Merge branch 'for-5.2' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup
[sfrench/cifs-2.6.git] / fs / userfaultfd.c
1 /*
2  *  fs/userfaultfd.c
3  *
4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
5  *  Copyright (C) 2008-2009 Red Hat, Inc.
6  *  Copyright (C) 2015  Red Hat, Inc.
7  *
8  *  This work is licensed under the terms of the GNU GPL, version 2. See
9  *  the COPYING file in the top-level directory.
10  *
11  *  Some part derived from fs/eventfd.c (anon inode setup) and
12  *  mm/ksm.c (mm hashing).
13  */
14
15 #include <linux/list.h>
16 #include <linux/hashtable.h>
17 #include <linux/sched/signal.h>
18 #include <linux/sched/mm.h>
19 #include <linux/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>
32
33 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
34
35 enum userfaultfd_state {
36         UFFD_STATE_WAIT_API,
37         UFFD_STATE_RUNNING,
38 };
39
40 /*
41  * Start with fault_pending_wqh and fault_wqh so they're more likely
42  * to be in the same cacheline.
43  */
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 */
56         refcount_t refcount;
57         /* userfaultfd syscall flags */
58         unsigned int flags;
59         /* features requested from the userspace */
60         unsigned int features;
61         /* state machine */
62         enum userfaultfd_state state;
63         /* released */
64         bool released;
65         /* memory mappings are changing because of non-cooperative event */
66         bool mmap_changing;
67         /* mm with one ore more vmas attached to this userfaultfd_ctx */
68         struct mm_struct *mm;
69 };
70
71 struct userfaultfd_fork_ctx {
72         struct userfaultfd_ctx *orig;
73         struct userfaultfd_ctx *new;
74         struct list_head list;
75 };
76
77 struct userfaultfd_unmap_ctx {
78         struct userfaultfd_ctx *ctx;
79         unsigned long start;
80         unsigned long end;
81         struct list_head list;
82 };
83
84 struct userfaultfd_wait_queue {
85         struct uffd_msg msg;
86         wait_queue_entry_t wq;
87         struct userfaultfd_ctx *ctx;
88         bool waken;
89 };
90
91 struct userfaultfd_wake_range {
92         unsigned long start;
93         unsigned long len;
94 };
95
96 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
97                                      int wake_flags, void *key)
98 {
99         struct userfaultfd_wake_range *range = key;
100         int ret;
101         struct userfaultfd_wait_queue *uwq;
102         unsigned long start, len;
103
104         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
105         ret = 0;
106         /* len == 0 means wake all */
107         start = range->start;
108         len = range->len;
109         if (len && (start > uwq->msg.arg.pagefault.address ||
110                     start + len <= uwq->msg.arg.pagefault.address))
111                 goto out;
112         WRITE_ONCE(uwq->waken, true);
113         /*
114          * The Program-Order guarantees provided by the scheduler
115          * ensure uwq->waken is visible before the task is woken.
116          */
117         ret = wake_up_state(wq->private, mode);
118         if (ret) {
119                 /*
120                  * Wake only once, autoremove behavior.
121                  *
122                  * After the effect of list_del_init is visible to the other
123                  * CPUs, the waitqueue may disappear from under us, see the
124                  * !list_empty_careful() in handle_userfault().
125                  *
126                  * try_to_wake_up() has an implicit smp_mb(), and the
127                  * wq->private is read before calling the extern function
128                  * "wake_up_state" (which in turns calls try_to_wake_up).
129                  */
130                 list_del_init(&wq->entry);
131         }
132 out:
133         return ret;
134 }
135
136 /**
137  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
138  * context.
139  * @ctx: [in] Pointer to the userfaultfd context.
140  */
141 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
142 {
143         refcount_inc(&ctx->refcount);
144 }
145
146 /**
147  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
148  * context.
149  * @ctx: [in] Pointer to userfaultfd context.
150  *
151  * The userfaultfd context reference must have been previously acquired either
152  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
153  */
154 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
155 {
156         if (refcount_dec_and_test(&ctx->refcount)) {
157                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
158                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
159                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
160                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
161                 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
162                 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
163                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
164                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
165                 mmdrop(ctx->mm);
166                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
167         }
168 }
169
170 static inline void msg_init(struct uffd_msg *msg)
171 {
172         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
173         /*
174          * Must use memset to zero out the paddings or kernel data is
175          * leaked to userland.
176          */
177         memset(msg, 0, sizeof(struct uffd_msg));
178 }
179
180 static inline struct uffd_msg userfault_msg(unsigned long address,
181                                             unsigned int flags,
182                                             unsigned long reason,
183                                             unsigned int features)
184 {
185         struct uffd_msg msg;
186         msg_init(&msg);
187         msg.event = UFFD_EVENT_PAGEFAULT;
188         msg.arg.pagefault.address = address;
189         if (flags & FAULT_FLAG_WRITE)
190                 /*
191                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
192                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
193                  * was not set in a UFFD_EVENT_PAGEFAULT, it means it
194                  * was a read fault, otherwise if set it means it's
195                  * a write fault.
196                  */
197                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
198         if (reason & VM_UFFD_WP)
199                 /*
200                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
201                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
202                  * not set in a UFFD_EVENT_PAGEFAULT, it means it was
203                  * a missing fault, otherwise if set it means it's a
204                  * write protect fault.
205                  */
206                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
207         if (features & UFFD_FEATURE_THREAD_ID)
208                 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
209         return msg;
210 }
211
212 #ifdef CONFIG_HUGETLB_PAGE
213 /*
214  * Same functionality as userfaultfd_must_wait below with modifications for
215  * hugepmd ranges.
216  */
217 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
218                                          struct vm_area_struct *vma,
219                                          unsigned long address,
220                                          unsigned long flags,
221                                          unsigned long reason)
222 {
223         struct mm_struct *mm = ctx->mm;
224         pte_t *ptep, pte;
225         bool ret = true;
226
227         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
228
229         ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
230
231         if (!ptep)
232                 goto out;
233
234         ret = false;
235         pte = huge_ptep_get(ptep);
236
237         /*
238          * Lockless access: we're in a wait_event so it's ok if it
239          * changes under us.
240          */
241         if (huge_pte_none(pte))
242                 ret = true;
243         if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
244                 ret = true;
245 out:
246         return ret;
247 }
248 #else
249 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
250                                          struct vm_area_struct *vma,
251                                          unsigned long address,
252                                          unsigned long flags,
253                                          unsigned long reason)
254 {
255         return false;   /* should never get here */
256 }
257 #endif /* CONFIG_HUGETLB_PAGE */
258
259 /*
260  * Verify the pagetables are still not ok after having reigstered into
261  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
262  * userfault that has already been resolved, if userfaultfd_read and
263  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
264  * threads.
265  */
266 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
267                                          unsigned long address,
268                                          unsigned long flags,
269                                          unsigned long reason)
270 {
271         struct mm_struct *mm = ctx->mm;
272         pgd_t *pgd;
273         p4d_t *p4d;
274         pud_t *pud;
275         pmd_t *pmd, _pmd;
276         pte_t *pte;
277         bool ret = true;
278
279         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
280
281         pgd = pgd_offset(mm, address);
282         if (!pgd_present(*pgd))
283                 goto out;
284         p4d = p4d_offset(pgd, address);
285         if (!p4d_present(*p4d))
286                 goto out;
287         pud = pud_offset(p4d, address);
288         if (!pud_present(*pud))
289                 goto out;
290         pmd = pmd_offset(pud, address);
291         /*
292          * READ_ONCE must function as a barrier with narrower scope
293          * and it must be equivalent to:
294          *      _pmd = *pmd; barrier();
295          *
296          * This is to deal with the instability (as in
297          * pmd_trans_unstable) of the pmd.
