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
{
85 struct userfaultfd_ctx
*ctx
;
89 struct userfaultfd_wake_range
{
94 static int userfaultfd_wake_function(wait_queue_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 implicit smp_mb__before_spinlock in try_to_wake_up()
113 * renders uwq->waken visible to other CPUs before the task is
116 ret
= wake_up_state(wq
->private, mode
);
119 * Wake only once, autoremove behavior.
121 * After the effect of list_del_init is visible to the
122 * other CPUs, the waitqueue may disappear from under
123 * us, see the !list_empty_careful() in
124 * handle_userfault(). try_to_wake_up() has an
125 * implicit smp_mb__before_spinlock, and the
126 * wq->private is read before calling the extern
127 * function "wake_up_state" (which in turns calls
128 * try_to_wake_up). While the spin_lock;spin_unlock;
129 * wouldn't be enough, the smp_mb__before_spinlock is
130 * enough to avoid an explicit smp_mb() here.
132 list_del_init(&wq
->task_list
);
138 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
140 * @ctx: [in] Pointer to the userfaultfd context.
142 static void userfaultfd_ctx_get(struct userfaultfd_ctx
*ctx
)
144 if (!atomic_inc_not_zero(&ctx
->refcount
))
149 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
151 * @ctx: [in] Pointer to userfaultfd context.
153 * The userfaultfd context reference must have been previously acquired either
154 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
156 static void userfaultfd_ctx_put(struct userfaultfd_ctx
*ctx
)
158 if (atomic_dec_and_test(&ctx
->refcount
)) {
159 VM_BUG_ON(spin_is_locked(&ctx
->fault_pending_wqh
.lock
));
160 VM_BUG_ON(waitqueue_active(&ctx
->fault_pending_wqh
));
161 VM_BUG_ON(spin_is_locked(&ctx
->fault_wqh
.lock
));
162 VM_BUG_ON(waitqueue_active(&ctx
->fault_wqh
));
163 VM_BUG_ON(spin_is_locked(&ctx
->event_wqh
.lock
));
164 VM_BUG_ON(waitqueue_active(&ctx
->event_wqh
));
165 VM_BUG_ON(spin_is_locked(&ctx
->fd_wqh
.lock
));
166 VM_BUG_ON(waitqueue_active(&ctx
->fd_wqh
));
168 kmem_cache_free(userfaultfd_ctx_cachep
, ctx
);
172 static inline void msg_init(struct uffd_msg
*msg
)
174 BUILD_BUG_ON(sizeof(struct uffd_msg
) != 32);
176 * Must use memset to zero out the paddings or kernel data is
177 * leaked to userland.
179 memset(msg
, 0, sizeof(struct uffd_msg
));
182 static inline struct uffd_msg
userfault_msg(unsigned long address
,
184 unsigned long reason
)
188 msg
.event
= UFFD_EVENT_PAGEFAULT
;
189 msg
.arg
.pagefault
.address
= address
;
190 if (flags
& FAULT_FLAG_WRITE
)
192 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
193 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
194 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
195 * was a read fault, otherwise if set it means it's
198 msg
.arg
.pagefault
.flags
|= UFFD_PAGEFAULT_FLAG_WRITE
;
199 if (reason
& VM_UFFD_WP
)
201 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
202 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
203 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
204 * a missing fault, otherwise if set it means it's a
205 * write protect fault.
207 msg
.arg
.pagefault
.flags
|= UFFD_PAGEFAULT_FLAG_WP
;
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 unsigned long address
,
219 unsigned long reason
)
221 struct mm_struct
*mm
= ctx
->mm
;
225 VM_BUG_ON(!rwsem_is_locked(&mm
->mmap_sem
));
227 pte
= huge_pte_offset(mm
, address
);
234 * Lockless access: we're in a wait_event so it's ok if it
237 if (huge_pte_none(*pte
))
239 if (!huge_pte_write(*pte
) && (reason
& VM_UFFD_WP
))
245 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx
*ctx
,
246 unsigned long address
,
248 unsigned long reason
)
250 return false; /* should never get here */
252 #endif /* CONFIG_HUGETLB_PAGE */
255 * Verify the pagetables are still not ok after having reigstered into
256 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
257 * userfault that has already been resolved, if userfaultfd_read and
258 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
261 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx
*ctx
,
262 unsigned long address
,
264 unsigned long reason
)
266 struct mm_struct
*mm
= ctx
->mm
;
274 VM_BUG_ON(!rwsem_is_locked(&mm
->mmap_sem
));
276 pgd
= pgd_offset(mm
, address
);
277 if (!pgd_present(*pgd
))
279 p4d
= p4d_offset(pgd
, address
);
280 if (!p4d_present(*p4d
))
282 pud
= pud_offset(p4d
, address
);
283 if (!pud_present(*pud
))
285 pmd
= pmd_offset(pud
, address
);
287 * READ_ONCE must function as a barrier with narrower scope
288 * and it must be equivalent to:
289 * _pmd = *pmd; barrier();
291 * This is to deal with the instability (as in
292 * pmd_trans_unstable) of the pmd.
294 _pmd
= READ_ONCE(*pmd
);
295 if (!pmd_present(_pmd
))
299 if (pmd_trans_huge(_pmd
))
303 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
304 * and use the standard pte_offset_map() instead of parsing _pmd.
306 pte
= pte_offset_map(pmd
, address
);
308 * Lockless access: we're in a wait_event so it's ok if it
320 * The locking rules involved in returning VM_FAULT_RETRY depending on
321 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
322 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
323 * recommendation in __lock_page_or_retry is not an understatement.
325 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
326 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
329 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
330 * set, VM_FAULT_RETRY can still be returned if and only if there are
331 * fatal_signal_pending()s, and the mmap_sem must be released before
334 int handle_userfault(struct vm_fault
*vmf
, unsigned long reason
)
336 struct mm_struct
*mm
= vmf
->vma
->vm_mm
;
337 struct userfaultfd_ctx
*ctx
;
338 struct userfaultfd_wait_queue uwq
;
340 bool must_wait
, return_to_userland
;
343 ret
= VM_FAULT_SIGBUS
;
346 * We don't do userfault handling for the final child pid update.
348 * We also don't do userfault handling during
349 * coredumping. hugetlbfs has the special
350 * follow_hugetlb_page() to skip missing pages in the
351 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
352 * the no_page_table() helper in follow_page_mask(), but the
353 * shmem_vm_ops->fault method is invoked even during
354 * coredumping without mmap_sem and it ends up here.
356 if (current
->flags
& (PF_EXITING
|PF_DUMPCORE
))
360 * Coredumping runs without mmap_sem so we can only check that
361 * the mmap_sem is held, if PF_DUMPCORE was not set.
