7a85e609fc276f28dd80c8dc481e383094d1dfe9
[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         atomic_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         if (!atomic_inc_not_zero(&ctx->refcount))
144                 BUG();
145 }
146
147 /**
148  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
149  * context.
150  * @ctx: [in] Pointer to userfaultfd context.
151  *
152  * The userfaultfd context reference must have been previously acquired either
153  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
154  */
155 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
156 {
157         if (atomic_dec_and_test(&ctx->refcount)) {
158                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
159                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
160                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
161                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
162                 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
163                 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
164                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
165                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
166                 mmdrop(ctx->mm);
167                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
168         }
169 }
170
171 static inline void msg_init(struct uffd_msg *msg)
172 {
173         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
174         /*
175          * Must use memset to zero out the paddings or kernel data is
176          * leaked to userland.
177          */
178         memset(msg, 0, sizeof(struct uffd_msg));
179 }
180
181 static inline struct uffd_msg userfault_msg(unsigned long address,
182                                             unsigned int flags,
183                                             unsigned long reason,
184                                             unsigned int features)
185 {
186         struct uffd_msg msg;
187         msg_init(&msg);
188         msg.event = UFFD_EVENT_PAGEFAULT;
189         msg.arg.pagefault.address = address;
190         if (flags & FAULT_FLAG_WRITE)
191                 /*
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
196                  * a write fault.
197                  */
198                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
199         if (reason & VM_UFFD_WP)
200                 /*
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.
206                  */
207                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
208         if (features & UFFD_FEATURE_THREAD_ID)
209                 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
210         return msg;
211 }
212
213 #ifdef CONFIG_HUGETLB_PAGE
214 /*
215  * Same functionality as userfaultfd_must_wait below with modifications for
216  * hugepmd ranges.
217  */
218 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
219                                          struct vm_area_struct *vma,
220                                          unsigned long address,
221                                          unsigned long flags,
222                                          unsigned long reason)
223 {
224         struct mm_struct *mm = ctx->mm;
225         pte_t *ptep, pte;
226         bool ret = true;
227
228         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
229
230         ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));
231
232         if (!ptep)
233                 goto out;
234
235         ret = false;
236         pte = huge_ptep_get(ptep);
237
238         /*
239          * Lockless access: we're in a wait_event so it's ok if it
240          * changes under us.
241          */
242         if (huge_pte_none(pte))
243                 ret = true;
244         if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
245                 ret = true;
246 out:
247         return ret;
248 }
249 #else
250 static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
251                                          struct vm_area_struct *vma,
252                                          unsigned long address,
253                                          unsigned long flags,
254                                          unsigned long reason)
255 {
256         return false;   /* should never get here */
257 }
258 #endif /* CONFIG_HUGETLB_PAGE */
259
260 /*
261  * Verify the pagetables are still not ok after having reigstered into
262  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
263  * userfault that has already been resolved, if userfaultfd_read and
264  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
265  * threads.
266  */
267 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
268                                          unsigned long address,
269                                          unsigned long flags,
270                                          unsigned long reason)
271 {
272         struct mm_struct *mm = ctx->mm;
273         pgd_t *pgd;
274         p4d_t *p4d;
275         pud_t *pud;
276         pmd_t *pmd, _pmd;
277         pte_t *pte;
278         bool ret = true;
279
280         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
281
282         pgd = pgd_offset(mm, address);
283         if (!pgd_present(*pgd))
284                 goto out;
285         p4d = p4d_offset(pgd, address);
286         if (!p4d_present(*p4d))
287                 goto out;
288         pud = pud_offset(p4d, address);
289         if (!pud_present(*pud))
290                 goto out;
291         pmd = pmd_offset(pud, address);
292         /*
293          * READ_ONCE must function as a barrier with narrower scope
294          * and it must be equivalent to:
295          *      _pmd = *pmd; barrier();
296          *
297          * This is to deal with the instability (as in
298          * pmd_trans_unstable) of the pmd.
299          */
300         _pmd = READ_ONCE(*pmd);
301         if (pmd_none(_pmd))
302                 goto out;
303
304         ret = false;
305         if (!pmd_present(_pmd))
306                 goto out;
307
308         if (pmd_trans_huge(_pmd))
309                 goto out;
310
311         /*
312          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
313          * and use the standard pte_offset_map() instead of parsing _pmd.
314          */
315         pte = pte_offset_map(pmd, address);
316         /*
317          * Lockless access: we're in a wait_event so it's ok if it
318          * changes under us.
319          */
320         if (pte_none(*pte))
321                 ret = true;
322         pte_unmap(pte);
323
324 out:
325         return ret;
326 }
327
328 /*
329  * The locking rules involved in returning VM_FAULT_RETRY depending on
330  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
331  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
332  * recommendation in __lock_page_or_retry is not an understatement.
333  *
334  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
335  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
336  * not set.
337  *
338  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
339  * set, VM_FAULT_RETRY can still be returned if and only if there are
340  * fatal_signal_pending()s, and the mmap_sem must be released before
341  * returning it.
342  */
343 vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
344 {
345         struct mm_struct *mm = vmf->vma->vm_mm;
346         struct userfaultfd_ctx *ctx;
347         struct userfaultfd_wait_queue uwq;
348         vm_fault_t ret = VM_FAULT_SIGBUS;
349         bool must_wait, return_to_userland;
350         long blocking_state;
351
352         /*
353          * We don't do userfault handling for the final child pid update.
354          *
355          * We also don't do userfault handling during
356          * coredumping. hugetlbfs has the special
357          * follow_hugetlb_page() to skip missing pages in the
358          * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
359          * the no_page_table() helper in follow_page_mask(), but the
360          * shmem_vm_ops->fault method is invoked even during
361          * coredumping without mmap_sem and it ends up here.
362          */
363         if (current->flags & (PF_EXITING|PF_DUMPCORE))
364                 goto out;
365
366         /*
367          * Coredumping runs without mmap_sem so we can only check that
368          * the mmap_sem is held, if PF_DUMPCORE was not set.
369          */
370         WARN_ON_ONCE(!rwsem_is_locked(&mm->mmap_sem));
371
372         ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
373         if (!ctx)
374                 goto out;
375
376         BUG_ON(ctx->mm != mm);
377
378         VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
379         VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
380
381         if (ctx->features & UFFD_FEATURE_SIGBUS)
382                 goto out;
383
384         /*
385          * If it's already released don't get it. This avoids to loop
386          * in __get_user_pages if userfaultfd_release waits on the
387          * caller of handle_userfault to release the mmap_sem.
388          */
389         if (unlikely(READ_ONCE(ctx->released))) {
390                 /*
391                  * Don't return VM_FAULT_SIGBUS in this case, so a non
392                  * cooperative manager can close the uffd after the
393                  * last UFFDIO_COPY, without risking to trigger an
394                  * involuntary SIGBUS if the process was starting the
395                  * userfaultfd while the userfaultfd was still armed
396                  * (but after the last UFFDIO_COPY). If the uffd
397                  * wasn't already closed when the userfault reached
398                  * this point, that would normally be solved by
399                  * userfaultfd_must_wait returning 'false'.