298          */
299         _pmd = READ_ONCE(*pmd);
300         if (pmd_none(_pmd))
301                 goto out;
302
303         ret = false;
304         if (!pmd_present(_pmd))
305                 goto out;
306
307         if (pmd_trans_huge(_pmd))
308                 goto out;
309
310         /*
311          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
312          * and use the standard pte_offset_map() instead of parsing _pmd.
313          */
314         pte = pte_offset_map(pmd, address);
315         /*
316          * Lockless access: we're in a wait_event so it's ok if it
317          * changes under us.
318          */
319         if (pte_none(*pte))
320                 ret = true;
321         pte_unmap(pte);
322
323 out:
324         return ret;
325 }
326
327 /*
328  * The locking rules involved in returning VM_FAULT_RETRY depending on
329  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
330  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
331  * recommendation in __lock_page_or_retry is not an understatement.
332  *
333  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
334  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
335  * not set.
336  *
337  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
338  * set, VM_FAULT_RETRY can still be returned if and only if there are
339  * fatal_signal_pending()s, and the mmap_sem must be released before
340  * returning it.
341  */
342 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
343 {
344         struct mm_struct *mm = vmf->vma->vm_mm;
345         struct userfaultfd_ctx *ctx;
346         struct userfaultfd_wait_queue uwq;
347         vm_fault_t ret = VM_FAULT_SIGBUS;
348         bool must_wait, return_to_userland;
349         long blocking_state;
350
351         /*
352          * We don't do userfault handling for the final child pid update.
353          *
354          * We also don't do userfault handling during
355          * coredumping. hugetlbfs has the special
356          * follow_hugetlb_page() to skip missing pages in the
357          * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
358          * the no_page_table() helper in follow_page_mask(), but the
359          * shmem_vm_ops->fault method is invoked even during
360          * coredumping without mmap_sem and it ends up here.
361          */
362         if (current->flags & (PF_EXITING|PF_DUMPCORE))
363                 goto out;
364
365         /*
366          * Coredumping runs without mmap_sem so we can only check that
367          * the mmap_sem is held, if PF_DUMPCORE was not set.
368          */
369         WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
370
371         ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
372         if (!ctx)
373                 goto out;
374
375         BUG_ON(ctx->mm != mm);
376
377         VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
378         VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
379
380         if (ctx->features & UFFD_FEATURE_SIGBUS)
381                 goto out;
382
383         /*
384          * If it's already released don't get it. This avoids to loop
385          * in __get_user_pages if userfaultfd_release waits on the
386          * caller of handle_userfault to release the mmap_sem.
387          */
388         if (unlikely(READ_ONCE(ctx->released))) {
389                 /*
390                  * Don't return VM_FAULT_SIGBUS in this case, so a non
391                  * cooperative manager can close the uffd after the
392                  * last UFFDIO_COPY, without risking to trigger an
393                  * involuntary SIGBUS if the process was starting the
394                  * userfaultfd while the userfaultfd was still armed
395                  * (but after the last UFFDIO_COPY). If the uffd
396                  * wasn't already closed when the userfault reached
397                  * this point, that would normally be solved by
398                  * userfaultfd_must_wait returning 'false'.
399                  *
400                  * If we were to return VM_FAULT_SIGBUS here, the non
401                  * cooperative manager would be instead forced to
402                  * always call UFFDIO_UNREGISTER before it can safely
403                  * close the uffd.
404                  */
405                 ret = VM_FAULT_NOPAGE;
406                 goto out;
407         }
408
409         /*
410          * Check that we can return VM_FAULT_RETRY.
411          *
412          * NOTE: it should become possible to return VM_FAULT_RETRY
413          * even if FAULT_FLAG_TRIED is set without leading to gup()
414          * -EBUSY failures, if the userfaultfd is to be extended for
415          * VM_UFFD_WP tracking and we intend to arm the userfault
416          * without first stopping userland access to the memory. For
417          * VM_UFFD_MISSING userfaults this is enough for now.
418          */
419         if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
420                 /*
421                  * Validate the invariant that nowait must allow retry
422                  * to be sure not to return SIGBUS erroneously on
423                  * nowait invocations.
424                  */
425                 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
426 #ifdef CONFIG_DEBUG_VM
427                 if (printk_ratelimit()) {
428                         printk(KERN_WARNING
429                                "FAULT_FLAG_ALLOW_RETRY missing %x\n",
430                                vmf->flags);
431                         dump_stack();
432                 }
433 #endif
434                 goto out;
435         }
436
437         /*
438          * Handle nowait, not much to do other than tell it to retry
439          * and wait.
440          */
441         ret = VM_FAULT_RETRY;
442         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
443                 goto out;
444
445         /* take the reference before dropping the mmap_sem */
446         userfaultfd_ctx_get(ctx);
447
448         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
449         uwq.wq.private = current;
450         uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
451                         ctx->features);
452         uwq.ctx = ctx;
453         uwq.waken = false;
454
455         return_to_userland =
456                 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
457                 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
458         blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
459                          TASK_KILLABLE;
460
461         spin_lock(&ctx->fault_pending_wqh.lock);
462         /*
463          * After the __add_wait_queue the uwq is visible to userland
464          * through poll/read().
465          */
466         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
467         /*
468          * The smp_mb() after __set_current_state prevents the reads
469          * following the spin_unlock to happen before the list_add in
470          * __add_wait_queue.
471          */
472         set_current_state(blocking_state);
473         spin_unlock(&ctx->fault_pending_wqh.lock);
474
475         if (!is_vm_hugetlb_page(vmf->vma))
476                 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
477                                                   reason);
478         else
479                 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
480                                                        vmf->address,
481                                                        vmf->flags, reason);
482         up_read(&mm->mmap_sem);
483
484         if (likely(must_wait && !READ_ONCE(ctx->released) &&
485                    (return_to_userland ? !signal_pending(current) :
486                     !fatal_signal_pending(current)))) {
487                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
488                 schedule();
489                 ret |= VM_FAULT_MAJOR;
490
491                 /*
492                  * False wakeups can orginate even from rwsem before
493                  * up_read() however userfaults will wait either for a
494                  * targeted wakeup on the specific uwq waitqueue from
495                  * wake_userfault() or for signals or for uffd
496                  * release.
497                  */
498                 while (!READ_ONCE(uwq.waken)) {
499                         /*
500                          * This needs the full smp_store_mb()
501                          * guarantee as the state write must be
502                          * visible to other CPUs before reading
503                          * uwq.waken from other CPUs.
504                          */
505                         set_current_state(blocking_state);
506                         if (READ_ONCE(uwq.waken) ||
507                             READ_ONCE(ctx->released) ||
508                             (return_to_userland ? signal_pending(current) :
509                              fatal_signal_pending(current)))
510                                 break;
511                         schedule();
512                 }
513         }
514
515         __set_current_state(TASK_RUNNING);
516
517         if (return_to_userland) {
518                 if (signal_pending(current) &&
519                     !fatal_signal_pending(current)) {
520                         /*
521                          * If we got a SIGSTOP or SIGCONT and this is
522                          * a normal userland page fault, just let
523                          * userland return so the signal will be
524                          * handled and gdb debugging works.  The page
525                          * fault code immediately after we return from
526                          * this function is going to release the
527                          * mmap_sem and it's not depending on it
528                          * (unlike gup would if we were not to return
529                          * VM_FAULT_RETRY).