363 WARN_ON_ONCE(!rwsem_is_locked(&mm
->mmap_sem
));
365 ctx
= vmf
->vma
->vm_userfaultfd_ctx
.ctx
;
369 BUG_ON(ctx
->mm
!= mm
);
371 VM_BUG_ON(reason
& ~(VM_UFFD_MISSING
|VM_UFFD_WP
));
372 VM_BUG_ON(!(reason
& VM_UFFD_MISSING
) ^ !!(reason
& VM_UFFD_WP
));
375 * If it's already released don't get it. This avoids to loop
376 * in __get_user_pages if userfaultfd_release waits on the
377 * caller of handle_userfault to release the mmap_sem.
379 if (unlikely(ACCESS_ONCE(ctx
->released
)))
383 * Check that we can return VM_FAULT_RETRY.
385 * NOTE: it should become possible to return VM_FAULT_RETRY
386 * even if FAULT_FLAG_TRIED is set without leading to gup()
387 * -EBUSY failures, if the userfaultfd is to be extended for
388 * VM_UFFD_WP tracking and we intend to arm the userfault
389 * without first stopping userland access to the memory. For
390 * VM_UFFD_MISSING userfaults this is enough for now.
392 if (unlikely(!(vmf
->flags
& FAULT_FLAG_ALLOW_RETRY
))) {
394 * Validate the invariant that nowait must allow retry
395 * to be sure not to return SIGBUS erroneously on
396 * nowait invocations.
398 BUG_ON(vmf
->flags
& FAULT_FLAG_RETRY_NOWAIT
);
399 #ifdef CONFIG_DEBUG_VM
400 if (printk_ratelimit()) {
402 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
411 * Handle nowait, not much to do other than tell it to retry
414 ret
= VM_FAULT_RETRY
;
415 if (vmf
->flags
& FAULT_FLAG_RETRY_NOWAIT
)
418 /* take the reference before dropping the mmap_sem */
419 userfaultfd_ctx_get(ctx
);
421 init_waitqueue_func_entry(&uwq
.wq
, userfaultfd_wake_function
);
422 uwq
.wq
.private = current
;
423 uwq
.msg
= userfault_msg(vmf
->address
, vmf
->flags
, reason
);
428 (vmf
->flags
& (FAULT_FLAG_USER
|FAULT_FLAG_KILLABLE
)) ==
429 (FAULT_FLAG_USER
|FAULT_FLAG_KILLABLE
);
430 blocking_state
= return_to_userland
? TASK_INTERRUPTIBLE
:
433 spin_lock(&ctx
->fault_pending_wqh
.lock
);
435 * After the __add_wait_queue the uwq is visible to userland
436 * through poll/read().
438 __add_wait_queue(&ctx
->fault_pending_wqh
, &uwq
.wq
);
440 * The smp_mb() after __set_current_state prevents the reads
441 * following the spin_unlock to happen before the list_add in
444 set_current_state(blocking_state
);
445 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
447 if (!is_vm_hugetlb_page(vmf
->vma
))
448 must_wait
= userfaultfd_must_wait(ctx
, vmf
->address
, vmf
->flags
,
451 must_wait
= userfaultfd_huge_must_wait(ctx
, vmf
->address
,
453 up_read(&mm
->mmap_sem
);
455 if (likely(must_wait
&& !ACCESS_ONCE(ctx
->released
) &&
456 (return_to_userland
? !signal_pending(current
) :
457 !fatal_signal_pending(current
)))) {
458 wake_up_poll(&ctx
->fd_wqh
, POLLIN
);
460 ret
|= VM_FAULT_MAJOR
;
463 * False wakeups can orginate even from rwsem before
464 * up_read() however userfaults will wait either for a
465 * targeted wakeup on the specific uwq waitqueue from
466 * wake_userfault() or for signals or for uffd
469 while (!READ_ONCE(uwq
.waken
)) {
471 * This needs the full smp_store_mb()
472 * guarantee as the state write must be
473 * visible to other CPUs before reading
474 * uwq.waken from other CPUs.
476 set_current_state(blocking_state
);
477 if (READ_ONCE(uwq
.waken
) ||
478 READ_ONCE(ctx
->released
) ||
479 (return_to_userland
? signal_pending(current
) :
480 fatal_signal_pending(current
)))
486 __set_current_state(TASK_RUNNING
);
488 if (return_to_userland
) {
489 if (signal_pending(current
) &&
490 !fatal_signal_pending(current
)) {
492 * If we got a SIGSTOP or SIGCONT and this is
493 * a normal userland page fault, just let
494 * userland return so the signal will be
495 * handled and gdb debugging works. The page
496 * fault code immediately after we return from
497 * this function is going to release the
498 * mmap_sem and it's not depending on it
499 * (unlike gup would if we were not to return
502 * If a fatal signal is pending we still take
503 * the streamlined VM_FAULT_RETRY failure path
504 * and there's no need to retake the mmap_sem
507 down_read(&mm
->mmap_sem
);
508 ret
= VM_FAULT_NOPAGE
;
513 * Here we race with the list_del; list_add in
514 * userfaultfd_ctx_read(), however because we don't ever run
515 * list_del_init() to refile across the two lists, the prev
516 * and next pointers will never point to self. list_add also
517 * would never let any of the two pointers to point to
518 * self. So list_empty_careful won't risk to see both pointers
519 * pointing to self at any time during the list refile. The
520 * only case where list_del_init() is called is the full
521 * removal in the wake function and there we don't re-list_add
522 * and it's fine not to block on the spinlock. The uwq on this
523 * kernel stack can be released after the list_del_init.
525 if (!list_empty_careful(&uwq
.wq
.task_list
)) {
526 spin_lock(&ctx
->fault_pending_wqh
.lock
);
528 * No need of list_del_init(), the uwq on the stack
529 * will be freed shortly anyway.
531 list_del(&uwq
.wq
.task_list
);
532 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
536 * ctx may go away after this if the userfault pseudo fd is
539 userfaultfd_ctx_put(ctx
);
545 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx
*ctx
,
546 struct userfaultfd_wait_queue
*ewq
)
548 if (WARN_ON_ONCE(current
->flags
& PF_EXITING
))
552 init_waitqueue_entry(&ewq
->wq
, current
);
554 spin_lock(&ctx
->event_wqh
.lock
);
556 * After the __add_wait_queue the uwq is visible to userland
557 * through poll/read().