400                  *
401                  * If we were to return VM_FAULT_SIGBUS here, the non
402                  * cooperative manager would be instead forced to
403                  * always call UFFDIO_UNREGISTER before it can safely
404                  * close the uffd.
405                  */
406                 ret = VM_FAULT_NOPAGE;
407                 goto out;
408         }
409
410         /*
411          * Check that we can return VM_FAULT_RETRY.
412          *
413          * NOTE: it should become possible to return VM_FAULT_RETRY
414          * even if FAULT_FLAG_TRIED is set without leading to gup()
415          * -EBUSY failures, if the userfaultfd is to be extended for
416          * VM_UFFD_WP tracking and we intend to arm the userfault
417          * without first stopping userland access to the memory. For
418          * VM_UFFD_MISSING userfaults this is enough for now.
419          */
420         if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
421                 /*
422                  * Validate the invariant that nowait must allow retry
423                  * to be sure not to return SIGBUS erroneously on
424                  * nowait invocations.
425                  */
426                 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
427 #ifdef CONFIG_DEBUG_VM
428                 if (printk_ratelimit()) {
429                         printk(KERN_WARNING
430                                "FAULT_FLAG_ALLOW_RETRY missing %x\n",
431                                vmf->flags);
432                         dump_stack();
433                 }
434 #endif
435                 goto out;
436         }
437
438         /*
439          * Handle nowait, not much to do other than tell it to retry
440          * and wait.
441          */
442         ret = VM_FAULT_RETRY;
443         if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
444                 goto out;
445
446         /* take the reference before dropping the mmap_sem */
447         userfaultfd_ctx_get(ctx);
448
449         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
450         uwq.wq.private = current;
451         uwq.msg = userfault_msg(vmf->address, vmf->flags, reason,
452                         ctx->features);
453         uwq.ctx = ctx;
454         uwq.waken = false;
455
456         return_to_userland =
457                 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
458                 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
459         blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
460                          TASK_KILLABLE;
461
462         spin_lock(&ctx->fault_pending_wqh.lock);
463         /*
464          * After the __add_wait_queue the uwq is visible to userland
465          * through poll/read().
466          */
467         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
468         /*
469          * The smp_mb() after __set_current_state prevents the reads
470          * following the spin_unlock to happen before the list_add in
471          * __add_wait_queue.
472          */
473         set_current_state(blocking_state);
474         spin_unlock(&ctx->fault_pending_wqh.lock);
475
476         if (!is_vm_hugetlb_page(vmf->vma))
477                 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
478                                                   reason);
479         else
480                 must_wait = userfaultfd_huge_must_wait(ctx, vmf->vma,
481                                                        vmf->address,
482                                                        vmf->flags, reason);
483         up_read(&mm->mmap_sem);
484
485         if (likely(must_wait && !READ_ONCE(ctx->released) &&
486                    (return_to_userland ? !signal_pending(current) :
487                     !fatal_signal_pending(current)))) {
488                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
489                 schedule();
490                 ret |= VM_FAULT_MAJOR;
491
492                 /*
493                  * False wakeups can orginate even from rwsem before
494                  * up_read() however userfaults will wait either for a
495                  * targeted wakeup on the specific uwq waitqueue from
496                  * wake_userfault() or for signals or for uffd
497                  * release.
498                  */
499                 while (!READ_ONCE(uwq.waken)) {
500                         /*
501                          * This needs the full smp_store_mb()
502                          * guarantee as the state write must be
503                          * visible to other CPUs before reading
504                          * uwq.waken from other CPUs.
505                          */
506                         set_current_state(blocking_state);
507                         if (READ_ONCE(uwq.waken) ||
508                             READ_ONCE(ctx->released) ||
509                             (return_to_userland ? signal_pending(current) :
510                              fatal_signal_pending(current)))
511                                 break;
512                         schedule();
513                 }
514         }
515
516         __set_current_state(TASK_RUNNING);
517
518         if (return_to_userland) {
519                 if (signal_pending(current) &&
520                     !fatal_signal_pending(current)) {
521                         /*
522                          * If we got a SIGSTOP or SIGCONT and this is
523                          * a normal userland page fault, just let
524                          * userland return so the signal will be
525                          * handled and gdb debugging works.  The page
526                          * fault code immediately after we return from
527                          * this function is going to release the
528                          * mmap_sem and it's not depending on it
529                          * (unlike gup would if we were not to return
530                          * VM_FAULT_RETRY).
531                          *
532                          * If a fatal signal is pending we still take
533                          * the streamlined VM_FAULT_RETRY failure path
534                          * and there's no need to retake the mmap_sem
535                          * in such case.
536                          */
537                         down_read(&mm->mmap_sem);
538                         ret = VM_FAULT_NOPAGE;
539                 }
540         }
541
542         /*
543          * Here we race with the list_del; list_add in
544          * userfaultfd_ctx_read(), however because we don't ever run
545          * list_del_init() to refile across the two lists, the prev
546          * and next pointers will never point to self. list_add also
547          * would never let any of the two pointers to point to
548          * self. So list_empty_careful won't risk to see both pointers
549          * pointing to self at any time during the list refile. The
550          * only case where list_del_init() is called is the full
551          * removal in the wake function and there we don't re-list_add
552          * and it's fine not to block on the spinlock. The uwq on this
553          * kernel stack can be released after the list_del_init.
554          */
555         if (!list_empty_careful(&uwq.wq.entry)) {
556                 spin_lock(&ctx->fault_pending_wqh.lock);
557                 /*
558                  * No need of list_del_init(), the uwq on the stack
559                  * will be freed shortly anyway.
560                  */
561                 list_del(&uwq.wq.entry);
562                 spin_unlock(&ctx->fault_pending_wqh.lock);
563         }
564
565         /*
566          * ctx may go away after this if the userfault pseudo fd is
567          * already released.
568          */
569         userfaultfd_ctx_put(ctx);
570
571 out:
572         return ret;
573 }
574
575 static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
576                                               struct userfaultfd_wait_queue *ewq)
577 {
578         struct userfaultfd_ctx *release_new_ctx;
579
580         if (WARN_ON_ONCE(current->flags & PF_EXITING))
581                 goto out;
582
583         ewq->ctx = ctx;
584         init_waitqueue_entry(&ewq->wq, current);
585         release_new_ctx = NULL;
586
587         spin_lock(&ctx->event_wqh.lock);
588         /*
589          * After the __add_wait_queue the uwq is visible to userland
590          * through poll/read().
591          */
592         __add_wait_queue(&ctx->event_wqh, &ewq->wq);
593         for (;;) {
594                 set_current_state(TASK_KILLABLE);
595                 if (ewq->msg.event == 0)
596                         break;
597                 if (READ_ONCE(ctx->released) ||
598                     fatal_signal_pending(current)) {
599                         /*
600                          * &ewq->wq may be queued in fork_event, but
601                          * __remove_wait_queue ignores the head
602                          * parameter. It would be a problem if it
603                          * didn't.