530                          *
531                          * If a fatal signal is pending we still take
532                          * the streamlined VM_FAULT_RETRY failure path
533                          * and there's no need to retake the mmap_sem
534                          * in such case.
535                          */
536                         down_read(&mm->mmap_sem);
537                         ret = VM_FAULT_NOPAGE;
538                 }
539         }
540
541         /*
542          * Here we race with the list_del; list_add in
543          * userfaultfd_ctx_read(), however because we don't ever run
544          * list_del_init() to refile across the two lists, the prev
545          * and next pointers will never point to self. list_add also
546          * would never let any of the two pointers to point to
547          * self. So list_empty_careful won't risk to see both pointers
548          * pointing to self at any time during the list refile. The
549          * only case where list_del_init() is called is the full
550          * removal in the wake function and there we don't re-list_add
551          * and it's fine not to block on the spinlock. The uwq on this
552          * kernel stack can be released after the list_del_init.
553          */
554         if (!list_empty_careful(&uwq.wq.entry)) {
555                 spin_lock(&ctx->fault_pending_wqh.lock);
556                 /*
557                  * No need of list_del_init(), the uwq on the stack
558                  * will be freed shortly anyway.
559                  */
560                 list_del(&uwq.wq.entry);
561                 spin_unlock(&ctx->fault_pending_wqh.lock);
562         }
563
564         /*
565          * ctx may go away after this if the userfault pseudo fd is
566          * already released.
567          */
568         userfaultfd_ctx_put(ctx);
569
570 out:
571         return ret;
572 }
573
574 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
575                                               struct userfaultfd_wait_queue *ewq)
576 {
577         struct userfaultfd_ctx *release_new_ctx;
578
579         if (WARN_ON_ONCE(current->flags & PF_EXITING))
580                 goto out;
581
582         ewq->ctx = ctx;
583         init_waitqueue_entry(&ewq->wq, current);
584         release_new_ctx = NULL;
585
586         spin_lock(&ctx->event_wqh.lock);
587         /*
588          * After the __add_wait_queue the uwq is visible to userland
589          * through poll/read().
590          */
591         __add_wait_queue(&ctx->event_wqh, &ewq->wq);
592         for (;;) {
593                 set_current_state(TASK_KILLABLE);
594                 if (ewq->msg.event == 0)
595                         break;
596                 if (READ_ONCE(ctx->released) ||
597                     fatal_signal_pending(current)) {
598                         /*
599                          * &ewq->wq may be queued in fork_event, but
600                          * __remove_wait_queue ignores the head
601                          * parameter. It would be a problem if it
602                          * didn't.
603                          */
604                         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
605                         if (ewq->msg.event == UFFD_EVENT_FORK) {
606                                 struct userfaultfd_ctx *new;
607
608                                 new = (struct userfaultfd_ctx *)
609                                         (unsigned long)
610                                         ewq->msg.arg.reserved.reserved1;
611                                 release_new_ctx = new;
612                         }
613                         break;
614                 }
615
616                 spin_unlock(&ctx->event_wqh.lock);
617
618                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
619                 schedule();
620
621                 spin_lock(&ctx->event_wqh.lock);
622         }
623         __set_current_state(TASK_RUNNING);
624         spin_unlock(&ctx->event_wqh.lock);
625
626         if (release_new_ctx) {
627                 struct vm_area_struct *vma;
628                 struct mm_struct *mm = release_new_ctx->mm;
629
630                 /* the various vma->vm_userfaultfd_ctx still points to it */
631                 down_write(&mm->mmap_sem);
632                 /* no task can run (and in turn coredump) yet */
633                 VM_WARN_ON(!mmget_still_valid(mm));
634                 for (vma = mm->mmap; vma; vma = vma->vm_next)
635                         if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
636                                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
637                                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
638                         }
639                 up_write(&mm->mmap_sem);
640
641                 userfaultfd_ctx_put(release_new_ctx);
642         }
643
644         /*
645          * ctx may go away after this if the userfault pseudo fd is
646          * already released.
647          */
648 out:
649         WRITE_ONCE(ctx->mmap_changing, false);
650         userfaultfd_ctx_put(ctx);
651 }
652
653 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
654                                        struct userfaultfd_wait_queue *ewq)
655 {
656         ewq->msg.event = 0;
657         wake_up_locked(&ctx->event_wqh);
658         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
659 }
660
661 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
662 {
663         struct userfaultfd_ctx *ctx = NULL, *octx;
664         struct userfaultfd_fork_ctx *fctx;
665
666         octx = vma->vm_userfaultfd_ctx.ctx;
667         if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
668                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
669                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
670                 return 0;
671         }
672
673         list_for_each_entry(fctx, fcs, list)
674                 if (fctx->orig == octx) {
675                         ctx = fctx->new;
676                         break;
677                 }
678
679         if (!ctx) {
680                 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
681                 if (!fctx)
682                         return -ENOMEM;
683
684                 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
685                 if (!ctx) {
686                         kfree(fctx);
687                         return -ENOMEM;
688                 }
689
690                 refcount_set(&ctx->refcount, 1);
691                 ctx->flags = octx->flags;
692                 ctx->state = UFFD_STATE_RUNNING;
693                 ctx->features = octx->features;
694                 ctx->released = false;
695                 ctx->mmap_changing = false;
696                 ctx->mm = vma->vm_mm;
697                 mmgrab(ctx->mm);
698
699                 userfaultfd_ctx_get(octx);
700                 WRITE_ONCE(octx->mmap_changing, true);
701                 fctx->orig = octx;
702                 fctx->new = ctx;
703                 list_add_tail(&fctx->list, fcs);
704         }
705
706         vma->vm_userfaultfd_ctx.ctx = ctx;
707         return 0;
708 }
709
710 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
711 {
712         struct userfaultfd_ctx *ctx = fctx->orig;
713         struct userfaultfd_wait_queue ewq;
714
715         msg_init(&ewq.msg);
716
717         ewq.msg.event = UFFD_EVENT_FORK;
718         ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
719
720         userfaultfd_event_wait_completion(ctx, &ewq);
721 }
722
723 void dup_userfaultfd_complete(struct list_head *fcs)
724 {
725         struct userfaultfd_fork_ctx *fctx, *n;
726
727         list_for_each_entry_safe(fctx, n, fcs, list) {
728                 dup_fctx(fctx);
729                 list_del(&fctx->list);
730                 kfree(fctx);
731         }
732 }
733
734 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
735                              struct vm_userfaultfd_ctx *vm_ctx)
736 {
737         struct userfaultfd_ctx *ctx;
738
739         ctx = vma->vm_userfaultfd_ctx.ctx;
740
741         if (!ctx)
742                 return;
743
744         if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
745                 vm_ctx->ctx = ctx;
746                 userfaultfd_ctx_get(ctx);
747                 WRITE_ONCE(ctx->mmap_changing, true);
748         } else {
749                 /* Drop uffd context if remap feature not enabled */
750                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
751                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
752         }
753 }
754
755 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
756                                  unsigned long from, unsigned long to,
757                                  unsigned long len)
758 {
759         struct userfaultfd_ctx *ctx = vm_ctx->ctx;
760         struct userfaultfd_wait_queue ewq;
761
762         if (!ctx)
763                 return;
764
765         if (to & ~PAGE_MASK) {
766                 userfaultfd_ctx_put(ctx);
767                 return;
768         }
769
770         msg_init(&ewq.msg);
771
772         ewq.msg.event = UFFD_EVENT_REMAP;
773         ewq.msg.arg.remap.from = from;
774         ewq.msg.arg.remap.to = to;
775         ewq.msg.arg.remap.len = len;
776
777         userfaultfd_event_wait_completion(ctx, &ewq);
778 }
779
780 bool userfaultfd_remove(struct vm_area_struct *vma,
781                         unsigned long start, unsigned long end)
782 {
783         struct mm_struct *mm = vma->vm_mm;
