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TOMOYO Linux Cross Reference
Linux/fs/userfaultfd.c

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  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/hashtable.h>
 16 #include <linux/sched.h>
 17 #include <linux/mm.h>
 18 #include <linux/poll.h>
 19 #include <linux/slab.h>
 20 #include <linux/seq_file.h>
 21 #include <linux/file.h>
 22 #include <linux/bug.h>
 23 #include <linux/anon_inodes.h>
 24 #include <linux/syscalls.h>
 25 #include <linux/userfaultfd_k.h>
 26 #include <linux/mempolicy.h>
 27 #include <linux/ioctl.h>
 28 #include <linux/security.h>
 29 
 30 static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
 31 
 32 enum userfaultfd_state {
 33         UFFD_STATE_WAIT_API,
 34         UFFD_STATE_RUNNING,
 35 };
 36 
 37 /*
 38  * Start with fault_pending_wqh and fault_wqh so they're more likely
 39  * to be in the same cacheline.
 40  */
 41 struct userfaultfd_ctx {
 42         /* waitqueue head for the pending (i.e. not read) userfaults */
 43         wait_queue_head_t fault_pending_wqh;
 44         /* waitqueue head for the userfaults */
 45         wait_queue_head_t fault_wqh;
 46         /* waitqueue head for the pseudo fd to wakeup poll/read */
 47         wait_queue_head_t fd_wqh;
 48         /* a refile sequence protected by fault_pending_wqh lock */
 49         struct seqcount refile_seq;
 50         /* pseudo fd refcounting */
 51         atomic_t refcount;
 52         /* userfaultfd syscall flags */
 53         unsigned int flags;
 54         /* state machine */
 55         enum userfaultfd_state state;
 56         /* released */
 57         bool released;
 58         /* mm with one ore more vmas attached to this userfaultfd_ctx */
 59         struct mm_struct *mm;
 60 };
 61 
 62 struct userfaultfd_wait_queue {
 63         struct uffd_msg msg;
 64         wait_queue_t wq;
 65         struct userfaultfd_ctx *ctx;
 66 };
 67 
 68 struct userfaultfd_wake_range {
 69         unsigned long start;
 70         unsigned long len;
 71 };
 72 
 73 static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode,
 74                                      int wake_flags, void *key)
 75 {
 76         struct userfaultfd_wake_range *range = key;
 77         int ret;
 78         struct userfaultfd_wait_queue *uwq;
 79         unsigned long start, len;
 80 
 81         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
 82         ret = 0;
 83         /* len == 0 means wake all */
 84         start = range->start;
 85         len = range->len;
 86         if (len && (start > uwq->msg.arg.pagefault.address ||
 87                     start + len <= uwq->msg.arg.pagefault.address))
 88                 goto out;
 89         ret = wake_up_state(wq->private, mode);
 90         if (ret)
 91                 /*
 92                  * Wake only once, autoremove behavior.
 93                  *
 94                  * After the effect of list_del_init is visible to the
 95                  * other CPUs, the waitqueue may disappear from under
 96                  * us, see the !list_empty_careful() in
 97                  * handle_userfault(). try_to_wake_up() has an
 98                  * implicit smp_mb__before_spinlock, and the
 99                  * wq->private is read before calling the extern
100                  * function "wake_up_state" (which in turns calls
101                  * try_to_wake_up). While the spin_lock;spin_unlock;
102                  * wouldn't be enough, the smp_mb__before_spinlock is
103                  * enough to avoid an explicit smp_mb() here.
104                  */
105                 list_del_init(&wq->task_list);
106 out:
107         return ret;
108 }
109 
110 /**
111  * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
112  * context.
113  * @ctx: [in] Pointer to the userfaultfd context.
114  *
115  * Returns: In case of success, returns not zero.
116  */
117 static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
118 {
119         if (!atomic_inc_not_zero(&ctx->refcount))
120                 BUG();
121 }
122 
123 /**
124  * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
125  * context.
126  * @ctx: [in] Pointer to userfaultfd context.
127  *
128  * The userfaultfd context reference must have been previously acquired either
129  * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
130  */
131 static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
132 {
133         if (atomic_dec_and_test(&ctx->refcount)) {
134                 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
135                 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
136                 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
137                 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
138                 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
139                 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
140                 mmput(ctx->mm);
141                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
142         }
143 }
144 
145 static inline void msg_init(struct uffd_msg *msg)
146 {
147         BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
148         /*
149          * Must use memset to zero out the paddings or kernel data is
150          * leaked to userland.