604                          */
605                         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
606                         if (ewq->msg.event == UFFD_EVENT_FORK) {
607                                 struct userfaultfd_ctx *new;
608
609                                 new = (struct userfaultfd_ctx *)
610                                         (unsigned long)
611                                         ewq->msg.arg.reserved.reserved1;
612                                 release_new_ctx = new;
613                         }
614                         break;
615                 }
616
617                 spin_unlock(&ctx->event_wqh.lock);
618
619                 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
620                 schedule();
621
622                 spin_lock(&ctx->event_wqh.lock);
623         }
624         __set_current_state(TASK_RUNNING);
625         spin_unlock(&ctx->event_wqh.lock);
626
627         if (release_new_ctx) {
628                 struct vm_area_struct *vma;
629                 struct mm_struct *mm = release_new_ctx->mm;
630
631                 /* the various vma->vm_userfaultfd_ctx still points to it */
632                 down_write(&mm->mmap_sem);
633                 for (vma = mm->mmap; vma; vma = vma->vm_next)
634                         if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
635                                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
636                                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
637                         }
638                 up_write(&mm->mmap_sem);
639
640                 userfaultfd_ctx_put(release_new_ctx);
641         }
642
643         /*
644          * ctx may go away after this if the userfault pseudo fd is
645          * already released.
646          */
647 out:
648         WRITE_ONCE(ctx->mmap_changing, false);
649         userfaultfd_ctx_put(ctx);
650 }
651
652 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
653                                        struct userfaultfd_wait_queue *ewq)
654 {
655         ewq->msg.event = 0;
656         wake_up_locked(&ctx->event_wqh);
657         __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
658 }
659
660 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
661 {
662         struct userfaultfd_ctx *ctx = NULL, *octx;
663         struct userfaultfd_fork_ctx *fctx;
664
665         octx = vma->vm_userfaultfd_ctx.ctx;
666         if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
667                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
668                 vma->vm_flags &= ~(VM_UFFD_WP | VM_UFFD_MISSING);
669                 return 0;
670         }
671
672         list_for_each_entry(fctx, fcs, list)
673                 if (fctx->orig == octx) {
674                         ctx = fctx->new;
675                         break;
676                 }
677
678         if (!ctx) {
679                 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
680                 if (!fctx)
681                         return -ENOMEM;
682
683                 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
684                 if (!ctx) {
685                         kfree(fctx);
686                         return -ENOMEM;
687                 }
688
689                 atomic_set(&ctx->refcount, 1);
690                 ctx->flags = octx->flags;
691                 ctx->state = UFFD_STATE_RUNNING;
692                 ctx->features = octx->features;
693                 ctx->released = false;
694                 ctx->mmap_changing = false;
695                 ctx->mm = vma->vm_mm;
696                 mmgrab(ctx->mm);
697
698                 userfaultfd_ctx_get(octx);
699                 WRITE_ONCE(octx->mmap_changing, true);
700                 fctx->orig = octx;
701                 fctx->new = ctx;
702                 list_add_tail(&fctx->list, fcs);
703         }
704
705         vma->vm_userfaultfd_ctx.ctx = ctx;
706         return 0;
707 }
708
709 static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
710 {
711         struct userfaultfd_ctx *ctx = fctx->orig;
712         struct userfaultfd_wait_queue ewq;
713
714         msg_init(&ewq.msg);
715
716         ewq.msg.event = UFFD_EVENT_FORK;
717         ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
718
719         userfaultfd_event_wait_completion(ctx, &ewq);
720 }
721
722 void dup_userfaultfd_complete(struct list_head *fcs)
723 {
724         struct userfaultfd_fork_ctx *fctx, *n;
725
726         list_for_each_entry_safe(fctx, n, fcs, list) {
727                 dup_fctx(fctx);
728                 list_del(&fctx->list);
729                 kfree(fctx);
730         }
731 }
732
733 void mremap_userfaultfd_prep(struct vm_area_struct *vma,
734                              struct vm_userfaultfd_ctx *vm_ctx)
735 {
736         struct userfaultfd_ctx *ctx;
737
738         ctx = vma->vm_userfaultfd_ctx.ctx;
739         if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
740                 vm_ctx->ctx = ctx;
741                 userfaultfd_ctx_get(ctx);
742                 WRITE_ONCE(ctx->mmap_changing, true);
743         }
744 }
745
746 void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
747                                  unsigned long from, unsigned long to,
748                                  unsigned long len)
749 {
750         struct userfaultfd_ctx *ctx = vm_ctx->ctx;
751         struct userfaultfd_wait_queue ewq;
752
753         if (!ctx)
754                 return;
755
756         if (to & ~PAGE_MASK) {
757                 userfaultfd_ctx_put(ctx);
758                 return;
759         }
760
761         msg_init(&ewq.msg);
762
763         ewq.msg.event = UFFD_EVENT_REMAP;
764         ewq.msg.arg.remap.from = from;
765         ewq.msg.arg.remap.to = to;
766         ewq.msg.arg.remap.len = len;
767
768         userfaultfd_event_wait_completion(ctx, &ewq);
769 }
770
771 bool userfaultfd_remove(struct vm_area_struct *vma,
772                         unsigned long start, unsigned long end)
773 {
774         struct mm_struct *mm = vma->vm_mm;
775         struct userfaultfd_ctx *ctx;
776         struct userfaultfd_wait_queue ewq;
777
778         ctx = vma->vm_userfaultfd_ctx.ctx;
779         if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
780                 return true;
781
782         userfaultfd_ctx_get(ctx);
783         WRITE_ONCE(ctx->mmap_changing, true);
784         up_read(&mm->mmap_sem);
785
786         msg_init(&ewq.msg);
787
788         ewq.msg.event = UFFD_EVENT_REMOVE;
789         ewq.msg.arg.remove.start = start;
790         ewq.msg.arg.remove.end = end;
791
792         userfaultfd_event_wait_completion(ctx, &ewq);
793
794         return false;
795 }
796
797 static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
798                           unsigned long start, unsigned long end)
799 {
800         struct userfaultfd_unmap_ctx *unmap_ctx;
801
802         list_for_each_entry(unmap_ctx, unmaps, list)
803                 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
804                     unmap_ctx->end == end)
805                         return true;
806
807         return false;
808 }
809
810 int userfaultfd_unmap_prep(struct vm_area_struct *vma,
811                            unsigned long start, unsigned long end,
812                            struct list_head *unmaps)
813 {
814         for ( ; vma && vma->vm_start < end; vma = vma->vm_next) {
815                 struct userfaultfd_unmap_ctx *unmap_ctx;
816                 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
817
818                 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
819                     has_unmap_ctx(ctx, unmaps, start, end))
820                         continue;
821
822                 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
823                 if (!unmap_ctx)
824                         return -ENOMEM;
825
826                 userfaultfd_ctx_get(ctx);
827                 WRITE_ONCE(ctx->mmap_changing, true);
828                 unmap_ctx->ctx = ctx;
829                 unmap_ctx->start = start;
830                 unmap_ctx->end = end;
831                 list_add_tail(&unmap_ctx->list, unmaps);
832         }
833
834         return 0;
835 }
836
837 void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
838 {
839         struct userfaultfd_unmap_ctx *ctx, *n;
840         struct userfaultfd_wait_queue ewq;
841
842         list_for_each_entry_safe(ctx, n, uf, list) {
843                 msg_init(&ewq.msg);
844
845                 ewq.msg.event = UFFD_EVENT_UNMAP;
846                 ewq.msg.arg.remove.start = ctx->start;
847                 ewq.msg.arg.remove.end = ctx->end;
848
849                 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
850
851                 list_del(&ctx->list);
852                 kfree(ctx);
853         }
854 }
855
856 static int userfaultfd_release(struct inode *inode, struct file *file)
857 {
858         struct userfaultfd_ctx *ctx = file->private_data;
859         struct mm_struct *mm = ctx->mm;
860         struct vm_area_struct *vma, *prev;
861         /* len == 0 means wake all */
862         struct userfaultfd_wake_range range = { .len = 0, };
863         unsigned long new_flags;
864
865         WRITE_ONCE(ctx->released, true);
866
867         if (!mmget_not_zero(mm))
868                 goto wakeup;
869
870         /*
871          * Flush page faults out of all CPUs. NOTE: all page faults
872          * must be retried without returning VM_FAULT_SIGBUS if
873          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
874          * changes while handle_userfault released the mmap_sem. So
875          * it's critical that released is set to true (above), before
876          * taking the mmap_sem for writing.