784         struct userfaultfd_ctx *ctx;
785         struct userfaultfd_wait_queue ewq;
786
787         ctx = vma->vm_userfaultfd_ctx.ctx;
788         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
789                 return true;
790
791         userfaultfd_ctx_get(ctx);
792         WRITE_ONCE(ctx->mmap_changing, true);
793         up_read(&mm->mmap_sem);
794
795         msg_init(&ewq.msg);
796
797         ewq.msg.event = UFFD_EVENT_REMOVE;
798         ewq.msg.arg.remove.start = start;
799         ewq.msg.arg.remove.end = end;
800
801         userfaultfd_event_wait_completion(ctx, &ewq);
802
803         return false;
804 }
805
806 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
807                           unsigned long start, unsigned long end)
808 {
809         struct userfaultfd_unmap_ctx *unmap_ctx;
810
811         list_for_each_entry(unmap_ctx, unmaps, list)
812                 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
813                     unmap_ctx->end == end)
814                         return true;
815
816         return false;
817 }
818
819 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
820                            unsigned long start, unsigned long end,
821                            struct list_head *unmaps)
822 {
823         for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
824                 struct userfaultfd_unmap_ctx *unmap_ctx;
825                 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
826
827                 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
828                     has_unmap_ctx(ctx, unmaps, start, end))
829                         continue;
830
831                 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
832                 if (!unmap_ctx)
833                         return -ENOMEM;
834
835                 userfaultfd_ctx_get(ctx);
836                 WRITE_ONCE(ctx->mmap_changing, true);
837                 unmap_ctx->ctx = ctx;
838                 unmap_ctx->start = start;
839                 unmap_ctx->end = end;
840                 list_add_tail(&unmap_ctx->list, unmaps);
841         }
842
843         return 0;
844 }
845
846 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
847 {
848         struct userfaultfd_unmap_ctx *ctx, *n;
849         struct userfaultfd_wait_queue ewq;
850
851         list_for_each_entry_safe(ctx, n, uf, list) {
852                 msg_init(&ewq.msg);
853
854                 ewq.msg.event = UFFD_EVENT_UNMAP;
855                 ewq.msg.arg.remove.start = ctx->start;
856                 ewq.msg.arg.remove.end = ctx->end;
857
858                 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
859
860                 list_del(&ctx->list);
861                 kfree(ctx);
862         }
863 }
864
865 static int userfaultfd_release(struct inode *inode, struct file *file)
866 {
867         struct userfaultfd_ctx *ctx = file->private_data;
868         struct mm_struct *mm = ctx->mm;
869         struct vm_area_struct *vma, *prev;
870         /* len == 0 means wake all */
871         struct userfaultfd_wake_range range = { .len = 0, };
872         unsigned long new_flags;
873
874         WRITE_ONCE(ctx->released, true);
875
876         if (!mmget_not_zero(mm))
877                 goto wakeup;
878
879         /*
880          * Flush page faults out of all CPUs. NOTE: all page faults
881          * must be retried without returning VM_FAULT_SIGBUS if
882          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
883          * changes while handle_userfault released the mmap_sem. So
884          * it's critical that released is set to true (above), before
885          * taking the mmap_sem for writing.
886          */
887         down_write(&mm->mmap_sem);
888         if (!mmget_still_valid(mm))
889                 goto skip_mm;
890         prev = NULL;
891         for (vma = mm->mmap; vma; vma = vma->vm_next) {
892                 cond_resched();
893                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
894                        !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
895                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
896                         prev = vma;
897                         continue;
898                 }
899                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
900                 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
901                                  new_flags, vma->anon_vma,
902                                  vma->vm_file, vma->vm_pgoff,
903                                  vma_policy(vma),
904                                  NULL_VM_UFFD_CTX);
905                 if (prev)
906                         vma = prev;
907                 else
908                         prev = vma;
909                 vma->vm_flags = new_flags;
910                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
911         }
912 skip_mm:
913         up_write(&mm->mmap_sem);
914         mmput(mm);
915 wakeup:
916         /*
917          * After no new page faults can wait on this fault_*wqh, flush
918          * the last page faults that may have been already waiting on
919          * the fault_*wqh.
920          */
921         spin_lock(&ctx->fault_pending_wqh.lock);
922         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
923         __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
924         spin_unlock(&ctx->fault_pending_wqh.lock);
925
926         /* Flush pending events that may still wait on event_wqh */
927         wake_up_all(&ctx->event_wqh);
928
929         wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
930         userfaultfd_ctx_put(ctx);
931         return 0;
932 }
933
934 /* fault_pending_wqh.lock must be hold by the caller */
935 static inline struct userfaultfd_wait_queue *find_userfault_in(
936                 wait_queue_head_t *wqh)
937 {
938         wait_queue_entry_t *wq;
939         struct userfaultfd_wait_queue *uwq;
940
941         lockdep_assert_held(&wqh->lock);
942
943         uwq = NULL;
944         if (!waitqueue_active(wqh))
945                 goto out;
946         /* walk in reverse to provide FIFO behavior to read userfaults */
947         wq = list_last_entry(&wqh->head, typeof(*wq), entry);
948         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
949 out:
950         return uwq;
951 }
952
953 static inline struct userfaultfd_wait_queue *find_userfault(
954                 struct userfaultfd_ctx *ctx)
955 {
956         return find_userfault_in(&ctx->fault_pending_wqh);
957 }
958
959 static inline struct userfaultfd_wait_queue *find_userfault_evt(
960                 struct userfaultfd_ctx *ctx)
961 {
962         return find_userfault_in(&ctx->event_wqh);
963 }
964
965 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
966 {
967         struct userfaultfd_ctx *ctx = file->private_data;
968         __poll_t ret;
969
970         poll_wait(file, &ctx->fd_wqh, wait);
971
972         switch (ctx->state) {
973         case UFFD_STATE_WAIT_API:
974                 return EPOLLERR;
975         case UFFD_STATE_RUNNING:
976                 /*
977                  * poll() never guarantees that read won't block.
978                  * userfaults can be waken before they're read().
979                  */
980                 if (unlikely(!(file->f_flags & O_NONBLOCK)))
981                         return EPOLLERR;
982                 /*
983                  * lockless access to see if there are pending faults
984                  * __pollwait last action is the add_wait_queue but
985                  * the spin_unlock would allow the waitqueue_active to
986                  * pass above the actual list_add inside
987                  * add_wait_queue critical section. So use a full
988                  * memory barrier to serialize the list_add write of
989                  * add_wait_queue() with the waitqueue_active read
990                  * below.
991                  */
992                 ret = 0;
993                 smp_mb();
994                 if (waitqueue_active(&ctx->fault_pending_wqh))
995                         ret = EPOLLIN;
996                 else if (waitqueue_active(&ctx->event_wqh))
997                         ret = EPOLLIN;
998
999                 return ret;
1000         default:
1001                 WARN_ON_ONCE(1);
1002                 return EPOLLERR;
1003         }
1004 }
1005
1006 static const struct file_operations userfaultfd_fops;
1007
1008 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
1009                                   struct userfaultfd_ctx *new,
1010                                   struct uffd_msg *msg)
1011 {
1012         int fd;
1013
1014         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
1015                               O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
1016         if (fd < 0)
1017                 return fd;
1018
1019         msg->arg.reserved.reserved1 = 0;
1020         msg->arg.fork.ufd = fd;
1021         return 0;
1022 }
1023
1024 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1025                                     struct uffd_msg *msg)
1026 {
1027         ssize_t ret;
1028         DECLARE_WAITQUEUE(wait, current);
1029         struct userfaultfd_wait_queue *uwq;
1030         /*
1031          * Handling fork event requires sleeping operations, so
1032          * we drop the event_wqh lock, then do these ops, then
1033          * lock it back and wake up the waiter. While the lock is
1034          * dropped the ewq may go away so we keep track of it
1035          * carefully.