151          */
152         memset(msg, 0, sizeof(struct uffd_msg));
153 }
154 
155 static inline struct uffd_msg userfault_msg(unsigned long address,
156                                             unsigned int flags,
157                                             unsigned long reason)
158 {
159         struct uffd_msg msg;
160         msg_init(&msg);
161         msg.event = UFFD_EVENT_PAGEFAULT;
162         msg.arg.pagefault.address = address;
163         if (flags & FAULT_FLAG_WRITE)
164                 /*
165                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the
166                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
167                  * was not set in a UFFD_EVENT_PAGEFAULT, it means it
168                  * was a read fault, otherwise if set it means it's
169                  * a write fault.
170                  */
171                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
172         if (reason & VM_UFFD_WP)
173                 /*
174                  * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
175                  * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
176                  * not set in a UFFD_EVENT_PAGEFAULT, it means it was
177                  * a missing fault, otherwise if set it means it's a
178                  * write protect fault.
179                  */
180                 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
181         return msg;
182 }
183 
184 /*
185  * Verify the pagetables are still not ok after having reigstered into
186  * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
187  * userfault that has already been resolved, if userfaultfd_read and
188  * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
189  * threads.
190  */
191 static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
192                                          unsigned long address,
193                                          unsigned long flags,
194                                          unsigned long reason)
195 {
196         struct mm_struct *mm = ctx->mm;
197         pgd_t *pgd;
198         pud_t *pud;
199         pmd_t *pmd, _pmd;
200         pte_t *pte;
201         bool ret = true;
202 
203         VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
204 
205         pgd = pgd_offset(mm, address);
206         if (!pgd_present(*pgd))
207                 goto out;
208         pud = pud_offset(pgd, address);
209         if (!pud_present(*pud))
210                 goto out;
211         pmd = pmd_offset(pud, address);
212         /*
213          * READ_ONCE must function as a barrier with narrower scope
214          * and it must be equivalent to:
215          *      _pmd = *pmd; barrier();
216          *
217          * This is to deal with the instability (as in
218          * pmd_trans_unstable) of the pmd.
219          */
220         _pmd = READ_ONCE(*pmd);
221         if (!pmd_present(_pmd))
222                 goto out;
223 
224         ret = false;
225         if (pmd_trans_huge(_pmd))
226                 goto out;
227 
228         /*
229          * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
230          * and use the standard pte_offset_map() instead of parsing _pmd.
231          */
232         pte = pte_offset_map(pmd, address);
233         /*
234          * Lockless access: we're in a wait_event so it's ok if it
235          * changes under us.
236          */
237         if (pte_none(*pte))
238                 ret = true;
239         pte_unmap(pte);
240 
241 out:
242         return ret;
243 }
244 
245 /*
246  * The locking rules involved in returning VM_FAULT_RETRY depending on
247  * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
248  * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
249  * recommendation in __lock_page_or_retry is not an understatement.
250  *
251  * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
252  * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
253  * not set.
254  *
255  * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
256  * set, VM_FAULT_RETRY can still be returned if and only if there are
257  * fatal_signal_pending()s, and the mmap_sem must be released before
258  * returning it.
259  */
260 int handle_userfault(struct vm_area_struct *vma, unsigned long address,
261                      unsigned int flags, unsigned long reason)
262 {
263         struct mm_struct *mm = vma->vm_mm;
264         struct userfaultfd_ctx *ctx;
265         struct userfaultfd_wait_queue uwq;
266         int ret;
267         bool must_wait, return_to_userland;
268 
269         BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
270 
271         ret = VM_FAULT_SIGBUS;
272         ctx = vma->vm_userfaultfd_ctx.ctx;
273         if (!ctx)
274                 goto out;
275 
276         BUG_ON(ctx->mm != mm);
277 
278         VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
279         VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
280 
281         /*
282          * If it's already released don't get it. This avoids to loop
283          * in __get_user_pages if userfaultfd_release waits on the
284          * caller of handle_userfault to release the mmap_sem.
285          */
286         if (unlikely(ACCESS_ONCE(ctx->released)))
287                 goto out;
288 
289         /*
290          * Check that we can return VM_FAULT_RETRY.
291          *
292          * NOTE: it should become possible to return VM_FAULT_RETRY
293          * even if FAULT_FLAG_TRIED is set without leading to gup()
294          * -EBUSY failures, if the userfaultfd is to be extended for
295          * VM_UFFD_WP tracking and we intend to arm the userfault
296          * without first stopping userland access to the memory. For
297          * VM_UFFD_MISSING userfaults this is enough for now.