877          */
878         down_write(&mm->mmap_sem);
879         prev = NULL;
880         for (vma = mm->mmap; vma; vma = vma->vm_next) {
881                 cond_resched();
882                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
883                        !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
884                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
885                         prev = vma;
886                         continue;
887                 }
888                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
889                 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
890                                  new_flags, vma->anon_vma,
891                                  vma->vm_file, vma->vm_pgoff,
892                                  vma_policy(vma),
893                                  NULL_VM_UFFD_CTX);
894                 if (prev)
895                         vma = prev;
896                 else
897                         prev = vma;
898                 vma->vm_flags = new_flags;
899                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
900         }
901         up_write(&mm->mmap_sem);
902         mmput(mm);
903 wakeup:
904         /*
905          * After no new page faults can wait on this fault_*wqh, flush
906          * the last page faults that may have been already waiting on
907          * the fault_*wqh.
908          */
909         spin_lock(&ctx->fault_pending_wqh.lock);
910         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
911         __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
912         spin_unlock(&ctx->fault_pending_wqh.lock);
913
914         /* Flush pending events that may still wait on event_wqh */
915         wake_up_all(&ctx->event_wqh);
916
917         wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
918         userfaultfd_ctx_put(ctx);
919         return 0;
920 }
921
922 /* fault_pending_wqh.lock must be hold by the caller */
923 static inline struct userfaultfd_wait_queue *find_userfault_in(
924                 wait_queue_head_t *wqh)
925 {
926         wait_queue_entry_t *wq;
927         struct userfaultfd_wait_queue *uwq;
928
929         VM_BUG_ON(!spin_is_locked(&wqh->lock));
930
931         uwq = NULL;
932         if (!waitqueue_active(wqh))
933                 goto out;
934         /* walk in reverse to provide FIFO behavior to read userfaults */
935         wq = list_last_entry(&wqh->head, typeof(*wq), entry);
936         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
937 out:
938         return uwq;
939 }
940
941 static inline struct userfaultfd_wait_queue *find_userfault(
942                 struct userfaultfd_ctx *ctx)
943 {
944         return find_userfault_in(&ctx->fault_pending_wqh);
945 }
946
947 static inline struct userfaultfd_wait_queue *find_userfault_evt(
948                 struct userfaultfd_ctx *ctx)
949 {
950         return find_userfault_in(&ctx->event_wqh);
951 }
952
953 static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
954 {
955         struct userfaultfd_ctx *ctx = file->private_data;
956         __poll_t ret;
957
958         poll_wait(file, &ctx->fd_wqh, wait);
959
960         switch (ctx->state) {
961         case UFFD_STATE_WAIT_API:
962                 return EPOLLERR;
963         case UFFD_STATE_RUNNING:
964                 /*
965                  * poll() never guarantees that read won't block.
966                  * userfaults can be waken before they're read().
967                  */
968                 if (unlikely(!(file->f_flags & O_NONBLOCK)))
969                         return EPOLLERR;
970                 /*
971                  * lockless access to see if there are pending faults
972                  * __pollwait last action is the add_wait_queue but
973                  * the spin_unlock would allow the waitqueue_active to
974                  * pass above the actual list_add inside
975                  * add_wait_queue critical section. So use a full
976                  * memory barrier to serialize the list_add write of
977                  * add_wait_queue() with the waitqueue_active read
978                  * below.
979                  */
980                 ret = 0;
981                 smp_mb();
982                 if (waitqueue_active(&ctx->fault_pending_wqh))
983                         ret = EPOLLIN;
984                 else if (waitqueue_active(&ctx->event_wqh))
985                         ret = EPOLLIN;
986
987                 return ret;
988         default:
989                 WARN_ON_ONCE(1);
990                 return EPOLLERR;
991         }
992 }
993
994 static const struct file_operations userfaultfd_fops;
995
996 static int resolve_userfault_fork(struct userfaultfd_ctx *ctx,
997                                   struct userfaultfd_ctx *new,
998                                   struct uffd_msg *msg)
999 {
1000         int fd;
1001
1002         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, new,
1003                               O_RDWR | (new->flags & UFFD_SHARED_FCNTL_FLAGS));
1004         if (fd < 0)
1005                 return fd;
1006
1007         msg->arg.reserved.reserved1 = 0;
1008         msg->arg.fork.ufd = fd;
1009         return 0;
1010 }
1011
1012 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1013                                     struct uffd_msg *msg)
1014 {
1015         ssize_t ret;
1016         DECLARE_WAITQUEUE(wait, current);
1017         struct userfaultfd_wait_queue *uwq;
1018         /*
1019          * Handling fork event requires sleeping operations, so
1020          * we drop the event_wqh lock, then do these ops, then
1021          * lock it back and wake up the waiter. While the lock is
1022          * dropped the ewq may go away so we keep track of it
1023          * carefully.
1024          */
1025         LIST_HEAD(fork_event);
1026         struct userfaultfd_ctx *fork_nctx = NULL;
1027
1028         /* always take the fd_wqh lock before the fault_pending_wqh lock */
1029         spin_lock_irq(&ctx->fd_wqh.lock);
1030         __add_wait_queue(&ctx->fd_wqh, &wait);
1031         for (;;) {
1032                 set_current_state(TASK_INTERRUPTIBLE);
1033                 spin_lock(&ctx->fault_pending_wqh.lock);
1034                 uwq = find_userfault(ctx);
1035                 if (uwq) {
1036                         /*
1037                          * Use a seqcount to repeat the lockless check
1038                          * in wake_userfault() to avoid missing
1039                          * wakeups because during the refile both
1040                          * waitqueue could become empty if this is the
1041                          * only userfault.
1042                          */
1043                         write_seqcount_begin(&ctx->refile_seq);
1044
1045                         /*
1046                          * The fault_pending_wqh.lock prevents the uwq
1047                          * to disappear from under us.
1048                          *
1049                          * Refile this userfault from
1050                          * fault_pending_wqh to fault_wqh, it's not
1051                          * pending anymore after we read it.
