct userfaultfd_wake_range *range)
1217 spin_lock(&ctx->fault_pending_wqh.lock);
1218 /* wake all in the range and autoremove */
1219 if (waitqueue_active(&ctx->fault_pending_wqh))
1220 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1222 if (waitqueue_active(&ctx->fault_wqh))
1223 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
1224 spin_unlock(&ctx->fault_pending_wqh.lock);
1227 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1228 struct userfaultfd_wake_range *range)
1234 * To be sure waitqueue_active() is not reordered by the CPU
1235 * before the pagetable update, use an explicit SMP memory
1236 * barrier here. PT lock release or up_read(mmap_sem) still
1237 * have release semantics that can allow the
1238 * waitqueue_active() to be reordered before the pte update.
1243 * Use waitqueue_active because it's very frequent to
1244 * change the address space atomically even if there are no
1245 * userfaults yet. So we take the spinlock only when we're
1246 * sure we've userfaults to wake.
1249 seq = read_seqcount_begin(&ctx->refile_seq);
1250 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1251 waitqueue_active(&ctx->fault_wqh);
1253 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1255 __wake_userfault(ctx, range);
1258 static __always_inline int validate_range(struct mm_struct *mm,
1259 __u64 start, __u64 len)
1261 __u64 task_size = mm->task_size;
1263 if (start & ~PAGE_MASK)
1265 if (len & ~PAGE_MASK)
1269 if (start < mmap_min_addr)
1271 if (start >= task_size)
1273 if (len > task_size - start)
1278 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1280 return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1284 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1287 struct mm_struct *mm = ctx->mm;
1288 struct vm_area_struct *vma, *prev, *cur;
1290 struct uffdio_register uffdio_register;
1291 struct uffdio_register __user *user_uffdio_register;
1292 unsigned long vm_flags, new_flags;
1295 unsigned long start, end, vma_end;
1297 user_uffdio_register = (struct uffdio_register __user *) arg;
1300 if (copy_from_user(&uffdio_register, user_uffdio_register,
1301 sizeof(uffdio_register)-sizeof(__u64)))
1305 if (!uffdio_register.mode)
1307 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1308 UFFDIO_REGISTER_MODE_WP))
1311 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1312 vm_flags |= VM_UFFD_MISSING;
1313 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1314 vm_flags |= VM_UFFD_WP;
1316 * FIXME: remove the below error constraint by
1317 * implementing the wprotect tracking mode.
1323 ret = validate_range(mm, uffdio_register.range.start,
1324 uffdio_register.range.len);
1328 start = uffdio_register.range.start;
1329 end = start + uffdio_register.range.len;
1332 if (!mmget_not_zero(mm))
1335 down_write(&mm->mmap_sem);
1336 if (!mmget_still_valid(mm))
1338 vma = find_vma_prev(mm, start, &prev);
1342 /* check that there's at least one vma in the range */
1344 if (vma->vm_start >= end)
1348 * If the first vma contains huge pages, make sure start address
1349 * is aligned to huge page size.
1351 if (is_vm_hugetlb_page(vma)) {
1352 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1354 if (start & (vma_hpagesize - 1))
1359 * Search for not compatible vmas.
1362 basic_ioctls = false;
1363 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1366 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1367 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1369 /* check not compatible vmas */
1371 if (!vma_can_userfault(cur))
1375 * UFFDIO_COPY will fill file holes even without
1376 * PROT_WRITE. This check enforces that if this is a
1377 * MAP_SHARED, the process has write permission to the backing
1378 * file. If VM_MAYWRITE is set it also enforces that on a
1379 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1380 * F_WRITE_SEAL can be taken until the vma is destroyed.
1383 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1387 * If this vma contains ending address, and huge pages
1390 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1391 end > cur->vm_start) {
1392 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1396 if (end & (vma_hpagesize - 1))
1401 * Check that this vma isn't already owned by a
1402 * different userfaultfd. We can't allow more than one
1403 * userfaultfd to own a single vma simultaneously or we
1404 * wouldn't know which one to deliver the userfaults to.
1407 if (cur->vm_userfaultfd_ctx.ctx &&
1408 cur->vm_userfaultfd_ctx.ctx != ctx)
1412 * Note vmas containing huge pages
1414 if (is_vm_hugetlb_page(cur))
1415 basic_ioctls = true;
1421 if (vma->vm_start < start)
1428 BUG_ON(!vma_can_userfault(vma));
1429 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1430 vma->vm_userfaultfd_ctx.ctx != ctx);
1431 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1434 * Nothing to do: this vma is already registered into this
1435 * userfaultfd and with the right tracking mode too.
1437 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1438 (vma->vm_flags & vm_flags) == vm_flags)
1441 if (vma->vm_start > start)
1442 start = vma->vm_start;
1443 vma_end = min(end, vma->vm_end);
1445 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1446 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1447 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1449 ((struct vm_userfaultfd_ctx){ ctx }));
1454 if (vma->vm_start < start) {
1455 ret = split_vma(mm, vma, start, 1);
1459 if (vma->vm_end > end) {
1460 ret = split_vma(mm, vma, end, 0);
1466 * In the vma_merge() successful mprotect-like case 8:
1467 * the next vma was merged into the current one and
1468 * the current one has not been updated yet.