1036          */
1037         LIST_HEAD(fork_event);
1038         struct userfaultfd_ctx *fork_nctx = NULL;
1039
1040         /* always take the fd_wqh lock before the fault_pending_wqh lock */
1041         spin_lock_irq(&ctx->fd_wqh.lock);
1042         __add_wait_queue(&ctx->fd_wqh, &wait);
1043         for (;;) {
1044                 set_current_state(TASK_INTERRUPTIBLE);
1045                 spin_lock(&ctx->fault_pending_wqh.lock);
1046                 uwq = find_userfault(ctx);
1047                 if (uwq) {
1048                         /*
1049                          * Use a seqcount to repeat the lockless check
1050                          * in wake_userfault() to avoid missing
1051                          * wakeups because during the refile both
1052                          * waitqueue could become empty if this is the
1053                          * only userfault.
1054                          */
1055                         write_seqcount_begin(&ctx->refile_seq);
1056
1057                         /*
1058                          * The fault_pending_wqh.lock prevents the uwq
1059                          * to disappear from under us.
1060                          *
1061                          * Refile this userfault from
1062                          * fault_pending_wqh to fault_wqh, it's not
1063                          * pending anymore after we read it.
1064                          *
1065                          * Use list_del() by hand (as
1066                          * userfaultfd_wake_function also uses
1067                          * list_del_init() by hand) to be sure nobody
1068                          * changes __remove_wait_queue() to use
1069                          * list_del_init() in turn breaking the
1070                          * !list_empty_careful() check in
1071                          * handle_userfault(). The uwq->wq.head list
1072                          * must never be empty at any time during the
1073                          * refile, or the waitqueue could disappear
1074                          * from under us. The "wait_queue_head_t"
1075                          * parameter of __remove_wait_queue() is unused
1076                          * anyway.
1077                          */
1078                         list_del(&uwq->wq.entry);
1079                         add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1080
1081                         write_seqcount_end(&ctx->refile_seq);
1082
1083                         /* careful to always initialize msg if ret == 0 */
1084                         *msg = uwq->msg;
1085                         spin_unlock(&ctx->fault_pending_wqh.lock);
1086                         ret = 0;
1087                         break;
1088                 }
1089                 spin_unlock(&ctx->fault_pending_wqh.lock);
1090
1091                 spin_lock(&ctx->event_wqh.lock);
1092                 uwq = find_userfault_evt(ctx);
1093                 if (uwq) {
1094                         *msg = uwq->msg;
1095
1096                         if (uwq->msg.event == UFFD_EVENT_FORK) {
1097                                 fork_nctx = (struct userfaultfd_ctx *)
1098                                         (unsigned long)
1099                                         uwq->msg.arg.reserved.reserved1;
1100                                 list_move(&uwq->wq.entry, &fork_event);
1101                                 /*
1102                                  * fork_nctx can be freed as soon as
1103                                  * we drop the lock, unless we take a
1104                                  * reference on it.
1105                                  */
1106                                 userfaultfd_ctx_get(fork_nctx);
1107                                 spin_unlock(&ctx->event_wqh.lock);
1108                                 ret = 0;
1109                                 break;
1110                         }
1111
1112                         userfaultfd_event_complete(ctx, uwq);
1113                         spin_unlock(&ctx->event_wqh.lock);
1114                         ret = 0;
1115                         break;
1116                 }
1117                 spin_unlock(&ctx->event_wqh.lock);
1118
1119                 if (signal_pending(current)) {
1120                         ret = -ERESTARTSYS;
1121                         break;
1122                 }
1123                 if (no_wait) {
1124                         ret = -EAGAIN;
1125                         break;
1126                 }
1127                 spin_unlock_irq(&ctx->fd_wqh.lock);
1128                 schedule();
1129                 spin_lock_irq(&ctx->fd_wqh.lock);
1130         }
1131         __remove_wait_queue(&ctx->fd_wqh, &wait);
1132         __set_current_state(TASK_RUNNING);
1133         spin_unlock_irq(&ctx->fd_wqh.lock);
1134
1135         if (!ret && msg->event == UFFD_EVENT_FORK) {
1136                 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1137                 spin_lock(&ctx->event_wqh.lock);
1138                 if (!list_empty(&fork_event)) {
1139                         /*
1140                          * The fork thread didn't abort, so we can
1141                          * drop the temporary refcount.
1142                          */
1143                         userfaultfd_ctx_put(fork_nctx);
1144
1145                         uwq = list_first_entry(&fork_event,
1146                                                typeof(*uwq),
1147                                                wq.entry);
1148                         /*
1149                          * If fork_event list wasn't empty and in turn
1150                          * the event wasn't already released by fork
1151                          * (the event is allocated on fork kernel
1152                          * stack), put the event back to its place in
1153                          * the event_wq. fork_event head will be freed
1154                          * as soon as we return so the event cannot
1155                          * stay queued there no matter the current
1156                          * "ret" value.
1157                          */
1158                         list_del(&uwq->wq.entry);
1159                         __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1160
1161                         /*
1162                          * Leave the event in the waitqueue and report
1163                          * error to userland if we failed to resolve
1164                          * the userfault fork.
1165                          */
1166                         if (likely(!ret))
1167                                 userfaultfd_event_complete(ctx, uwq);
1168                 } else {
1169                         /*
1170                          * Here the fork thread aborted and the
1171                          * refcount from the fork thread on fork_nctx
1172                          * has already been released. We still hold
1173                          * the reference we took before releasing the
1174                          * lock above. If resolve_userfault_fork
1175                          * failed we've to drop it because the
1176                          * fork_nctx has to be freed in such case. If
1177                          * it succeeded we'll hold it because the new
1178                          * uffd references it.
1179                          */
1180                         if (ret)
1181                                 userfaultfd_ctx_put(fork_nctx);
1182                 }
1183                 spin_unlock(&ctx->event_wqh.lock);
1184         }
1185
1186         return ret;
1187 }
1188
1189 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1190                                 size_t count, loff_t *ppos)
1191 {
1192         struct userfaultfd_ctx *ctx = file->private_data;
1193         ssize_t _ret, ret = 0;
1194         struct uffd_msg msg;
1195         int no_wait = file->f_flags & O_NONBLOCK;
1196
1197         if (ctx->state == UFFD_STATE_WAIT_API)
1198                 return -EINVAL;
1199
1200         for (;;) {
1201                 if (count < sizeof(msg))
1202                         return ret ? ret : -EINVAL;
1203                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1204                 if (_ret < 0)
1205                         return ret ? ret : _ret;
1206                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1207                         return ret ? ret : -EFAULT;
1208                 ret += sizeof(msg);
1209                 buf += sizeof(msg);
1210                 count -= sizeof(msg);
1211                 /*
1212                  * Allow to read more than one fault at time but only
1213                  * block if waiting for the very first one.