1052                          *
1053                          * Use list_del() by hand (as
1054                          * userfaultfd_wake_function also uses
1055                          * list_del_init() by hand) to be sure nobody
1056                          * changes __remove_wait_queue() to use
1057                          * list_del_init() in turn breaking the
1058                          * !list_empty_careful() check in
1059                          * handle_userfault(). The uwq->wq.head list
1060                          * must never be empty at any time during the
1061                          * refile, or the waitqueue could disappear
1062                          * from under us. The "wait_queue_head_t"
1063                          * parameter of __remove_wait_queue() is unused
1064                          * anyway.
1065                          */
1066                         list_del(&uwq->wq.entry);
1067                         add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1068
1069                         write_seqcount_end(&ctx->refile_seq);
1070
1071                         /* careful to always initialize msg if ret == 0 */
1072                         *msg = uwq->msg;
1073                         spin_unlock(&ctx->fault_pending_wqh.lock);
1074                         ret = 0;
1075                         break;
1076                 }
1077                 spin_unlock(&ctx->fault_pending_wqh.lock);
1078
1079                 spin_lock(&ctx->event_wqh.lock);
1080                 uwq = find_userfault_evt(ctx);
1081                 if (uwq) {
1082                         *msg = uwq->msg;
1083
1084                         if (uwq->msg.event == UFFD_EVENT_FORK) {
1085                                 fork_nctx = (struct userfaultfd_ctx *)
1086                                         (unsigned long)
1087                                         uwq->msg.arg.reserved.reserved1;
1088                                 list_move(&uwq->wq.entry, &fork_event);
1089                                 /*
1090                                  * fork_nctx can be freed as soon as
1091                                  * we drop the lock, unless we take a
1092                                  * reference on it.
1093                                  */
1094                                 userfaultfd_ctx_get(fork_nctx);
1095                                 spin_unlock(&ctx->event_wqh.lock);
1096                                 ret = 0;
1097                                 break;
1098                         }
1099
1100                         userfaultfd_event_complete(ctx, uwq);
1101                         spin_unlock(&ctx->event_wqh.lock);
1102                         ret = 0;
1103                         break;
1104                 }
1105                 spin_unlock(&ctx->event_wqh.lock);
1106
1107                 if (signal_pending(current)) {
1108                         ret = -ERESTARTSYS;
1109                         break;
1110                 }
1111                 if (no_wait) {
1112                         ret = -EAGAIN;
1113                         break;
1114                 }
1115                 spin_unlock_irq(&ctx->fd_wqh.lock);
1116                 schedule();
1117                 spin_lock_irq(&ctx->fd_wqh.lock);
1118         }
1119         __remove_wait_queue(&ctx->fd_wqh, &wait);
1120         __set_current_state(TASK_RUNNING);
1121         spin_unlock_irq(&ctx->fd_wqh.lock);
1122
1123         if (!ret && msg->event == UFFD_EVENT_FORK) {
1124                 ret = resolve_userfault_fork(ctx, fork_nctx, msg);
1125                 spin_lock(&ctx->event_wqh.lock);
1126                 if (!list_empty(&fork_event)) {
1127                         /*
1128                          * The fork thread didn't abort, so we can
1129                          * drop the temporary refcount.
1130                          */
1131                         userfaultfd_ctx_put(fork_nctx);
1132
1133                         uwq = list_first_entry(&fork_event,
1134                                                typeof(*uwq),
1135                                                wq.entry);
1136                         /*
1137                          * If fork_event list wasn't empty and in turn
1138                          * the event wasn't already released by fork
1139                          * (the event is allocated on fork kernel
1140                          * stack), put the event back to its place in
1141                          * the event_wq. fork_event head will be freed
1142                          * as soon as we return so the event cannot
1143                          * stay queued there no matter the current
1144                          * "ret" value.
1145                          */
1146                         list_del(&uwq->wq.entry);
1147                         __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1148
1149                         /*
1150                          * Leave the event in the waitqueue and report
1151                          * error to userland if we failed to resolve
1152                          * the userfault fork.
1153                          */
1154                         if (likely(!ret))
1155                                 userfaultfd_event_complete(ctx, uwq);
1156                 } else {
1157                         /*
1158                          * Here the fork thread aborted and the
1159                          * refcount from the fork thread on fork_nctx
1160                          * has already been released. We still hold
1161                          * the reference we took before releasing the
1162                          * lock above. If resolve_userfault_fork
1163                          * failed we've to drop it because the
1164                          * fork_nctx has to be freed in such case. If
1165                          * it succeeded we'll hold it because the new
1166                          * uffd references it.
1167                          */
1168                         if (ret)
1169                                 userfaultfd_ctx_put(fork_nctx);
1170                 }
1171                 spin_unlock(&ctx->event_wqh.lock);
1172         }
1173
1174         return ret;
1175 }
1176
1177 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1178                                 size_t count, loff_t *ppos)
1179 {
1180         struct userfaultfd_ctx *ctx = file->private_data;
1181         ssize_t _ret, ret = 0;
1182         struct uffd_msg msg;
1183         int no_wait = file->f_flags & O_NONBLOCK;
1184
1185         if (ctx->state == UFFD_STATE_WAIT_API)
1186                 return -EINVAL;
1187
1188         for (;;) {
1189                 if (count < sizeof(msg))
1190                         return ret ? ret : -EINVAL;
1191                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
1192                 if (_ret < 0)
1193                         return ret ? ret : _ret;
1194                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1195                         return ret ? ret : -EFAULT;
1196                 ret += sizeof(msg);
1197                 buf += sizeof(msg);
1198                 count -= sizeof(msg);
1199                 /*
1200                  * Allow to read more than one fault at time but only
1201                  * block if waiting for the very first one.
1202                  */
1203                 no_wait = O_NONBLOCK;
1204         }
1205 }
1206
1207 static void __wake_userfault(struct userfaultfd_ctx *ctx,
1208                              struct userfaultfd_wake_range *range)
1209 {
1210         spin_lock(&ctx->fault_pending_wqh.lock);
1211         /* wake all in the range and autoremove */
1212         if (waitqueue_active(&ctx->fault_pending_wqh))
1213                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1214                                      range);
1215         if (waitqueue_active(&ctx->fault_wqh))
1216                 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1217         spin_unlock(&ctx->fault_pending_wqh.lock);
1218 }
1219
1220 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1221                                            struct userfaultfd_wake_range *range)
1222 {
1223         unsigned seq;
1224         bool need_wakeup;
1225
1226         /*
1227          * To be sure waitqueue_active() is not reordered by the CPU
1228          * before the pagetable update, use an explicit SMP memory
1229          * barrier here. PT lock release or up_read(mmap_sem) still
1230          * have release semantics that can allow the
1231          * waitqueue_active() to be reordered before the pte update.
1232          */
1233         smp_mb();
1234
1235         /*
1236          * Use waitqueue_active because it's very frequent to
1237          * change the address space atomically even if there are no
1238          * userfaults yet. So we take the spinlock only when we're
1239          * sure we've userfaults to wake.