298          */
299         if (unlikely(!(flags & FAULT_FLAG_ALLOW_RETRY))) {
300                 /*
301                  * Validate the invariant that nowait must allow retry
302                  * to be sure not to return SIGBUS erroneously on
303                  * nowait invocations.
304                  */
305                 BUG_ON(flags & FAULT_FLAG_RETRY_NOWAIT);
306 #ifdef CONFIG_DEBUG_VM
307                 if (printk_ratelimit()) {
308                         printk(KERN_WARNING
309                                "FAULT_FLAG_ALLOW_RETRY missing %x\n", flags);
310                         dump_stack();
311                 }
312 #endif
313                 goto out;
314         }
315 
316         /*
317          * Handle nowait, not much to do other than tell it to retry
318          * and wait.
319          */
320         ret = VM_FAULT_RETRY;
321         if (flags & FAULT_FLAG_RETRY_NOWAIT)
322                 goto out;
323 
324         /* take the reference before dropping the mmap_sem */
325         userfaultfd_ctx_get(ctx);
326 
327         init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
328         uwq.wq.private = current;
329         uwq.msg = userfault_msg(address, flags, reason);
330         uwq.ctx = ctx;
331 
332         return_to_userland = (flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
333                 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
334 
335         spin_lock(&ctx->fault_pending_wqh.lock);
336         /*
337          * After the __add_wait_queue the uwq is visible to userland
338          * through poll/read().
339          */
340         __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
341         /*
342          * The smp_mb() after __set_current_state prevents the reads
343          * following the spin_unlock to happen before the list_add in
344          * __add_wait_queue.
345          */
346         set_current_state(return_to_userland ? TASK_INTERRUPTIBLE :
347                           TASK_KILLABLE);
348         spin_unlock(&ctx->fault_pending_wqh.lock);
349 
350         must_wait = userfaultfd_must_wait(ctx, address, flags, reason);
351         up_read(&mm->mmap_sem);
352 
353         if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
354                    (return_to_userland ? !signal_pending(current) :
355                     !fatal_signal_pending(current)))) {
356                 wake_up_poll(&ctx->fd_wqh, POLLIN);
357                 schedule();
358                 ret |= VM_FAULT_MAJOR;
359         }
360 
361         __set_current_state(TASK_RUNNING);
362 
363         if (return_to_userland) {
364                 if (signal_pending(current) &&
365                     !fatal_signal_pending(current)) {
366                         /*
367                          * If we got a SIGSTOP or SIGCONT and this is
368                          * a normal userland page fault, just let
369                          * userland return so the signal will be
370                          * handled and gdb debugging works.  The page
371                          * fault code immediately after we return from
372                          * this function is going to release the
373                          * mmap_sem and it's not depending on it
374                          * (unlike gup would if we were not to return
375                          * VM_FAULT_RETRY).
376                          *
377                          * If a fatal signal is pending we still take
378                          * the streamlined VM_FAULT_RETRY failure path
379                          * and there's no need to retake the mmap_sem
380                          * in such case.
381                          */
382                         down_read(&mm->mmap_sem);
383                         ret = 0;
384                 }
385         }
386 
387         /*
388          * Here we race with the list_del; list_add in
389          * userfaultfd_ctx_read(), however because we don't ever run
390          * list_del_init() to refile across the two lists, the prev
391          * and next pointers will never point to self. list_add also
392          * would never let any of the two pointers to point to
393          * self. So list_empty_careful won't risk to see both pointers
394          * pointing to self at any time during the list refile. The
395          * only case where list_del_init() is called is the full
396          * removal in the wake function and there we don't re-list_add
397          * and it's fine not to block on the spinlock. The uwq on this
398          * kernel stack can be released after the list_del_init.
399          */
400         if (!list_empty_careful(&uwq.wq.task_list)) {
401                 spin_lock(&ctx->fault_pending_wqh.lock);
402                 /*
403                  * No need of list_del_init(), the uwq on the stack
404                  * will be freed shortly anyway.
405                  */
406                 list_del(&uwq.wq.task_list);
407                 spin_unlock(&ctx->fault_pending_wqh.lock);
408         }
409 
410         /*
411          * ctx may go away after this if the userfault pseudo fd is
412          * already released.