559 __add_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
561 set_current_state(TASK_KILLABLE
);
562 if (ewq
->msg
.event
== 0)
564 if (ACCESS_ONCE(ctx
->released
) ||
565 fatal_signal_pending(current
)) {
566 __remove_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
567 if (ewq
->msg
.event
== UFFD_EVENT_FORK
) {
568 struct userfaultfd_ctx
*new;
570 new = (struct userfaultfd_ctx
*)
572 ewq
->msg
.arg
.reserved
.reserved1
;
574 userfaultfd_ctx_put(new);
579 spin_unlock(&ctx
->event_wqh
.lock
);
581 wake_up_poll(&ctx
->fd_wqh
, POLLIN
);
584 spin_lock(&ctx
->event_wqh
.lock
);
586 __set_current_state(TASK_RUNNING
);
587 spin_unlock(&ctx
->event_wqh
.lock
);
590 * ctx may go away after this if the userfault pseudo fd is
594 userfaultfd_ctx_put(ctx
);
597 static void userfaultfd_event_complete(struct userfaultfd_ctx
*ctx
,
598 struct userfaultfd_wait_queue
*ewq
)
601 wake_up_locked(&ctx
->event_wqh
);
602 __remove_wait_queue(&ctx
->event_wqh
, &ewq
->wq
);
605 int dup_userfaultfd(struct vm_area_struct
*vma
, struct list_head
*fcs
)
607 struct userfaultfd_ctx
*ctx
= NULL
, *octx
;
608 struct userfaultfd_fork_ctx
*fctx
;
610 octx
= vma
->vm_userfaultfd_ctx
.ctx
;
611 if (!octx
|| !(octx
->features
& UFFD_FEATURE_EVENT_FORK
)) {
612 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
613 vma
->vm_flags
&= ~(VM_UFFD_WP
| VM_UFFD_MISSING
);
617 list_for_each_entry(fctx
, fcs
, list
)
618 if (fctx
->orig
== octx
) {
624 fctx
= kmalloc(sizeof(*fctx
), GFP_KERNEL
);
628 ctx
= kmem_cache_alloc(userfaultfd_ctx_cachep
, GFP_KERNEL
);
634 atomic_set(&ctx
->refcount
, 1);
635 ctx
->flags
= octx
->flags
;
636 ctx
->state
= UFFD_STATE_RUNNING
;
637 ctx
->features
= octx
->features
;
638 ctx
->released
= false;
639 ctx
->mm
= vma
->vm_mm
;
640 atomic_inc(&ctx
->mm
->mm_count
);
642 userfaultfd_ctx_get(octx
);
645 list_add_tail(&fctx
->list
, fcs
);
648 vma
->vm_userfaultfd_ctx
.ctx
= ctx
;
652 static void dup_fctx(struct userfaultfd_fork_ctx
*fctx
)
654 struct userfaultfd_ctx
*ctx
= fctx
->orig
;
655 struct userfaultfd_wait_queue ewq
;
659 ewq
.msg
.event
= UFFD_EVENT_FORK
;
660 ewq
.msg
.arg
.reserved
.reserved1
= (unsigned long)fctx
->new;
662 userfaultfd_event_wait_completion(ctx
, &ewq
);
665 void dup_userfaultfd_complete(struct list_head
*fcs
)
667 struct userfaultfd_fork_ctx
*fctx
, *n
;
669 list_for_each_entry_safe(fctx
, n
, fcs
, list
) {
671 list_del(&fctx
->list
);
676 void mremap_userfaultfd_prep(struct vm_area_struct
*vma
,
677 struct vm_userfaultfd_ctx
*vm_ctx
)
679 struct userfaultfd_ctx
*ctx
;
681 ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
682 if (ctx
&& (ctx
->features
& UFFD_FEATURE_EVENT_REMAP
)) {
684 userfaultfd_ctx_get(ctx
);
688 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx
*vm_ctx
,
689 unsigned long from
, unsigned long to
,
692 struct userfaultfd_ctx
*ctx
= vm_ctx
->ctx
;
693 struct userfaultfd_wait_queue ewq
;
698 if (to
& ~PAGE_MASK
) {
699 userfaultfd_ctx_put(ctx
);
705 ewq
.msg
.event
= UFFD_EVENT_REMAP
;
706 ewq
.msg
.arg
.remap
.from
= from
;
707 ewq
.msg
.arg
.remap
.to
= to
;
708 ewq
.msg
.arg
.remap
.len
= len
;
710 userfaultfd_event_wait_completion(ctx
, &ewq
);
713 bool userfaultfd_remove(struct vm_area_struct
*vma
,
714 unsigned long start
, unsigned long end
)
716 struct mm_struct
*mm
= vma
->vm_mm
;
717 struct userfaultfd_ctx
*ctx
;
718 struct userfaultfd_wait_queue ewq
;
720 ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
721 if (!ctx
|| !(ctx
->features
& UFFD_FEATURE_EVENT_REMOVE
))
724 userfaultfd_ctx_get(ctx
);
725 up_read(&mm
->mmap_sem
);
729 ewq
.msg
.event
= UFFD_EVENT_REMOVE
;
730 ewq
.msg
.arg
.remove
.start
= start
;
731 ewq
.msg
.arg
.remove
.end
= end
;
733 userfaultfd_event_wait_completion(ctx
, &ewq
);
738 static bool has_unmap_ctx(struct userfaultfd_ctx
*ctx
, struct list_head
*unmaps
,
739 unsigned long start
, unsigned long end
)
741 struct userfaultfd_unmap_ctx
*unmap_ctx
;
743 list_for_each_entry(unmap_ctx
, unmaps
, list
)
744 if (unmap_ctx
->ctx
== ctx
&& unmap_ctx
->start
== start
&&
745 unmap_ctx
->end
== end
)
751 int userfaultfd_unmap_prep(struct vm_area_struct
*vma
,
752 unsigned long start
, unsigned long end
,
753 struct list_head
*unmaps
)
755 for ( ; vma
&& vma
->vm_start
< end
; vma
= vma
->vm_next
) {
756 struct userfaultfd_unmap_ctx
*unmap_ctx
;
757 struct userfaultfd_ctx
*ctx
= vma
->vm_userfaultfd_ctx
.ctx
;
759 if (!ctx
|| !(ctx
->features
& UFFD_FEATURE_EVENT_UNMAP
) ||
760 has_unmap_ctx(ctx
, unmaps
, start
, end
))
763 unmap_ctx
= kzalloc(sizeof(*unmap_ctx
), GFP_KERNEL
);
767 userfaultfd_ctx_get(ctx
);
768 unmap_ctx
->ctx
= ctx
;
769 unmap_ctx
->start
= start
;
770 unmap_ctx
->end
= end
;
771 list_add_tail(&unmap_ctx
->list
, unmaps
);
777 void userfaultfd_unmap_complete(struct mm_struct
*mm
, struct list_head
*uf
)
779 struct userfaultfd_unmap_ctx
*ctx
, *n
;
780 struct userfaultfd_wait_queue ewq
;
782 list_for_each_entry_safe(ctx
, n
, uf
, list
) {
785 ewq
.msg
.event
= UFFD_EVENT_UNMAP
;
786 ewq
.msg
.arg
.remove
.start
= ctx
->start
;
787 ewq
.msg
.arg
.remove
.end
= ctx
->end
;
789 userfaultfd_event_wait_completion(ctx
->ctx
, &ewq
);
791 list_del(&ctx
->list
);
796 static int userfaultfd_release(struct inode
*inode
, struct file
*file
)
798 struct userfaultfd_ctx
*ctx
= file
->private_data
;
799 struct mm_struct
*mm
= ctx
->mm
;
800 struct vm_area_struct
*vma
, *prev
;
801 /* len == 0 means wake all */
802 struct userfaultfd_wake_range range
= { .len
= 0, };
803 unsigned long new_flags
;
805 ACCESS_ONCE(ctx
->released
) = true;
807 if (!mmget_not_zero(mm
))
811 * Flush page faults out of all CPUs. NOTE: all page faults
812 * must be retried without returning VM_FAULT_SIGBUS if
813 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
814 * changes while handle_userfault released the mmap_sem. So
815 * it's critical that released is set to true (above), before
816 * taking the mmap_sem for writing.