1214                  */
1215                 no_wait = O_NONBLOCK;
1216         }
1217 }
1218
1219 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1220                              struct userfaultfd_wake_range *range)
1221 {
1222         spin_lock(&ctx->fault_pending_wqh.lock);
1223         /* wake all in the range and autoremove */
1224         if (waitqueue_active(&ctx->fault_pending_wqh))
1225                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1226                                      range);
1227         if (waitqueue_active(&ctx->fault_wqh))
1228                 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1229         spin_unlock(&ctx->fault_pending_wqh.lock);
1230 }
1231
1232 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1233                                            struct userfaultfd_wake_range *range)
1234 {
1235         unsigned seq;
1236         bool need_wakeup;
1237
1238         /*
1239          * To be sure waitqueue_active() is not reordered by the CPU
1240          * before the pagetable update, use an explicit SMP memory
1241          * barrier here. PT lock release or up_read(mmap_sem) still
1242          * have release semantics that can allow the
1243          * waitqueue_active() to be reordered before the pte update.
1244          */
1245         smp_mb();
1246
1247         /*
1248          * Use waitqueue_active because it's very frequent to
1249          * change the address space atomically even if there are no
1250          * userfaults yet. So we take the spinlock only when we're
1251          * sure we've userfaults to wake.
1252          */
1253         do {
1254                 seq = read_seqcount_begin(&ctx->refile_seq);
1255                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1256                         waitqueue_active(&ctx->fault_wqh);
1257                 cond_resched();
1258         } while (read_seqcount_retry(&ctx->refile_seq, seq));
1259         if (need_wakeup)
1260                 __wake_userfault(ctx, range);
1261 }
1262
1263 static __always_inline int validate_range(struct mm_struct *mm,
1264                                           __u64 start, __u64 len)
1265 {
1266         __u64 task_size = mm->task_size;
1267
1268         if (start & ~PAGE_MASK)
1269                 return -EINVAL;
1270         if (len & ~PAGE_MASK)
1271                 return -EINVAL;
1272         if (!len)
1273                 return -EINVAL;
1274         if (start < mmap_min_addr)
1275                 return -EINVAL;
1276         if (start >= task_size)
1277                 return -EINVAL;
1278         if (len > task_size - start)
1279                 return -EINVAL;
1280         return 0;
1281 }
1282
1283 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1284 {
1285         return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1286                 vma_is_shmem(vma);
1287 }
1288
1289 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1290                                 unsigned long arg)
1291 {
1292         struct mm_struct *mm = ctx->mm;
1293         struct vm_area_struct *vma, *prev, *cur;
1294         int ret;
1295         struct uffdio_register uffdio_register;
1296         struct uffdio_register __user *user_uffdio_register;
1297         unsigned long vm_flags, new_flags;
1298         bool found;
1299         bool basic_ioctls;
1300         unsigned long start, end, vma_end;
1301
1302         user_uffdio_register = (struct uffdio_register __user *) arg;
1303
1304         ret = -EFAULT;
1305         if (copy_from_user(&uffdio_register, user_uffdio_register,
1306                            sizeof(uffdio_register)-sizeof(__u64)))
1307                 goto out;
1308
1309         ret = -EINVAL;
1310         if (!uffdio_register.mode)
1311                 goto out;
1312         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1313                                      UFFDIO_REGISTER_MODE_WP))
1314                 goto out;
1315         vm_flags = 0;
1316         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1317                 vm_flags |= VM_UFFD_MISSING;
1318         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1319                 vm_flags |= VM_UFFD_WP;
1320                 /*
1321                  * FIXME: remove the below error constraint by
1322                  * implementing the wprotect tracking mode.
1323                  */
1324                 ret = -EINVAL;
1325                 goto out;
1326         }
1327
1328         ret = validate_range(mm, uffdio_register.range.start,
1329                              uffdio_register.range.len);
1330         if (ret)
1331                 goto out;
1332
1333         start = uffdio_register.range.start;
1334         end = start + uffdio_register.range.len;
1335
1336         ret = -ENOMEM;
1337         if (!mmget_not_zero(mm))
1338                 goto out;
1339
1340         down_write(&mm->mmap_sem);
1341         if (!mmget_still_valid(mm))
1342                 goto out_unlock;
1343         vma = find_vma_prev(mm, start, &prev);
1344         if (!vma)
1345                 goto out_unlock;
1346
1347         /* check that there's at least one vma in the range */
1348         ret = -EINVAL;
1349         if (vma->vm_start >= end)
1350                 goto out_unlock;
1351
1352         /*
1353          * If the first vma contains huge pages, make sure start address
1354          * is aligned to huge page size.
1355          */
1356         if (is_vm_hugetlb_page(vma)) {
1357                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1358
1359                 if (start & (vma_hpagesize - 1))
1360                         goto out_unlock;
1361         }
1362
1363         /*
1364          * Search for not compatible vmas.
1365          */
1366         found = false;
1367         basic_ioctls = false;
1368         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1369                 cond_resched();
1370
1371                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1372                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1373
1374                 /* check not compatible vmas */
1375                 ret = -EINVAL;
1376                 if (!vma_can_userfault(cur))
1377                         goto out_unlock;
1378
1379                 /*
1380                  * UFFDIO_COPY will fill file holes even without
1381                  * PROT_WRITE. This check enforces that if this is a
1382                  * MAP_SHARED, the process has write permission to the backing
1383                  * file. If VM_MAYWRITE is set it also enforces that on a
1384                  * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1385                  * F_WRITE_SEAL can be taken until the vma is destroyed.
1386                  */
1387                 ret = -EPERM;
1388                 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1389                         goto out_unlock;
1390
1391                 /*
1392                  * If this vma contains ending address, and huge pages
1393                  * check alignment.
1394                  */
1395                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1396                     end > cur->vm_start) {
1397                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1398
1399                         ret = -EINVAL;
1400
1401                         if (end & (vma_hpagesize - 1))
1402                                 goto out_unlock;
1403                 }
1404
1405                 /*
1406                  * Check that this vma isn't already owned by a
1407                  * different userfaultfd. We can't allow more than one
1408                  * userfaultfd to own a single vma simultaneously or we
1409                  * wouldn't know which one to deliver the userfaults to.
1410                  */
1411                 ret = -EBUSY;
1412                 if (cur->vm_userfaultfd_ctx.ctx &&
1413                     cur->vm_userfaultfd_ctx.ctx != ctx)
1414                         goto out_unlock;
1415
1416                 /*
1417                  * Note vmas containing huge pages
1418                  */
1419                 if (is_vm_hugetlb_page(cur))
1420                         basic_ioctls = true;
1421
1422                 found = true;
1423         }
1424         BUG_ON(!found);
1425
1426         if (vma->vm_start < start)
1427                 prev = vma;
1428
1429         ret = 0;
1430         do {
1431                 cond_resched();
1432
1433                 BUG_ON(!vma_can_userfault(vma));
1434                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1435                        vma->vm_userfaultfd_ctx.ctx != ctx);
1436                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1437
1438                 /*
1439                  * Nothing to do: this vma is already registered into this
1440                  * userfaultfd and with the right tracking mode too.
1441                  */
1442                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1443                     (vma->vm_flags & vm_flags) == vm_flags)
1444                         goto skip;
1445
1446                 if (vma->vm_start > start)
1447                         start = vma->vm_start;
1448                 vma_end = min(end, vma->vm_end);
1449
1450                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1451                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1452                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1453                                  vma_policy(vma),
1454                                  ((struct vm_userfaultfd_ctx){ ctx }));
1455                 if (prev) {
1456                         vma = prev;
1457                         goto next;
1458                 }
1459                 if (vma->vm_start < start) {
1460                         ret = split_vma(mm, vma, start, 1);
1461                         if (ret)
1462                                 break;
1463                 }
1464                 if (vma->vm_end > end) {
1465                         ret = split_vma(mm, vma, end, 0);
1466                         if (ret)
1467                                 break;
1468                 }
1469         next:
1470                 /*
1471                  * In the vma_merge() successful mprotect-like case 8:
1472                  * the next vma was merged into the current one and
1473                  * the current one has not been updated yet.