1470 vma->vm_flags = new_flags;
1471 vma->vm_userfaultfd_ctx.ctx = ctx;
1475 start = vma->vm_end;
1477 } while (vma && vma->vm_start < end);
1479 up_write(&mm->mmap_sem);
1483 * Now that we scanned all vmas we can already tell
1484 * userland which ioctls methods are guaranteed to
1485 * succeed on this range.
1487 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1488 UFFD_API_RANGE_IOCTLS,
1489 &user_uffdio_register->ioctls))
1496 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1499 struct mm_struct *mm = ctx->mm;
1500 struct vm_area_struct *vma, *prev, *cur;
1502 struct uffdio_range uffdio_unregister;
1503 unsigned long new_flags;
1505 unsigned long start, end, vma_end;
1506 const void __user *buf = (void __user *)arg;
1509 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1512 ret = validate_range(mm, uffdio_unregister.start,
1513 uffdio_unregister.len);
1517 start = uffdio_unregister.start;
1518 end = start + uffdio_unregister.len;
1521 if (!mmget_not_zero(mm))
1524 down_write(&mm->mmap_sem);
1525 if (!mmget_still_valid(mm))
1527 vma = find_vma_prev(mm, start, &prev);
1531 /* check that there's at least one vma in the range */
1533 if (vma->vm_start >= end)
1537 * If the first vma contains huge pages, make sure start address
1538 * is aligned to huge page size.
1540 if (is_vm_hugetlb_page(vma)) {
1541 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1543 if (start & (vma_hpagesize - 1))
1548 * Search for not compatible vmas.
1552 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1555 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1556 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1559 * Check not compatible vmas, not strictly required
1560 * here as not compatible vmas cannot have an
1561 * userfaultfd_ctx registered on them, but this
1562 * provides for more strict behavior to notice
1563 * unregistration errors.
1565 if (!vma_can_userfault(cur))
1572 if (vma->vm_start < start)
1579 BUG_ON(!vma_can_userfault(vma));
1582 * Nothing to do: this vma is already registered into this
1583 * userfaultfd and with the right tracking mode too.
1585 if (!vma->vm_userfaultfd_ctx.ctx)
1588 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1590 if (vma->vm_start > start)
1591 start = vma->vm_start;
1592 vma_end = min(end, vma->vm_end);
1594 if (userfaultfd_missing(vma)) {
1596 * Wake any concurrent pending userfault while
1597 * we unregister, so they will not hang
1598 * permanently and it avoids userland to call
1599 * UFFDIO_WAKE explicitly.
1601 struct userfaultfd_wake_range range;
1602 range.start = start;
1603 range.len = vma_end - start;
1604 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1607 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1608 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1609 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1616 if (vma->vm_start < start) {
1617 ret = split_vma(mm, vma, start, 1);
1621 if (vma->vm_end > end) {
1622 ret = split_vma(mm, vma, end, 0);
1628 * In the vma_merge() successful mprotect-like case 8:
1629 * the next vma was merged into the current one and
1630 * the current one has not been updated yet.
1632 vma->vm_flags = new_flags;
1633 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1637 start = vma->vm_end;
1639 } while (vma && vma->vm_start < end);
1641 up_write(&mm->mmap_sem);
1648 * userfaultfd_wake may be used in combination with the
1649 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1651 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1655 struct uffdio_range uffdio_wake;
1656 struct userfaultfd_wake_range range;
1657 const void __user *buf = (void __user *)arg;
1660 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1663 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1667 range.start = uffdio_wake.start;
1668 range.len = uffdio_wake.len;
1671 * len == 0 means wake all and we don't want to wake all here,
1672 * so check it again to be sure.
1674 VM_BUG_ON(!range.len);
1676 wake_userfault(ctx, &range);
1683 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1687 struct uffdio_copy uffdio_copy;
1688 struct uffdio_copy __user *user_uffdio_copy;
1689 struct userfaultfd_wake_range range;
1691 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1694 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1695 /* don't copy "copy" last field */
1696 sizeof(uffdio_copy)-sizeof(__s64)))
1699 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1703 * double check for wraparound just in case. copy_from_user()
1704 * will later check uffdio_copy.src + uffdio_copy.len to fit
1705 * in the userland range.
1708 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1710 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1712 if (mmget_not_zero(ctx->mm)) {
1713 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1719 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1724 /* len == 0 would wake all */
1726 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1727 range.start = uffdio_copy.dst;
1728 wake_userfault(ctx, &range);
1730 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1735 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1739 struct uffdio_zeropage uffdio_zeropage;
1740 struct uffdio_zeropage __user *user_uffdio_zeropage;
1741 struct userfaultfd_wake_range range;
1743 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1746 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1747 /* don't copy "zeropage" last field */
1748 sizeof(uffdio_zeropage)-sizeof(__s64)))
1751 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1752 uffdio_zeropage.range.len);
1756 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1759 if (mmget_not_zero(ctx->mm)) {
1760 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1761 uffdio_zeropage.range.len);
1766 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1770 /* len == 0 would wake all */
1773 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1774 range.start = uffdio_zeropage.range.start;
1775 wake_userfault(ctx, &range);
1777 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1782 static inline unsigned int uffd_ctx_features(__u64 user_features)
1785 * For the current set of features the bits just coincide
1787 return (unsigned int)user_features;
1791 * userland asks for a certain API version and we return which bits
1792 * and ioctl commands are implemented in this kernel for such API
1793 * version or -EINVAL if unknown.