818 down_write(&mm
->mmap_sem
);
820 for (vma
= mm
->mmap
; vma
; vma
= vma
->vm_next
) {
822 BUG_ON(!!vma
->vm_userfaultfd_ctx
.ctx
^
823 !!(vma
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
824 if (vma
->vm_userfaultfd_ctx
.ctx
!= ctx
) {
828 new_flags
= vma
->vm_flags
& ~(VM_UFFD_MISSING
| VM_UFFD_WP
);
829 prev
= vma_merge(mm
, prev
, vma
->vm_start
, vma
->vm_end
,
830 new_flags
, vma
->anon_vma
,
831 vma
->vm_file
, vma
->vm_pgoff
,
838 vma
->vm_flags
= new_flags
;
839 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
841 up_write(&mm
->mmap_sem
);
845 * After no new page faults can wait on this fault_*wqh, flush
846 * the last page faults that may have been already waiting on
849 spin_lock(&ctx
->fault_pending_wqh
.lock
);
850 __wake_up_locked_key(&ctx
->fault_pending_wqh
, TASK_NORMAL
, &range
);
851 __wake_up_locked_key(&ctx
->fault_wqh
, TASK_NORMAL
, &range
);
852 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
854 wake_up_poll(&ctx
->fd_wqh
, POLLHUP
);
855 userfaultfd_ctx_put(ctx
);
859 /* fault_pending_wqh.lock must be hold by the caller */
860 static inline struct userfaultfd_wait_queue
*find_userfault_in(
861 wait_queue_head_t
*wqh
)
864 struct userfaultfd_wait_queue
*uwq
;
866 VM_BUG_ON(!spin_is_locked(&wqh
->lock
));
869 if (!waitqueue_active(wqh
))
871 /* walk in reverse to provide FIFO behavior to read userfaults */
872 wq
= list_last_entry(&wqh
->task_list
, typeof(*wq
), task_list
);
873 uwq
= container_of(wq
, struct userfaultfd_wait_queue
, wq
);
878 static inline struct userfaultfd_wait_queue
*find_userfault(
879 struct userfaultfd_ctx
*ctx
)
881 return find_userfault_in(&ctx
->fault_pending_wqh
);
884 static inline struct userfaultfd_wait_queue
*find_userfault_evt(
885 struct userfaultfd_ctx
*ctx
)
887 return find_userfault_in(&ctx
->event_wqh
);
890 static unsigned int userfaultfd_poll(struct file
*file
, poll_table
*wait
)
892 struct userfaultfd_ctx
*ctx
= file
->private_data
;
895 poll_wait(file
, &ctx
->fd_wqh
, wait
);
897 switch (ctx
->state
) {
898 case UFFD_STATE_WAIT_API
:
900 case UFFD_STATE_RUNNING
:
902 * poll() never guarantees that read won't block.
903 * userfaults can be waken before they're read().
905 if (unlikely(!(file
->f_flags
& O_NONBLOCK
)))
908 * lockless access to see if there are pending faults
909 * __pollwait last action is the add_wait_queue but
910 * the spin_unlock would allow the waitqueue_active to
911 * pass above the actual list_add inside
912 * add_wait_queue critical section. So use a full
913 * memory barrier to serialize the list_add write of
914 * add_wait_queue() with the waitqueue_active read
919 if (waitqueue_active(&ctx
->fault_pending_wqh
))
921 else if (waitqueue_active(&ctx
->event_wqh
))
931 static const struct file_operations userfaultfd_fops
;
933 static int resolve_userfault_fork(struct userfaultfd_ctx
*ctx
,
934 struct userfaultfd_ctx
*new,
935 struct uffd_msg
*msg
)
939 unsigned int flags
= new->flags
& UFFD_SHARED_FCNTL_FLAGS
;
941 fd
= get_unused_fd_flags(flags
);
945 file
= anon_inode_getfile("[userfaultfd]", &userfaultfd_fops
, new,
949 return PTR_ERR(file
);
952 fd_install(fd
, file
);
953 msg
->arg
.reserved
.reserved1
= 0;
954 msg
->arg
.fork
.ufd
= fd
;
959 static ssize_t
userfaultfd_ctx_read(struct userfaultfd_ctx
*ctx
, int no_wait
,
960 struct uffd_msg
*msg
)
963 DECLARE_WAITQUEUE(wait
, current
);
964 struct userfaultfd_wait_queue
*uwq
;
966 * Handling fork event requires sleeping operations, so
967 * we drop the event_wqh lock, then do these ops, then
968 * lock it back and wake up the waiter. While the lock is
969 * dropped the ewq may go away so we keep track of it
972 LIST_HEAD(fork_event
);
973 struct userfaultfd_ctx
*fork_nctx
= NULL
;
975 /* always take the fd_wqh lock before the fault_pending_wqh lock */
976 spin_lock(&ctx
->fd_wqh
.lock
);
977 __add_wait_queue(&ctx
->fd_wqh
, &wait
);
979 set_current_state(TASK_INTERRUPTIBLE
);
980 spin_lock(&ctx
->fault_pending_wqh
.lock
);
981 uwq
= find_userfault(ctx
);
984 * Use a seqcount to repeat the lockless check
985 * in wake_userfault() to avoid missing
986 * wakeups because during the refile both
987 * waitqueue could become empty if this is the
990 write_seqcount_begin(&ctx
->refile_seq
);
993 * The fault_pending_wqh.lock prevents the uwq
994 * to disappear from under us.
996 * Refile this userfault from
997 * fault_pending_wqh to fault_wqh, it's not
998 * pending anymore after we read it.