1474                  */
1475                 vma->vm_flags = new_flags;
1476                 vma->vm_userfaultfd_ctx.ctx = ctx;
1477
1478         skip:
1479                 prev = vma;
1480                 start = vma->vm_end;
1481                 vma = vma->vm_next;
1482         } while (vma && vma->vm_start < end);
1483 out_unlock:
1484         up_write(&mm->mmap_sem);
1485         mmput(mm);
1486         if (!ret) {
1487                 /*
1488                  * Now that we scanned all vmas we can already tell
1489                  * userland which ioctls methods are guaranteed to
1490                  * succeed on this range.
1491                  */
1492                 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1493                              UFFD_API_RANGE_IOCTLS,
1494                              &user_uffdio_register->ioctls))
1495                         ret = -EFAULT;
1496         }
1497 out:
1498         return ret;
1499 }
1500
1501 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1502                                   unsigned long arg)
1503 {
1504         struct mm_struct *mm = ctx->mm;
1505         struct vm_area_struct *vma, *prev, *cur;
1506         int ret;
1507         struct uffdio_range uffdio_unregister;
1508         unsigned long new_flags;
1509         bool found;
1510         unsigned long start, end, vma_end;
1511         const void __user *buf = (void __user *)arg;
1512
1513         ret = -EFAULT;
1514         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1515                 goto out;
1516
1517         ret = validate_range(mm, uffdio_unregister.start,
1518                              uffdio_unregister.len);
1519         if (ret)
1520                 goto out;
1521
1522         start = uffdio_unregister.start;
1523         end = start + uffdio_unregister.len;
1524
1525         ret = -ENOMEM;
1526         if (!mmget_not_zero(mm))
1527                 goto out;
1528
1529         down_write(&mm->mmap_sem);
1530         if (!mmget_still_valid(mm))
1531                 goto out_unlock;
1532         vma = find_vma_prev(mm, start, &prev);
1533         if (!vma)
1534                 goto out_unlock;
1535
1536         /* check that there's at least one vma in the range */
1537         ret = -EINVAL;
1538         if (vma->vm_start >= end)
1539                 goto out_unlock;
1540
1541         /*
1542          * If the first vma contains huge pages, make sure start address
1543          * is aligned to huge page size.
1544          */
1545         if (is_vm_hugetlb_page(vma)) {
1546                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1547
1548                 if (start & (vma_hpagesize - 1))
1549                         goto out_unlock;
1550         }
1551
1552         /*
1553          * Search for not compatible vmas.
1554          */
1555         found = false;
1556         ret = -EINVAL;
1557         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1558                 cond_resched();
1559
1560                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1561                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1562
1563                 /*
1564                  * Check not compatible vmas, not strictly required
1565                  * here as not compatible vmas cannot have an
1566                  * userfaultfd_ctx registered on them, but this
1567                  * provides for more strict behavior to notice
1568                  * unregistration errors.
1569                  */
1570                 if (!vma_can_userfault(cur))
1571                         goto out_unlock;
1572
1573                 found = true;
1574         }
1575         BUG_ON(!found);
1576
1577         if (vma->vm_start < start)
1578                 prev = vma;
1579
1580         ret = 0;
1581         do {
1582                 cond_resched();
1583
1584                 BUG_ON(!vma_can_userfault(vma));
1585
1586                 /*
1587                  * Nothing to do: this vma is already registered into this
1588                  * userfaultfd and with the right tracking mode too.
1589                  */
1590                 if (!vma->vm_userfaultfd_ctx.ctx)
1591                         goto skip;
1592
1593                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1594
1595                 if (vma->vm_start > start)
1596                         start = vma->vm_start;
1597                 vma_end = min(end, vma->vm_end);
1598
1599                 if (userfaultfd_missing(vma)) {
1600                         /*
1601                          * Wake any concurrent pending userfault while
1602                          * we unregister, so they will not hang
1603                          * permanently and it avoids userland to call
1604                          * UFFDIO_WAKE explicitly.
1605                          */
1606                         struct userfaultfd_wake_range range;
1607                         range.start = start;
1608                         range.len = vma_end - start;
1609                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1610                 }
1611
1612                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1613                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1614                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1615                                  vma_policy(vma),
1616                                  NULL_VM_UFFD_CTX);
1617                 if (prev) {
1618                         vma = prev;
1619                         goto next;
1620                 }
1621                 if (vma->vm_start < start) {
1622                         ret = split_vma(mm, vma, start, 1);
1623                         if (ret)
1624                                 break;
1625                 }
1626                 if (vma->vm_end > end) {
1627                         ret = split_vma(mm, vma, end, 0);
1628                         if (ret)
1629                                 break;
1630                 }
1631         next:
1632                 /*
1633                  * In the vma_merge() successful mprotect-like case 8:
1634                  * the next vma was merged into the current one and
1635                  * the current one has not been updated yet.
1636                  */
1637                 vma->vm_flags = new_flags;
1638                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1639
1640         skip:
1641                 prev = vma;
1642                 start = vma->vm_end;
1643                 vma = vma->vm_next;
1644         } while (vma && vma->vm_start < end);
1645 out_unlock:
1646         up_write(&mm->mmap_sem);
1647         mmput(mm);
1648 out:
1649         return ret;
1650 }
1651
1652 /*
1653  * userfaultfd_wake may be used in combination with the
1654  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1655  */
1656 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1657                             unsigned long arg)
1658 {
1659         int ret;
1660         struct uffdio_range uffdio_wake;
1661         struct userfaultfd_wake_range range;
1662         const void __user *buf = (void __user *)arg;
1663
1664         ret = -EFAULT;
1665         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1666                 goto out;
1667
1668         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1669         if (ret)
1670                 goto out;
1671
1672         range.start = uffdio_wake.start;
1673         range.len = uffdio_wake.len;
1674
1675         /*
1676          * len == 0 means wake all and we don't want to wake all here,
1677          * so check it again to be sure.
1678          */
1679         VM_BUG_ON(!range.len);
1680
1681         wake_userfault(ctx, &range);
1682         ret = 0;
1683
1684 out:
1685         return ret;
1686 }
1687
1688 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1689                             unsigned long arg)
1690 {
1691         __s64 ret;
1692         struct uffdio_copy uffdio_copy;
1693         struct uffdio_copy __user *user_uffdio_copy;
1694         struct userfaultfd_wake_range range;
1695
1696         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1697
1698         ret = -EAGAIN;
1699         if (READ_ONCE(ctx->mmap_changing))
1700                 goto out;
1701
1702         ret = -EFAULT;
1703         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1704                            /* don't copy "copy" last field */
1705                            sizeof(uffdio_copy)-sizeof(__s64)))
1706                 goto out;
1707
1708         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1709         if (ret)
1710                 goto out;
1711         /*
1712          * double check for wraparound just in case. copy_from_user()
1713          * will later check uffdio_copy.src + uffdio_copy.len to fit
1714          * in the userland range.