1795 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1798 struct uffdio_api uffdio_api;
1799 void __user *buf = (void __user *)arg;
1804 if (ctx->state != UFFD_STATE_WAIT_API)
1807 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1809 features = uffdio_api.features;
1811 if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
1814 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
1816 /* report all available features and ioctls to userland */
1817 uffdio_api.features = UFFD_API_FEATURES;
1818 uffdio_api.ioctls = UFFD_API_IOCTLS;
1820 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1822 ctx->state = UFFD_STATE_RUNNING;
1823 /* only enable the requested features for this uffd context */
1824 ctx->features = uffd_ctx_features(features);
1829 memset(&uffdio_api, 0, sizeof(uffdio_api));
1830 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1835 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1839 struct userfaultfd_ctx *ctx = file->private_data;
1841 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1846 ret = userfaultfd_api(ctx, arg);
1848 case UFFDIO_REGISTER:
1849 ret = userfaultfd_register(ctx, arg);
1851 case UFFDIO_UNREGISTER:
1852 ret = userfaultfd_unregister(ctx, arg);
1855 ret = userfaultfd_wake(ctx, arg);
1858 ret = userfaultfd_copy(ctx, arg);
1860 case UFFDIO_ZEROPAGE:
1861 ret = userfaultfd_zeropage(ctx, arg);
1867 #ifdef CONFIG_PROC_FS
1868 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1870 struct userfaultfd_ctx *ctx = f->private_data;
1871 wait_queue_entry_t *wq;
1872 struct userfaultfd_wait_queue *uwq;
1873 unsigned long pending = 0, total = 0;
1875 spin_lock(&ctx->fault_pending_wqh.lock);
1876 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1877 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1881 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1882 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1885 spin_unlock(&ctx->fault_pending_wqh.lock);
1888 * If more protocols will be added, there will be all shown
1889 * separated by a space. Like this:
1890 * protocols: aa:... bb:...
1892 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1893 pending, total, UFFD_API, ctx->features,
1894 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1898 static const struct file_operations userfaultfd_fops = {
1899 #ifdef CONFIG_PROC_FS
1900 .show_fdinfo = userfaultfd_show_fdinfo,
1902 .release = userfaultfd_release,
1903 .poll = userfaultfd_poll,
1904 .read = userfaultfd_read,
1905 .unlocked_ioctl = userfaultfd_ioctl,
1906 .compat_ioctl = userfaultfd_ioctl,
1907 .llseek = noop_llseek,
1910 static void init_once_userfaultfd_ctx(void *mem)
1912 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1914 init_waitqueue_head(&ctx->fault_pending_wqh);
1915 init_waitqueue_head(&ctx->fault_wqh);
1916 init_waitqueue_head(&ctx->event_wqh);
1917 init_waitqueue_head(&ctx->fd_wqh);
1918 seqcount_init(&ctx->refile_seq);
1922 * userfaultfd_file_create - Creates a userfaultfd file pointer.
1923 * @flags: Flags for the userfaultfd file.
1925 * This function creates a userfaultfd file pointer, w/out installing
1926 * it into the fd table. This is useful when the userfaultfd file is
1927 * used during the initialization of data structures that require
1928 * extra setup after the userfaultfd creation. So the userfaultfd
1929 * creation is split into the file pointer creation phase, and the
1930 * file descriptor installation phase. In this way races with
1931 * userspace closing the newly installed file descriptor can be
1932 * avoided. Returns a userfaultfd file pointer, or a proper error
1935 static struct file *userfaultfd_file_create(int flags)
1938 struct userfaultfd_ctx *ctx;
1940 BUG_ON(!current->mm);
1942 /* Check the UFFD_* constants for consistency. */
1943 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1944 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1946 file = ERR_PTR(-EINVAL);
1947 if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1950 file = ERR_PTR(-ENOMEM);
1951 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1955 atomic_set(&ctx->refcount, 1);
1958 ctx->state = UFFD_STATE_WAIT_API;
1959 ctx->released = false;
1960 ctx->mm = current->mm;
1961 /* prevent the mm struct to be freed */
1964 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1965 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1968 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1974 SYSCALL_DEFINE1(userfaultfd, int, flags)
1979 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1984 file = userfaultfd_file_create(flags);
1986 error = PTR_ERR(file);
1987 goto err_put_unused_fd;
1989 fd_install(fd, file);
1999 static int __init userfaultfd_init(void)
2001 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2002 sizeof(struct userfaultfd_ctx),
2004 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2005 init_once_userfaultfd_ctx);
2008 __initcall(userfaultfd_init);