413          */
414         userfaultfd_ctx_put(ctx);
415 
416 out:
417         return ret;
418 }
419 
420 static int userfaultfd_release(struct inode *inode, struct file *file)
421 {
422         struct userfaultfd_ctx *ctx = file->private_data;
423         struct mm_struct *mm = ctx->mm;
424         struct vm_area_struct *vma, *prev;
425         /* len == 0 means wake all */
426         struct userfaultfd_wake_range range = { .len = 0, };
427         unsigned long new_flags;
428 
429         ACCESS_ONCE(ctx->released) = true;
430 
431         /*
432          * Flush page faults out of all CPUs. NOTE: all page faults
433          * must be retried without returning VM_FAULT_SIGBUS if
434          * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
435          * changes while handle_userfault released the mmap_sem. So
436          * it's critical that released is set to true (above), before
437          * taking the mmap_sem for writing.
438          */
439         down_write(&mm->mmap_sem);
440         prev = NULL;
441         for (vma = mm->mmap; vma; vma = vma->vm_next) {
442                 cond_resched();
443                 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
444                        !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
445                 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
446                         prev = vma;
447                         continue;
448                 }
449                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
450                 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
451                                  new_flags, vma->anon_vma,
452                                  vma->vm_file, vma->vm_pgoff,
453                                  vma_policy(vma),
454                                  NULL_VM_UFFD_CTX);
455                 if (prev)
456                         vma = prev;
457                 else
458                         prev = vma;
459                 vma->vm_flags = new_flags;
460                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
461         }
462         up_write(&mm->mmap_sem);
463 
464         /*
465          * After no new page faults can wait on this fault_*wqh, flush
466          * the last page faults that may have been already waiting on
467          * the fault_*wqh.
468          */
469         spin_lock(&ctx->fault_pending_wqh.lock);
470         __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
471         __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
472         spin_unlock(&ctx->fault_pending_wqh.lock);
473 
474         wake_up_poll(&ctx->fd_wqh, POLLHUP);
475         userfaultfd_ctx_put(ctx);
476         return 0;
477 }
478 
479 /* fault_pending_wqh.lock must be hold by the caller */
480 static inline struct userfaultfd_wait_queue *find_userfault(
481         struct userfaultfd_ctx *ctx)
482 {
483         wait_queue_t *wq;
484         struct userfaultfd_wait_queue *uwq;
485 
486         VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock));
487 
488         uwq = NULL;
489         if (!waitqueue_active(&ctx->fault_pending_wqh))
490                 goto out;
491         /* walk in reverse to provide FIFO behavior to read userfaults */
492         wq = list_last_entry(&ctx->fault_pending_wqh.task_list,
493                              typeof(*wq), task_list);
494         uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
495 out:
496         return uwq;
497 }
498 
499 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
500 {
501         struct userfaultfd_ctx *ctx = file->private_data;
502         unsigned int ret;
503 
504         poll_wait(file, &ctx->fd_wqh, wait);
505 
506         switch (ctx->state) {
507         case UFFD_STATE_WAIT_API:
508                 return POLLERR;
509         case UFFD_STATE_RUNNING:
510                 /*
511                  * poll() never guarantees that read won't block.
512                  * userfaults can be waken before they're read().
513                  */
514                 if (unlikely(!(file->f_flags & O_NONBLOCK)))
515                         return POLLERR;
516                 /*
517                  * lockless access to see if there are pending faults
518                  * __pollwait last action is the add_wait_queue but
519                  * the spin_unlock would allow the waitqueue_active to
520                  * pass above the actual list_add inside
521                  * add_wait_queue critical section. So use a full
522                  * memory barrier to serialize the list_add write of
523                  * add_wait_queue() with the waitqueue_active read
524                  * below.
525                  */
526                 ret = 0;
527                 smp_mb();
528                 if (waitqueue_active(&ctx->fault_pending_wqh))
529                         ret = POLLIN;
530                 return ret;
531         default:
532                 BUG();
533         }
534 }
535 
536 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
537                                     struct uffd_msg *msg)
538 {
539         ssize_t ret;
540         DECLARE_WAITQUEUE(wait, current);
541         struct userfaultfd_wait_queue *uwq;
542 
543         /* always take the fd_wqh lock before the fault_pending_wqh lock */
544         spin_lock(&ctx->fd_wqh.lock);
545         __add_wait_queue(&ctx->fd_wqh, &wait);
546         for (;;) {
547                 set_current_state(TASK_INTERRUPTIBLE);
548                 spin_lock(&ctx->fault_pending_wqh.lock);
549                 uwq = find_userfault(ctx);
550                 if (uwq) {
551                         /*
552                          * Use a seqcount to repeat the lockless check
553                          * in wake_userfault() to avoid missing
554                          * wakeups because during the refile both
555                          * waitqueue could become empty if this is the
556                          * only userfault.