1240          */
1241         do {
1242                 seq = read_seqcount_begin(&ctx->refile_seq);
1243                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1244                         waitqueue_active(&ctx->fault_wqh);
1245                 cond_resched();
1246         } while (read_seqcount_retry(&ctx->refile_seq, seq));
1247         if (need_wakeup)
1248                 __wake_userfault(ctx, range);
1249 }
1250
1251 static __always_inline int validate_range(struct mm_struct *mm,
1252                                           __u64 start, __u64 len)
1253 {
1254         __u64 task_size = mm->task_size;
1255
1256         if (start & ~PAGE_MASK)
1257                 return -EINVAL;
1258         if (len & ~PAGE_MASK)
1259                 return -EINVAL;
1260         if (!len)
1261                 return -EINVAL;
1262         if (start < mmap_min_addr)
1263                 return -EINVAL;
1264         if (start >= task_size)
1265                 return -EINVAL;
1266         if (len > task_size - start)
1267                 return -EINVAL;
1268         return 0;
1269 }
1270
1271 static inline bool vma_can_userfault(struct vm_area_struct *vma)
1272 {
1273         return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
1274                 vma_is_shmem(vma);
1275 }
1276
1277 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1278                                 unsigned long arg)
1279 {
1280         struct mm_struct *mm = ctx->mm;
1281         struct vm_area_struct *vma, *prev, *cur;
1282         int ret;
1283         struct uffdio_register uffdio_register;
1284         struct uffdio_register __user *user_uffdio_register;
1285         unsigned long vm_flags, new_flags;
1286         bool found;
1287         bool basic_ioctls;
1288         unsigned long start, end, vma_end;
1289
1290         user_uffdio_register = (struct uffdio_register __user *) arg;
1291
1292         ret = -EFAULT;
1293         if (copy_from_user(&uffdio_register, user_uffdio_register,
1294                            sizeof(uffdio_register)-sizeof(__u64)))
1295                 goto out;
1296
1297         ret = -EINVAL;
1298         if (!uffdio_register.mode)
1299                 goto out;
1300         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
1301                                      UFFDIO_REGISTER_MODE_WP))
1302                 goto out;
1303         vm_flags = 0;
1304         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1305                 vm_flags |= VM_UFFD_MISSING;
1306         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1307                 vm_flags |= VM_UFFD_WP;
1308                 /*
1309                  * FIXME: remove the below error constraint by
1310                  * implementing the wprotect tracking mode.
1311                  */
1312                 ret = -EINVAL;
1313                 goto out;
1314         }
1315
1316         ret = validate_range(mm, uffdio_register.range.start,
1317                              uffdio_register.range.len);
1318         if (ret)
1319                 goto out;
1320
1321         start = uffdio_register.range.start;
1322         end = start + uffdio_register.range.len;
1323
1324         ret = -ENOMEM;
1325         if (!mmget_not_zero(mm))
1326                 goto out;
1327
1328         down_write(&mm->mmap_sem);
1329         vma = find_vma_prev(mm, start, &prev);
1330         if (!vma)
1331                 goto out_unlock;
1332
1333         /* check that there's at least one vma in the range */
1334         ret = -EINVAL;
1335         if (vma->vm_start >= end)
1336                 goto out_unlock;
1337
1338         /*
1339          * If the first vma contains huge pages, make sure start address
1340          * is aligned to huge page size.
1341          */
1342         if (is_vm_hugetlb_page(vma)) {
1343                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1344
1345                 if (start & (vma_hpagesize - 1))
1346                         goto out_unlock;
1347         }
1348
1349         /*
1350          * Search for not compatible vmas.
1351          */
1352         found = false;
1353         basic_ioctls = false;
1354         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1355                 cond_resched();
1356
1357                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1358                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1359
1360                 /* check not compatible vmas */
1361                 ret = -EINVAL;
1362                 if (!vma_can_userfault(cur))
1363                         goto out_unlock;
1364
1365                 /*
1366                  * UFFDIO_COPY will fill file holes even without
1367                  * PROT_WRITE. This check enforces that if this is a
1368                  * MAP_SHARED, the process has write permission to the backing
1369                  * file. If VM_MAYWRITE is set it also enforces that on a
1370                  * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1371                  * F_WRITE_SEAL can be taken until the vma is destroyed.
1372                  */
1373                 ret = -EPERM;
1374                 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1375                         goto out_unlock;
1376
1377                 /*
1378                  * If this vma contains ending address, and huge pages
1379                  * check alignment.
1380                  */
1381                 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1382                     end > cur->vm_start) {
1383                         unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1384
1385                         ret = -EINVAL;
1386
1387                         if (end & (vma_hpagesize - 1))
1388                                 goto out_unlock;
1389                 }
1390
1391                 /*
1392                  * Check that this vma isn't already owned by a
1393                  * different userfaultfd. We can't allow more than one
1394                  * userfaultfd to own a single vma simultaneously or we
1395                  * wouldn't know which one to deliver the userfaults to.
1396                  */
1397                 ret = -EBUSY;
1398                 if (cur->vm_userfaultfd_ctx.ctx &&
1399                     cur->vm_userfaultfd_ctx.ctx != ctx)
1400                         goto out_unlock;
1401
1402                 /*
1403                  * Note vmas containing huge pages
1404                  */
1405                 if (is_vm_hugetlb_page(cur))
1406                         basic_ioctls = true;
1407
1408                 found = true;
1409         }
1410         BUG_ON(!found);
1411
1412         if (vma->vm_start < start)
1413                 prev = vma;
1414
1415         ret = 0;
1416         do {
1417                 cond_resched();
1418
1419                 BUG_ON(!vma_can_userfault(vma));
1420                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1421                        vma->vm_userfaultfd_ctx.ctx != ctx);
1422                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1423
1424                 /*
1425                  * Nothing to do: this vma is already registered into this
1426                  * userfaultfd and with the right tracking mode too.
1427                  */
1428                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1429                     (vma->vm_flags & vm_flags) == vm_flags)
1430                         goto skip;
1431
1432                 if (vma->vm_start > start)
1433                         start = vma->vm_start;
1434                 vma_end = min(end, vma->vm_end);
1435
1436                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
1437                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1438                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1439                                  vma_policy(vma),
1440                                  ((struct vm_userfaultfd_ctx){ ctx }));
1441                 if (prev) {
1442                         vma = prev;
1443                         goto next;
1444                 }
1445                 if (vma->vm_start < start) {
1446                         ret = split_vma(mm, vma, start, 1);
1447                         if (ret)
1448                                 break;
1449                 }
1450                 if (vma->vm_end > end) {
1451                         ret = split_vma(mm, vma, end, 0);
1452                         if (ret)
1453                                 break;
1454                 }
1455         next:
1456                 /*
1457                  * In the vma_merge() successful mprotect-like case 8:
1458                  * the next vma was merged into the current one and
1459                  * the current one has not been updated yet.
1460                  */
1461                 vma->vm_flags = new_flags;
1462                 vma->vm_userfaultfd_ctx.ctx = ctx;
1463
1464         skip:
1465                 prev = vma;
1466                 start = vma->vm_end;
1467                 vma = vma->vm_next;
1468         } while (vma && vma->vm_start < end);
1469 out_unlock:
1470         up_write(&mm->mmap_sem);
1471         mmput(mm);
1472         if (!ret) {
1473                 /*
1474                  * Now that we scanned all vmas we can already tell
1475                  * userland which ioctls methods are guaranteed to
1476                  * succeed on this range.