1000 * Use list_del() by hand (as
1001 * userfaultfd_wake_function also uses
1002 * list_del_init() by hand) to be sure nobody
1003 * changes __remove_wait_queue() to use
1004 * list_del_init() in turn breaking the
1005 * !list_empty_careful() check in
1006 * handle_userfault(). The uwq->wq.task_list
1007 * must never be empty at any time during the
1008 * refile, or the waitqueue could disappear
1009 * from under us. The "wait_queue_head_t"
1010 * parameter of __remove_wait_queue() is unused
1013 list_del(&uwq
->wq
.task_list
);
1014 __add_wait_queue(&ctx
->fault_wqh
, &uwq
->wq
);
1016 write_seqcount_end(&ctx
->refile_seq
);
1018 /* careful to always initialize msg if ret == 0 */
1020 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1024 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1026 spin_lock(&ctx
->event_wqh
.lock
);
1027 uwq
= find_userfault_evt(ctx
);
1031 if (uwq
->msg
.event
== UFFD_EVENT_FORK
) {
1032 fork_nctx
= (struct userfaultfd_ctx
*)
1034 uwq
->msg
.arg
.reserved
.reserved1
;
1035 list_move(&uwq
->wq
.task_list
, &fork_event
);
1036 spin_unlock(&ctx
->event_wqh
.lock
);
1041 userfaultfd_event_complete(ctx
, uwq
);
1042 spin_unlock(&ctx
->event_wqh
.lock
);
1046 spin_unlock(&ctx
->event_wqh
.lock
);
1048 if (signal_pending(current
)) {
1056 spin_unlock(&ctx
->fd_wqh
.lock
);
1058 spin_lock(&ctx
->fd_wqh
.lock
);
1060 __remove_wait_queue(&ctx
->fd_wqh
, &wait
);
1061 __set_current_state(TASK_RUNNING
);
1062 spin_unlock(&ctx
->fd_wqh
.lock
);
1064 if (!ret
&& msg
->event
== UFFD_EVENT_FORK
) {
1065 ret
= resolve_userfault_fork(ctx
, fork_nctx
, msg
);
1068 spin_lock(&ctx
->event_wqh
.lock
);
1069 if (!list_empty(&fork_event
)) {
1070 uwq
= list_first_entry(&fork_event
,
1073 list_del(&uwq
->wq
.task_list
);
1074 __add_wait_queue(&ctx
->event_wqh
, &uwq
->wq
);
1075 userfaultfd_event_complete(ctx
, uwq
);
1077 spin_unlock(&ctx
->event_wqh
.lock
);
1084 static ssize_t
userfaultfd_read(struct file
*file
, char __user
*buf
,
1085 size_t count
, loff_t
*ppos
)
1087 struct userfaultfd_ctx
*ctx
= file
->private_data
;
1088 ssize_t _ret
, ret
= 0;
1089 struct uffd_msg msg
;
1090 int no_wait
= file
->f_flags
& O_NONBLOCK
;
1092 if (ctx
->state
== UFFD_STATE_WAIT_API
)
1096 if (count
< sizeof(msg
))
1097 return ret
? ret
: -EINVAL
;
1098 _ret
= userfaultfd_ctx_read(ctx
, no_wait
, &msg
);
1100 return ret
? ret
: _ret
;
1101 if (copy_to_user((__u64 __user
*) buf
, &msg
, sizeof(msg
)))
1102 return ret
? ret
: -EFAULT
;
1105 count
-= sizeof(msg
);
1107 * Allow to read more than one fault at time but only
1108 * block if waiting for the very first one.
1110 no_wait
= O_NONBLOCK
;
1114 static void __wake_userfault(struct userfaultfd_ctx
*ctx
,
1115 struct userfaultfd_wake_range
*range
)
1117 unsigned long start
, end
;
1119 start
= range
->start
;
1120 end
= range
->start
+ range
->len
;
1122 spin_lock(&ctx
->fault_pending_wqh
.lock
);
1123 /* wake all in the range and autoremove */
1124 if (waitqueue_active(&ctx
->fault_pending_wqh
))
1125 __wake_up_locked_key(&ctx
->fault_pending_wqh
, TASK_NORMAL
,
1127 if (waitqueue_active(&ctx
->fault_wqh
))
1128 __wake_up_locked_key(&ctx
->fault_wqh
, TASK_NORMAL
, range
);
1129 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1132 static __always_inline
void wake_userfault(struct userfaultfd_ctx
*ctx
,
1133 struct userfaultfd_wake_range
*range
)
1139 * To be sure waitqueue_active() is not reordered by the CPU
1140 * before the pagetable update, use an explicit SMP memory
1141 * barrier here. PT lock release or up_read(mmap_sem) still
1142 * have release semantics that can allow the
1143 * waitqueue_active() to be reordered before the pte update.
1148 * Use waitqueue_active because it's very frequent to
1149 * change the address space atomically even if there are no
1150 * userfaults yet. So we take the spinlock only when we're
1151 * sure we've userfaults to wake.
1154 seq
= read_seqcount_begin(&ctx
->refile_seq
);
1155 need_wakeup
= waitqueue_active(&ctx
->fault_pending_wqh
) ||
1156 waitqueue_active(&ctx
->fault_wqh
);
1158 } while (read_seqcount_retry(&ctx
->refile_seq
, seq
));
1160 __wake_userfault(ctx
, range
);
1163 static __always_inline
int validate_range(struct mm_struct
*mm
,
1164 __u64 start
, __u64 len
)
1166 __u64 task_size
= mm
->task_size
;
1168 if (start
& ~PAGE_MASK
)
1170 if (len
& ~PAGE_MASK
)
1174 if (start
< mmap_min_addr
)
1176 if (start
>= task_size
)
1178 if (len
> task_size
- start
)
1183 static inline bool vma_can_userfault(struct vm_area_struct
*vma
)
1185 return vma_is_anonymous(vma
) || is_vm_hugetlb_page(vma
) ||
1189 static int userfaultfd_register(struct userfaultfd_ctx
*ctx
,
1192 struct mm_struct
*mm
= ctx
->mm
;
1193 struct vm_area_struct
*vma
, *prev
, *cur
;
1195 struct uffdio_register uffdio_register
;
1196 struct uffdio_register __user
*user_uffdio_register
;
1197 unsigned long vm_flags
, new_flags
;
1199 bool non_anon_pages
;
1200 unsigned long start
, end
, vma_end
;
1202 user_uffdio_register
= (struct uffdio_register __user
*) arg
;
1205 if (copy_from_user(&uffdio_register
, user_uffdio_register
,
1206 sizeof(uffdio_register
)-sizeof(__u64
)))
1210 if (!uffdio_register
.mode
)
1212 if (uffdio_register
.mode
& ~(UFFDIO_REGISTER_MODE_MISSING
|
1213 UFFDIO_REGISTER_MODE_WP
))
1216 if (uffdio_register
.mode
& UFFDIO_REGISTER_MODE_MISSING
)
1217 vm_flags
|= VM_UFFD_MISSING
;
1218 if (uffdio_register
.mode
& UFFDIO_REGISTER_MODE_WP
) {
1219 vm_flags
|= VM_UFFD_WP
;
1221 * FIXME: remove the below error constraint by
1222 * implementing the wprotect tracking mode.