1715          */
1716         ret = -EINVAL;
1717         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1718                 goto out;
1719         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1720                 goto out;
1721         if (mmget_not_zero(ctx->mm)) {
1722                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1723                                    uffdio_copy.len, &ctx->mmap_changing);
1724                 mmput(ctx->mm);
1725         } else {
1726                 return -ESRCH;
1727         }
1728         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1729                 return -EFAULT;
1730         if (ret < 0)
1731                 goto out;
1732         BUG_ON(!ret);
1733         /* len == 0 would wake all */
1734         range.len = ret;
1735         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1736                 range.start = uffdio_copy.dst;
1737                 wake_userfault(ctx, &range);
1738         }
1739         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1740 out:
1741         return ret;
1742 }
1743
1744 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1745                                 unsigned long arg)
1746 {
1747         __s64 ret;
1748         struct uffdio_zeropage uffdio_zeropage;
1749         struct uffdio_zeropage __user *user_uffdio_zeropage;
1750         struct userfaultfd_wake_range range;
1751
1752         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1753
1754         ret = -EAGAIN;
1755         if (READ_ONCE(ctx->mmap_changing))
1756                 goto out;
1757
1758         ret = -EFAULT;
1759         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1760                            /* don't copy "zeropage" last field */
1761                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1762                 goto out;
1763
1764         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1765                              uffdio_zeropage.range.len);
1766         if (ret)
1767                 goto out;
1768         ret = -EINVAL;
1769         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1770                 goto out;
1771
1772         if (mmget_not_zero(ctx->mm)) {
1773                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1774                                      uffdio_zeropage.range.len,
1775                                      &ctx->mmap_changing);
1776                 mmput(ctx->mm);
1777         } else {
1778                 return -ESRCH;
1779         }
1780         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1781                 return -EFAULT;
1782         if (ret < 0)
1783                 goto out;
1784         /* len == 0 would wake all */
1785         BUG_ON(!ret);
1786         range.len = ret;
1787         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1788                 range.start = uffdio_zeropage.range.start;
1789                 wake_userfault(ctx, &range);
1790         }
1791         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1792 out:
1793         return ret;
1794 }
1795
1796 static inline unsigned int uffd_ctx_features(__u64 user_features)
1797 {
1798         /*
1799          * For the current set of features the bits just coincide
1800          */
1801         return (unsigned int)user_features;
1802 }
1803
1804 /*
1805  * userland asks for a certain API version and we return which bits
1806  * and ioctl commands are implemented in this kernel for such API
1807  * version or -EINVAL if unknown.
1808  */
1809 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1810                            unsigned long arg)
1811 {
1812         struct uffdio_api uffdio_api;
1813         void __user *buf = (void __user *)arg;
1814         int ret;
1815         __u64 features;
1816
1817         ret = -EINVAL;
1818         if (ctx->state != UFFD_STATE_WAIT_API)
1819                 goto out;
1820         ret = -EFAULT;
1821         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1822                 goto out;
1823         features = uffdio_api.features;
1824         if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
1825                 memset(&uffdio_api, 0, sizeof(uffdio_api));
1826                 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1827                         goto out;
1828                 ret = -EINVAL;
1829                 goto out;
1830         }
1831         /* report all available features and ioctls to userland */
1832         uffdio_api.features = UFFD_API_FEATURES;
1833         uffdio_api.ioctls = UFFD_API_IOCTLS;
1834         ret = -EFAULT;
1835         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1836                 goto out;
1837         ctx->state = UFFD_STATE_RUNNING;
1838         /* only enable the requested features for this uffd context */
1839         ctx->features = uffd_ctx_features(features);
1840         ret = 0;
1841 out:
1842         return ret;
1843 }
1844
1845 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1846                               unsigned long arg)
1847 {
1848         int ret = -EINVAL;
1849         struct userfaultfd_ctx *ctx = file->private_data;
1850
1851         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1852                 return -EINVAL;
1853
1854         switch(cmd) {
1855         case UFFDIO_API:
1856                 ret = userfaultfd_api(ctx, arg);
1857                 break;
1858         case UFFDIO_REGISTER:
1859                 ret = userfaultfd_register(ctx, arg);
1860                 break;
1861         case UFFDIO_UNREGISTER:
1862                 ret = userfaultfd_unregister(ctx, arg);
1863                 break;
1864         case UFFDIO_WAKE:
1865                 ret = userfaultfd_wake(ctx, arg);
1866                 break;
1867         case UFFDIO_COPY:
1868                 ret = userfaultfd_copy(ctx, arg);
1869                 break;
1870         case UFFDIO_ZEROPAGE:
1871                 ret = userfaultfd_zeropage(ctx, arg);
1872                 break;
1873         }
1874         return ret;
1875 }
1876
1877 #ifdef CONFIG_PROC_FS
1878 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1879 {
1880         struct userfaultfd_ctx *ctx = f->private_data;
1881         wait_queue_entry_t *wq;
1882         unsigned long pending = 0, total = 0;
1883
1884         spin_lock(&ctx->fault_pending_wqh.lock);
1885         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1886                 pending++;
1887                 total++;
1888         }
1889         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1890                 total++;
1891         }
1892         spin_unlock(&ctx->fault_pending_wqh.lock);
1893
1894         /*
1895          * If more protocols will be added, there will be all shown
1896          * separated by a space. Like this:
1897          *      protocols: aa:... bb:...
1898          */
1899         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1900                    pending, total, UFFD_API, ctx->features,
1901                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1902 }
1903 #endif
1904
1905 static const struct file_operations userfaultfd_fops = {
1906 #ifdef CONFIG_PROC_FS
1907         .show_fdinfo    = userfaultfd_show_fdinfo,
1908 #endif
1909         .release        = userfaultfd_release,
1910         .poll           = userfaultfd_poll,
1911         .read           = userfaultfd_read,
1912         .unlocked_ioctl = userfaultfd_ioctl,
1913         .compat_ioctl   = userfaultfd_ioctl,
1914         .llseek         = noop_llseek,
1915 };
1916
1917 static void init_once_userfaultfd_ctx(void *mem)
1918 {
1919         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1920
1921         init_waitqueue_head(&ctx->fault_pending_wqh);
1922         init_waitqueue_head(&ctx->fault_wqh);
1923         init_waitqueue_head(&ctx->event_wqh);
1924         init_waitqueue_head(&ctx->fd_wqh);
1925         seqcount_init(&ctx->refile_seq);
1926 }
1927
1928 SYSCALL_DEFINE1(userfaultfd, int, flags)
1929 {
1930         struct userfaultfd_ctx *ctx;
1931         int fd;
1932
1933         BUG_ON(!current->mm);
1934
1935         /* Check the UFFD_* constants for consistency.  */
1936         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1937         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1938
1939         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1940                 return -EINVAL;
1941
1942         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1943         if (!ctx)
1944                 return -ENOMEM;
1945
1946         refcount_set(&ctx->refcount, 1);
1947         ctx->flags = flags;
1948         ctx->features = 0;
1949         ctx->state = UFFD_STATE_WAIT_API;
1950         ctx->released = false;
1951         ctx->mmap_changing = false;
1952         ctx->mm = current->mm;
1953         /* prevent the mm struct to be freed */
1954         mmgrab(ctx->mm);
1955
1956         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
1957                               O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1958         if (fd < 0) {
1959                 mmdrop(ctx->mm);
1960                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1961         }
1962         return fd;
1963 }
1964
1965 static int __init userfaultfd_init(void)
1966 {
1967         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1968                                                 sizeof(struct userfaultfd_ctx),
1969                                                 0,
1970                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1971                                                 init_once_userfaultfd_ctx);
1972         return 0;
1973 }
1974 __initcall(userfaultfd_init);