1477                  */
1478                 if (put_user(basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1479                              UFFD_API_RANGE_IOCTLS,
1480                              &user_uffdio_register->ioctls))
1481                         ret = -EFAULT;
1482         }
1483 out:
1484         return ret;
1485 }
1486
1487 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1488                                   unsigned long arg)
1489 {
1490         struct mm_struct *mm = ctx->mm;
1491         struct vm_area_struct *vma, *prev, *cur;
1492         int ret;
1493         struct uffdio_range uffdio_unregister;
1494         unsigned long new_flags;
1495         bool found;
1496         unsigned long start, end, vma_end;
1497         const void __user *buf = (void __user *)arg;
1498
1499         ret = -EFAULT;
1500         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1501                 goto out;
1502
1503         ret = validate_range(mm, uffdio_unregister.start,
1504                              uffdio_unregister.len);
1505         if (ret)
1506                 goto out;
1507
1508         start = uffdio_unregister.start;
1509         end = start + uffdio_unregister.len;
1510
1511         ret = -ENOMEM;
1512         if (!mmget_not_zero(mm))
1513                 goto out;
1514
1515         down_write(&mm->mmap_sem);
1516         vma = find_vma_prev(mm, start, &prev);
1517         if (!vma)
1518                 goto out_unlock;
1519
1520         /* check that there's at least one vma in the range */
1521         ret = -EINVAL;
1522         if (vma->vm_start >= end)
1523                 goto out_unlock;
1524
1525         /*
1526          * If the first vma contains huge pages, make sure start address
1527          * is aligned to huge page size.
1528          */
1529         if (is_vm_hugetlb_page(vma)) {
1530                 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1531
1532                 if (start & (vma_hpagesize - 1))
1533                         goto out_unlock;
1534         }
1535
1536         /*
1537          * Search for not compatible vmas.
1538          */
1539         found = false;
1540         ret = -EINVAL;
1541         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
1542                 cond_resched();
1543
1544                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1545                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
1546
1547                 /*
1548                  * Check not compatible vmas, not strictly required
1549                  * here as not compatible vmas cannot have an
1550                  * userfaultfd_ctx registered on them, but this
1551                  * provides for more strict behavior to notice
1552                  * unregistration errors.
1553                  */
1554                 if (!vma_can_userfault(cur))
1555                         goto out_unlock;
1556
1557                 found = true;
1558         }
1559         BUG_ON(!found);
1560
1561         if (vma->vm_start < start)
1562                 prev = vma;
1563
1564         ret = 0;
1565         do {
1566                 cond_resched();
1567
1568                 BUG_ON(!vma_can_userfault(vma));
1569
1570                 /*
1571                  * Nothing to do: this vma is already registered into this
1572                  * userfaultfd and with the right tracking mode too.
1573                  */
1574                 if (!vma->vm_userfaultfd_ctx.ctx)
1575                         goto skip;
1576
1577                 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1578
1579                 if (vma->vm_start > start)
1580                         start = vma->vm_start;
1581                 vma_end = min(end, vma->vm_end);
1582
1583                 if (userfaultfd_missing(vma)) {
1584                         /*
1585                          * Wake any concurrent pending userfault while
1586                          * we unregister, so they will not hang
1587                          * permanently and it avoids userland to call
1588                          * UFFDIO_WAKE explicitly.
1589                          */
1590                         struct userfaultfd_wake_range range;
1591                         range.start = start;
1592                         range.len = vma_end - start;
1593                         wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1594                 }
1595
1596                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1597                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1598                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1599                                  vma_policy(vma),
1600                                  NULL_VM_UFFD_CTX);
1601                 if (prev) {
1602                         vma = prev;
1603                         goto next;
1604                 }
1605                 if (vma->vm_start < start) {
1606                         ret = split_vma(mm, vma, start, 1);
1607                         if (ret)
1608                                 break;
1609                 }
1610                 if (vma->vm_end > end) {
1611                         ret = split_vma(mm, vma, end, 0);
1612                         if (ret)
1613                                 break;
1614                 }
1615         next:
1616                 /*
1617                  * In the vma_merge() successful mprotect-like case 8:
1618                  * the next vma was merged into the current one and
1619                  * the current one has not been updated yet.
1620                  */
1621                 vma->vm_flags = new_flags;
1622                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1623
1624         skip:
1625                 prev = vma;
1626                 start = vma->vm_end;
1627                 vma = vma->vm_next;
1628         } while (vma && vma->vm_start < end);
1629 out_unlock:
1630         up_write(&mm->mmap_sem);
1631         mmput(mm);
1632 out:
1633         return ret;
1634 }
1635
1636 /*
1637  * userfaultfd_wake may be used in combination with the
1638  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1639  */
1640 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1641                             unsigned long arg)
1642 {
1643         int ret;
1644         struct uffdio_range uffdio_wake;
1645         struct userfaultfd_wake_range range;
1646         const void __user *buf = (void __user *)arg;
1647
1648         ret = -EFAULT;
1649         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1650                 goto out;
1651
1652         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1653         if (ret)
1654                 goto out;
1655
1656         range.start = uffdio_wake.start;
1657         range.len = uffdio_wake.len;
1658
1659         /*
1660          * len == 0 means wake all and we don't want to wake all here,
1661          * so check it again to be sure.
1662          */
1663         VM_BUG_ON(!range.len);
1664
1665         wake_userfault(ctx, &range);
1666         ret = 0;
1667
1668 out:
1669         return ret;
1670 }
1671
1672 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1673                             unsigned long arg)
1674 {
1675         __s64 ret;
1676         struct uffdio_copy uffdio_copy;
1677         struct uffdio_copy __user *user_uffdio_copy;
1678         struct userfaultfd_wake_range range;
1679
1680         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1681
1682         ret = -EAGAIN;
1683         if (READ_ONCE(ctx->mmap_changing))
1684                 goto out;
1685
1686         ret = -EFAULT;
1687         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1688                            /* don't copy "copy" last field */
1689                            sizeof(uffdio_copy)-sizeof(__s64)))
1690                 goto out;
1691
1692         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1693         if (ret)
1694                 goto out;
1695         /*
1696          * double check for wraparound just in case. copy_from_user()
1697          * will later check uffdio_copy.src + uffdio_copy.len to fit
1698          * in the userland range.