1228 ret
= validate_range(mm
, uffdio_register
.range
.start
,
1229 uffdio_register
.range
.len
);
1233 start
= uffdio_register
.range
.start
;
1234 end
= start
+ uffdio_register
.range
.len
;
1237 if (!mmget_not_zero(mm
))
1240 down_write(&mm
->mmap_sem
);
1241 vma
= find_vma_prev(mm
, start
, &prev
);
1245 /* check that there's at least one vma in the range */
1247 if (vma
->vm_start
>= end
)
1251 * If the first vma contains huge pages, make sure start address
1252 * is aligned to huge page size.
1254 if (is_vm_hugetlb_page(vma
)) {
1255 unsigned long vma_hpagesize
= vma_kernel_pagesize(vma
);
1257 if (start
& (vma_hpagesize
- 1))
1262 * Search for not compatible vmas.
1265 non_anon_pages
= false;
1266 for (cur
= vma
; cur
&& cur
->vm_start
< end
; cur
= cur
->vm_next
) {
1269 BUG_ON(!!cur
->vm_userfaultfd_ctx
.ctx
^
1270 !!(cur
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
1272 /* check not compatible vmas */
1274 if (!vma_can_userfault(cur
))
1277 * If this vma contains ending address, and huge pages
1280 if (is_vm_hugetlb_page(cur
) && end
<= cur
->vm_end
&&
1281 end
> cur
->vm_start
) {
1282 unsigned long vma_hpagesize
= vma_kernel_pagesize(cur
);
1286 if (end
& (vma_hpagesize
- 1))
1291 * Check that this vma isn't already owned by a
1292 * different userfaultfd. We can't allow more than one
1293 * userfaultfd to own a single vma simultaneously or we
1294 * wouldn't know which one to deliver the userfaults to.
1297 if (cur
->vm_userfaultfd_ctx
.ctx
&&
1298 cur
->vm_userfaultfd_ctx
.ctx
!= ctx
)
1302 * Note vmas containing huge pages
1304 if (is_vm_hugetlb_page(cur
) || vma_is_shmem(cur
))
1305 non_anon_pages
= true;
1311 if (vma
->vm_start
< start
)
1318 BUG_ON(!vma_can_userfault(vma
));
1319 BUG_ON(vma
->vm_userfaultfd_ctx
.ctx
&&
1320 vma
->vm_userfaultfd_ctx
.ctx
!= ctx
);
1323 * Nothing to do: this vma is already registered into this
1324 * userfaultfd and with the right tracking mode too.
1326 if (vma
->vm_userfaultfd_ctx
.ctx
== ctx
&&
1327 (vma
->vm_flags
& vm_flags
) == vm_flags
)
1330 if (vma
->vm_start
> start
)
1331 start
= vma
->vm_start
;
1332 vma_end
= min(end
, vma
->vm_end
);
1334 new_flags
= (vma
->vm_flags
& ~vm_flags
) | vm_flags
;
1335 prev
= vma_merge(mm
, prev
, start
, vma_end
, new_flags
,
1336 vma
->anon_vma
, vma
->vm_file
, vma
->vm_pgoff
,
1338 ((struct vm_userfaultfd_ctx
){ ctx
}));
1343 if (vma
->vm_start
< start
) {
1344 ret
= split_vma(mm
, vma
, start
, 1);
1348 if (vma
->vm_end
> end
) {
1349 ret
= split_vma(mm
, vma
, end
, 0);
1355 * In the vma_merge() successful mprotect-like case 8:
1356 * the next vma was merged into the current one and
1357 * the current one has not been updated yet.
1359 vma
->vm_flags
= new_flags
;
1360 vma
->vm_userfaultfd_ctx
.ctx
= ctx
;
1364 start
= vma
->vm_end
;
1366 } while (vma
&& vma
->vm_start
< end
);
1368 up_write(&mm
->mmap_sem
);
1372 * Now that we scanned all vmas we can already tell
1373 * userland which ioctls methods are guaranteed to
1374 * succeed on this range.
1376 if (put_user(non_anon_pages
? UFFD_API_RANGE_IOCTLS_BASIC
:
1377 UFFD_API_RANGE_IOCTLS
,
1378 &user_uffdio_register
->ioctls
))
1385 static int userfaultfd_unregister(struct userfaultfd_ctx
*ctx
,
1388 struct mm_struct
*mm
= ctx
->mm
;
1389 struct vm_area_struct
*vma
, *prev
, *cur
;
1391 struct uffdio_range uffdio_unregister
;
1392 unsigned long new_flags
;
1394 unsigned long start
, end
, vma_end
;
1395 const void __user
*buf
= (void __user
*)arg
;
1398 if (copy_from_user(&uffdio_unregister
, buf
, sizeof(uffdio_unregister
)))
1401 ret
= validate_range(mm
, uffdio_unregister
.start
,
1402 uffdio_unregister
.len
);
1406 start
= uffdio_unregister
.start
;
1407 end
= start
+ uffdio_unregister
.len
;
1410 if (!mmget_not_zero(mm
))
1413 down_write(&mm
->mmap_sem
);
1414 vma
= find_vma_prev(mm
, start
, &prev
);
1418 /* check that there's at least one vma in the range */
1420 if (vma
->vm_start
>= end
)
1424 * If the first vma contains huge pages, make sure start address
1425 * is aligned to huge page size.
1427 if (is_vm_hugetlb_page(vma
)) {
1428 unsigned long vma_hpagesize
= vma_kernel_pagesize(vma
);
1430 if (start
& (vma_hpagesize
- 1))
1435 * Search for not compatible vmas.
1439 for (cur
= vma
; cur
&& cur
->vm_start
< end
; cur
= cur
->vm_next
) {
1442 BUG_ON(!!cur
->vm_userfaultfd_ctx
.ctx
^
1443 !!(cur
->vm_flags
& (VM_UFFD_MISSING
| VM_UFFD_WP
)));
1446 * Check not compatible vmas, not strictly required
1447 * here as not compatible vmas cannot have an
1448 * userfaultfd_ctx registered on them, but this
1449 * provides for more strict behavior to notice
1450 * unregistration errors.
1452 if (!vma_can_userfault(cur
))
1459 if (vma
->vm_start
< start
)
1466 BUG_ON(!vma_can_userfault(vma
));
1469 * Nothing to do: this vma is already registered into this
1470 * userfaultfd and with the right tracking mode too.
1472 if (!vma
->vm_userfaultfd_ctx
.ctx
)
1475 if (vma
->vm_start
> start
)
1476 start
= vma
->vm_start
;
1477 vma_end
= min(end
, vma
->vm_end
);
1479 if (userfaultfd_missing(vma
)) {
1481 * Wake any concurrent pending userfault while
1482 * we unregister, so they will not hang
1483 * permanently and it avoids userland to call
1484 * UFFDIO_WAKE explicitly.
1486 struct userfaultfd_wake_range range
;
1487 range
.start
= start
;
1488 range
.len
= vma_end
- start
;
1489 wake_userfault(vma
->vm_userfaultfd_ctx
.ctx
, &range
);
1492 new_flags
= vma
->vm_flags
& ~(VM_UFFD_MISSING
| VM_UFFD_WP
);
1493 prev
= vma_merge(mm
, prev
, start
, vma_end
, new_flags
,
1494 vma
->anon_vma
, vma
->vm_file
, vma
->vm_pgoff
,
1501 if (vma
->vm_start
< start
) {
1502 ret
= split_vma(mm
, vma
, start
, 1);
1506 if (vma
->vm_end
> end
) {
1507 ret
= split_vma(mm
, vma
, end
, 0);
1513 * In the vma_merge() successful mprotect-like case 8:
1514 * the next vma was merged into the current one and
1515 * the current one has not been updated yet.
1517 vma
->vm_flags
= new_flags
;
1518 vma
->vm_userfaultfd_ctx
= NULL_VM_UFFD_CTX
;
1522 start
= vma
->vm_end
;
1524 } while (vma
&& vma
->vm_start
< end
);
1526 up_write(&mm
->mmap_sem
);
1533 * userfaultfd_wake may be used in combination with the
1534 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1536 static int userfaultfd_wake(struct userfaultfd_ctx
*ctx
,
1540 struct uffdio_range uffdio_wake
;
1541 struct userfaultfd_wake_range range
;
1542 const void __user
*buf
= (void __user
*)arg
;
1545 if (copy_from_user(&uffdio_wake
, buf
, sizeof(uffdio_wake
)))
1548 ret
= validate_range(ctx
->mm
, uffdio_wake
.start
, uffdio_wake
.len
);
1552 range
.start
= uffdio_wake
.start
;
1553 range
.len
= uffdio_wake
.len
;
1556 * len == 0 means wake all and we don't want to wake all here,
1557 * so check it again to be sure.
1559 VM_BUG_ON(!range
.len
);
1561 wake_userfault(ctx
, &range
);
1568 static int userfaultfd_copy(struct userfaultfd_ctx
*ctx
,
1572 struct uffdio_copy uffdio_copy
;
1573 struct uffdio_copy __user
*user_uffdio_copy
;
1574 struct userfaultfd_wake_range range
;
1576 user_uffdio_copy
= (struct uffdio_copy __user
*) arg
;
1579 if (copy_from_user(&uffdio_copy
, user_uffdio_copy
,
1580 /* don't copy "copy" last field */
1581 sizeof(uffdio_copy
)-sizeof(__s64
)))
1584 ret
= validate_range(ctx
->mm
, uffdio_copy
.dst
, uffdio_copy
.len
);
1588 * double check for wraparound just in case. copy_from_user()
1589 * will later check uffdio_copy.src + uffdio_copy.len to fit
1590 * in the userland range.
1593 if (uffdio_copy
.src
+ uffdio_copy
.len
<= uffdio_copy
.src
)
1595 if (uffdio_copy
.mode
& ~UFFDIO_COPY_MODE_DONTWAKE
)
1597 if (mmget_not_zero(ctx
->mm
)) {
1598 ret
= mcopy_atomic(ctx
->mm
, uffdio_copy
.dst
, uffdio_copy
.src
,
1604 if (unlikely(put_user(ret
, &user_uffdio_copy
->copy
)))
1609 /* len == 0 would wake all */
1611 if (!(uffdio_copy
.mode
& UFFDIO_COPY_MODE_DONTWAKE
)) {
1612 range
.start
= uffdio_copy
.dst
;
1613 wake_userfault(ctx
, &range
);
1615 ret
= range
.len
== uffdio_copy
.len
? 0 : -EAGAIN
;
1620 static int userfaultfd_zeropage(struct userfaultfd_ctx
*ctx
,
1624 struct uffdio_zeropage uffdio_zeropage
;
1625 struct uffdio_zeropage __user
*user_uffdio_zeropage
;
1626 struct userfaultfd_wake_range range
;
1628 user_uffdio_zeropage
= (struct uffdio_zeropage __user
*) arg
;
1631 if (copy_from_user(&uffdio_zeropage
, user_uffdio_zeropage
,
1632 /* don't copy "zeropage" last field */
1633 sizeof(uffdio_zeropage
)-sizeof(__s64
)))
1636 ret
= validate_range(ctx
->mm
, uffdio_zeropage
.range
.start
,
1637 uffdio_zeropage
.range
.len
);
1641 if (uffdio_zeropage
.mode
& ~UFFDIO_ZEROPAGE_MODE_DONTWAKE
)
1644 if (mmget_not_zero(ctx
->mm
)) {
1645 ret
= mfill_zeropage(ctx
->mm
, uffdio_zeropage
.range
.start
,
1646 uffdio_zeropage
.range
.len
);
1649 if (unlikely(put_user(ret
, &user_uffdio_zeropage
->zeropage
)))
1653 /* len == 0 would wake all */
1656 if (!(uffdio_zeropage
.mode
& UFFDIO_ZEROPAGE_MODE_DONTWAKE
)) {
1657 range
.start
= uffdio_zeropage
.range
.start
;
1658 wake_userfault(ctx
, &range
);
1660 ret
= range
.len
== uffdio_zeropage
.range
.len
? 0 : -EAGAIN
;
1665 static inline unsigned int uffd_ctx_features(__u64 user_features
)
1668 * For the current set of features the bits just coincide
1670 return (unsigned int)user_features
;
1674 * userland asks for a certain API version and we return which bits
1675 * and ioctl commands are implemented in this kernel for such API
1676 * version or -EINVAL if unknown.