1699          */
1700         ret = -EINVAL;
1701         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1702                 goto out;
1703         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1704                 goto out;
1705         if (mmget_not_zero(ctx->mm)) {
1706                 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1707                                    uffdio_copy.len, &ctx->mmap_changing);
1708                 mmput(ctx->mm);
1709         } else {
1710                 return -ESRCH;
1711         }
1712         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1713                 return -EFAULT;
1714         if (ret < 0)
1715                 goto out;
1716         BUG_ON(!ret);
1717         /* len == 0 would wake all */
1718         range.len = ret;
1719         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1720                 range.start = uffdio_copy.dst;
1721                 wake_userfault(ctx, &range);
1722         }
1723         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1724 out:
1725         return ret;
1726 }
1727
1728 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1729                                 unsigned long arg)
1730 {
1731         __s64 ret;
1732         struct uffdio_zeropage uffdio_zeropage;
1733         struct uffdio_zeropage __user *user_uffdio_zeropage;
1734         struct userfaultfd_wake_range range;
1735
1736         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1737
1738         ret = -EAGAIN;
1739         if (READ_ONCE(ctx->mmap_changing))
1740                 goto out;
1741
1742         ret = -EFAULT;
1743         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1744                            /* don't copy "zeropage" last field */
1745                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1746                 goto out;
1747
1748         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1749                              uffdio_zeropage.range.len);
1750         if (ret)
1751                 goto out;
1752         ret = -EINVAL;
1753         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1754                 goto out;
1755
1756         if (mmget_not_zero(ctx->mm)) {
1757                 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1758                                      uffdio_zeropage.range.len,
1759                                      &ctx->mmap_changing);
1760                 mmput(ctx->mm);
1761         } else {
1762                 return -ESRCH;
1763         }
1764         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1765                 return -EFAULT;
1766         if (ret < 0)
1767                 goto out;
1768         /* len == 0 would wake all */
1769         BUG_ON(!ret);
1770         range.len = ret;
1771         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1772                 range.start = uffdio_zeropage.range.start;
1773                 wake_userfault(ctx, &range);
1774         }
1775         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1776 out:
1777         return ret;
1778 }
1779
1780 static inline unsigned int uffd_ctx_features(__u64 user_features)
1781 {
1782         /*
1783          * For the current set of features the bits just coincide
1784          */
1785         return (unsigned int)user_features;
1786 }
1787
1788 /*
1789  * userland asks for a certain API version and we return which bits
1790  * and ioctl commands are implemented in this kernel for such API
1791  * version or -EINVAL if unknown.
1792  */
1793 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1794                            unsigned long arg)
1795 {
1796         struct uffdio_api uffdio_api;
1797         void __user *buf = (void __user *)arg;
1798         int ret;
1799         __u64 features;
1800
1801         ret = -EINVAL;
1802         if (ctx->state != UFFD_STATE_WAIT_API)
1803                 goto out;
1804         ret = -EFAULT;
1805         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1806                 goto out;
1807         features = uffdio_api.features;
1808         if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES)) {
1809                 memset(&uffdio_api, 0, sizeof(uffdio_api));
1810                 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1811                         goto out;
1812                 ret = -EINVAL;
1813                 goto out;
1814         }
1815         /* report all available features and ioctls to userland */
1816         uffdio_api.features = UFFD_API_FEATURES;
1817         uffdio_api.ioctls = UFFD_API_IOCTLS;
1818         ret = -EFAULT;
1819         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1820                 goto out;
1821         ctx->state = UFFD_STATE_RUNNING;
1822         /* only enable the requested features for this uffd context */
1823         ctx->features = uffd_ctx_features(features);
1824         ret = 0;
1825 out:
1826         return ret;
1827 }
1828
1829 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1830                               unsigned long arg)
1831 {
1832         int ret = -EINVAL;
1833         struct userfaultfd_ctx *ctx = file->private_data;
1834
1835         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1836                 return -EINVAL;
1837
1838         switch(cmd) {
1839         case UFFDIO_API:
1840                 ret = userfaultfd_api(ctx, arg);
1841                 break;
1842         case UFFDIO_REGISTER:
1843                 ret = userfaultfd_register(ctx, arg);
1844                 break;
1845         case UFFDIO_UNREGISTER:
1846                 ret = userfaultfd_unregister(ctx, arg);
1847                 break;
1848         case UFFDIO_WAKE:
1849                 ret = userfaultfd_wake(ctx, arg);
1850                 break;
1851         case UFFDIO_COPY:
1852                 ret = userfaultfd_copy(ctx, arg);
1853                 break;
1854         case UFFDIO_ZEROPAGE:
1855                 ret = userfaultfd_zeropage(ctx, arg);
1856                 break;
1857         }
1858         return ret;
1859 }
1860
1861 #ifdef CONFIG_PROC_FS
1862 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1863 {
1864         struct userfaultfd_ctx *ctx = f->private_data;
1865         wait_queue_entry_t *wq;
1866         unsigned long pending = 0, total = 0;
1867
1868         spin_lock(&ctx->fault_pending_wqh.lock);
1869         list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
1870                 pending++;
1871                 total++;
1872         }
1873         list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
1874                 total++;
1875         }
1876         spin_unlock(&ctx->fault_pending_wqh.lock);
1877
1878         /*
1879          * If more protocols will be added, there will be all shown
1880          * separated by a space. Like this:
1881          *      protocols: aa:... bb:...
1882          */
1883         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1884                    pending, total, UFFD_API, ctx->features,
1885                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1886 }
1887 #endif
1888
1889 static const struct file_operations userfaultfd_fops = {
1890 #ifdef CONFIG_PROC_FS
1891         .show_fdinfo    = userfaultfd_show_fdinfo,
1892 #endif
1893         .release        = userfaultfd_release,
1894         .poll           = userfaultfd_poll,
1895         .read           = userfaultfd_read,
1896         .unlocked_ioctl = userfaultfd_ioctl,
1897         .compat_ioctl   = userfaultfd_ioctl,
1898         .llseek         = noop_llseek,
1899 };
1900
1901 static void init_once_userfaultfd_ctx(void *mem)
1902 {
1903         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1904
1905         init_waitqueue_head(&ctx->fault_pending_wqh);
1906         init_waitqueue_head(&ctx->fault_wqh);
1907         init_waitqueue_head(&ctx->event_wqh);
1908         init_waitqueue_head(&ctx->fd_wqh);
1909         seqcount_init(&ctx->refile_seq);
1910 }
1911
1912 SYSCALL_DEFINE1(userfaultfd, int, flags)
1913 {
1914         struct userfaultfd_ctx *ctx;
1915         int fd;
1916
1917         BUG_ON(!current->mm);
1918
1919         /* Check the UFFD_* constants for consistency.  */
1920         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1921         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1922
1923         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1924                 return -EINVAL;
1925
1926         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1927         if (!ctx)
1928                 return -ENOMEM;
1929
1930         atomic_set(&ctx->refcount, 1);
1931         ctx->flags = flags;
1932         ctx->features = 0;
1933         ctx->state = UFFD_STATE_WAIT_API;
1934         ctx->released = false;
1935         ctx->mmap_changing = false;
1936         ctx->mm = current->mm;
1937         /* prevent the mm struct to be freed */
1938         mmgrab(ctx->mm);
1939
1940         fd = anon_inode_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
1941                               O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1942         if (fd < 0) {
1943                 mmdrop(ctx->mm);
1944                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1945         }
1946         return fd;
1947 }
1948
1949 static int __init userfaultfd_init(void)
1950 {
1951         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1952                                                 sizeof(struct userfaultfd_ctx),
1953                                                 0,
1954                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1955                                                 init_once_userfaultfd_ctx);
1956         return 0;
1957 }
1958 __initcall(userfaultfd_init);