1678 static int userfaultfd_api(struct userfaultfd_ctx
*ctx
,
1681 struct uffdio_api uffdio_api
;
1682 void __user
*buf
= (void __user
*)arg
;
1687 if (ctx
->state
!= UFFD_STATE_WAIT_API
)
1690 if (copy_from_user(&uffdio_api
, buf
, sizeof(uffdio_api
)))
1692 features
= uffdio_api
.features
;
1693 if (uffdio_api
.api
!= UFFD_API
|| (features
& ~UFFD_API_FEATURES
)) {
1694 memset(&uffdio_api
, 0, sizeof(uffdio_api
));
1695 if (copy_to_user(buf
, &uffdio_api
, sizeof(uffdio_api
)))
1700 /* report all available features and ioctls to userland */
1701 uffdio_api
.features
= UFFD_API_FEATURES
;
1702 uffdio_api
.ioctls
= UFFD_API_IOCTLS
;
1704 if (copy_to_user(buf
, &uffdio_api
, sizeof(uffdio_api
)))
1706 ctx
->state
= UFFD_STATE_RUNNING
;
1707 /* only enable the requested features for this uffd context */
1708 ctx
->features
= uffd_ctx_features(features
);
1714 static long userfaultfd_ioctl(struct file
*file
, unsigned cmd
,
1718 struct userfaultfd_ctx
*ctx
= file
->private_data
;
1720 if (cmd
!= UFFDIO_API
&& ctx
->state
== UFFD_STATE_WAIT_API
)
1725 ret
= userfaultfd_api(ctx
, arg
);
1727 case UFFDIO_REGISTER
:
1728 ret
= userfaultfd_register(ctx
, arg
);
1730 case UFFDIO_UNREGISTER
:
1731 ret
= userfaultfd_unregister(ctx
, arg
);
1734 ret
= userfaultfd_wake(ctx
, arg
);
1737 ret
= userfaultfd_copy(ctx
, arg
);
1739 case UFFDIO_ZEROPAGE
:
1740 ret
= userfaultfd_zeropage(ctx
, arg
);
1746 #ifdef CONFIG_PROC_FS
1747 static void userfaultfd_show_fdinfo(struct seq_file
*m
, struct file
*f
)
1749 struct userfaultfd_ctx
*ctx
= f
->private_data
;
1751 struct userfaultfd_wait_queue
*uwq
;
1752 unsigned long pending
= 0, total
= 0;
1754 spin_lock(&ctx
->fault_pending_wqh
.lock
);
1755 list_for_each_entry(wq
, &ctx
->fault_pending_wqh
.task_list
, task_list
) {
1756 uwq
= container_of(wq
, struct userfaultfd_wait_queue
, wq
);
1760 list_for_each_entry(wq
, &ctx
->fault_wqh
.task_list
, task_list
) {
1761 uwq
= container_of(wq
, struct userfaultfd_wait_queue
, wq
);
1764 spin_unlock(&ctx
->fault_pending_wqh
.lock
);
1767 * If more protocols will be added, there will be all shown
1768 * separated by a space. Like this:
1769 * protocols: aa:... bb:...
1771 seq_printf(m
, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1772 pending
, total
, UFFD_API
, ctx
->features
,
1773 UFFD_API_IOCTLS
|UFFD_API_RANGE_IOCTLS
);
1777 static const struct file_operations userfaultfd_fops
= {
1778 #ifdef CONFIG_PROC_FS
1779 .show_fdinfo
= userfaultfd_show_fdinfo
,
1781 .release
= userfaultfd_release
,
1782 .poll
= userfaultfd_poll
,
1783 .read
= userfaultfd_read
,
1784 .unlocked_ioctl
= userfaultfd_ioctl
,
1785 .compat_ioctl
= userfaultfd_ioctl
,
1786 .llseek
= noop_llseek
,
1789 static void init_once_userfaultfd_ctx(void *mem
)
1791 struct userfaultfd_ctx
*ctx
= (struct userfaultfd_ctx
*) mem
;
1793 init_waitqueue_head(&ctx
->fault_pending_wqh
);
1794 init_waitqueue_head(&ctx
->fault_wqh
);
1795 init_waitqueue_head(&ctx
->event_wqh
);
1796 init_waitqueue_head(&ctx
->fd_wqh
);
1797 seqcount_init(&ctx
->refile_seq
);
1801 * userfaultfd_file_create - Creates a userfaultfd file pointer.
1802 * @flags: Flags for the userfaultfd file.
1804 * This function creates a userfaultfd file pointer, w/out installing
1805 * it into the fd table. This is useful when the userfaultfd file is
1806 * used during the initialization of data structures that require
1807 * extra setup after the userfaultfd creation. So the userfaultfd
1808 * creation is split into the file pointer creation phase, and the
1809 * file descriptor installation phase. In this way races with
1810 * userspace closing the newly installed file descriptor can be
1811 * avoided. Returns a userfaultfd file pointer, or a proper error
1814 static struct file
*userfaultfd_file_create(int flags
)
1817 struct userfaultfd_ctx
*ctx
;
1819 BUG_ON(!current
->mm
);
1821 /* Check the UFFD_* constants for consistency. */
1822 BUILD_BUG_ON(UFFD_CLOEXEC
!= O_CLOEXEC
);
1823 BUILD_BUG_ON(UFFD_NONBLOCK
!= O_NONBLOCK
);
1825 file
= ERR_PTR(-EINVAL
);
1826 if (flags
& ~UFFD_SHARED_FCNTL_FLAGS
)
1829 file
= ERR_PTR(-ENOMEM
);
1830 ctx
= kmem_cache_alloc(userfaultfd_ctx_cachep
, GFP_KERNEL
);
1834 atomic_set(&ctx
->refcount
, 1);
1837 ctx
->state
= UFFD_STATE_WAIT_API
;
1838 ctx
->released
= false;
1839 ctx
->mm
= current
->mm
;
1840 /* prevent the mm struct to be freed */
1843 file
= anon_inode_getfile("[userfaultfd]", &userfaultfd_fops
, ctx
,
1844 O_RDWR
| (flags
& UFFD_SHARED_FCNTL_FLAGS
));
1847 kmem_cache_free(userfaultfd_ctx_cachep
, ctx
);
1853 SYSCALL_DEFINE1(userfaultfd
, int, flags
)
1858 error
= get_unused_fd_flags(flags
& UFFD_SHARED_FCNTL_FLAGS
);
1863 file
= userfaultfd_file_create(flags
);
1865 error
= PTR_ERR(file
);
1866 goto err_put_unused_fd
;
1868 fd_install(fd
, file
);
1878 static int __init
userfaultfd_init(void)
1880 userfaultfd_ctx_cachep
= kmem_cache_create("userfaultfd_ctx_cache",
1881 sizeof(struct userfaultfd_ctx
),
1883 SLAB_HWCACHE_ALIGN
|SLAB_PANIC
,
1884 init_once_userfaultfd_ctx
);
1887 __initcall(userfaultfd_init
);