557                          */
558                         write_seqcount_begin(&ctx->refile_seq);
559 
560                         /*
561                          * The fault_pending_wqh.lock prevents the uwq
562                          * to disappear from under us.
563                          *
564                          * Refile this userfault from
565                          * fault_pending_wqh to fault_wqh, it's not
566                          * pending anymore after we read it.
567                          *
568                          * Use list_del() by hand (as
569                          * userfaultfd_wake_function also uses
570                          * list_del_init() by hand) to be sure nobody
571                          * changes __remove_wait_queue() to use
572                          * list_del_init() in turn breaking the
573                          * !list_empty_careful() check in
574                          * handle_userfault(). The uwq->wq.task_list
575                          * must never be empty at any time during the
576                          * refile, or the waitqueue could disappear
577                          * from under us. The "wait_queue_head_t"
578                          * parameter of __remove_wait_queue() is unused
579                          * anyway.
580                          */
581                         list_del(&uwq->wq.task_list);
582                         __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
583 
584                         write_seqcount_end(&ctx->refile_seq);
585 
586                         /* careful to always initialize msg if ret == 0 */
587                         *msg = uwq->msg;
588                         spin_unlock(&ctx->fault_pending_wqh.lock);
589                         ret = 0;
590                         break;
591                 }
592                 spin_unlock(&ctx->fault_pending_wqh.lock);
593                 if (signal_pending(current)) {
594                         ret = -ERESTARTSYS;
595                         break;
596                 }
597                 if (no_wait) {
598                         ret = -EAGAIN;
599                         break;
600                 }
601                 spin_unlock(&ctx->fd_wqh.lock);
602                 schedule();
603                 spin_lock(&ctx->fd_wqh.lock);
604         }
605         __remove_wait_queue(&ctx->fd_wqh, &wait);
606         __set_current_state(TASK_RUNNING);
607         spin_unlock(&ctx->fd_wqh.lock);
608 
609         return ret;
610 }
611 
612 static ssize_t userfaultfd_read(struct file *file, char __user *buf,
613                                 size_t count, loff_t *ppos)
614 {
615         struct userfaultfd_ctx *ctx = file->private_data;
616         ssize_t _ret, ret = 0;
617         struct uffd_msg msg;
618         int no_wait = file->f_flags & O_NONBLOCK;
619 
620         if (ctx->state == UFFD_STATE_WAIT_API)
621                 return -EINVAL;
622 
623         for (;;) {
624                 if (count < sizeof(msg))
625                         return ret ? ret : -EINVAL;
626                 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
627                 if (_ret < 0)
628                         return ret ? ret : _ret;
629                 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
630                         return ret ? ret : -EFAULT;
631                 ret += sizeof(msg);
632                 buf += sizeof(msg);
633                 count -= sizeof(msg);
634                 /*
635                  * Allow to read more than one fault at time but only
636                  * block if waiting for the very first one.
637                  */
638                 no_wait = O_NONBLOCK;
639         }
640 }
641 
642 static void __wake_userfault(struct userfaultfd_ctx *ctx,
643                              struct userfaultfd_wake_range *range)
644 {
645         unsigned long start, end;
646 
647         start = range->start;
648         end = range->start + range->len;
649 
650         spin_lock(&ctx->fault_pending_wqh.lock);
651         /* wake all in the range and autoremove */
652         if (waitqueue_active(&ctx->fault_pending_wqh))
653                 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
654                                      range);
655         if (waitqueue_active(&ctx->fault_wqh))
656                 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
657         spin_unlock(&ctx->fault_pending_wqh.lock);
658 }
659 
660 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
661                                            struct userfaultfd_wake_range *range)
662 {
663         unsigned seq;
664         bool need_wakeup;
665 
666         /*
667          * To be sure waitqueue_active() is not reordered by the CPU
668          * before the pagetable update, use an explicit SMP memory
669          * barrier here. PT lock release or up_read(mmap_sem) still
670          * have release semantics that can allow the
671          * waitqueue_active() to be reordered before the pte update.
672          */
673         smp_mb();
674 
675         /*
676          * Use waitqueue_active because it's very frequent to
677          * change the address space atomically even if there are no
678          * userfaults yet. So we take the spinlock only when we're
679          * sure we've userfaults to wake.
680          */
681         do {
682                 seq = read_seqcount_begin(&ctx->refile_seq);
683                 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
684                         waitqueue_active(&ctx->fault_wqh);
685                 cond_resched();
686         } while (read_seqcount_retry(&ctx->refile_seq, seq));
687         if (need_wakeup)
688                 __wake_userfault(ctx, range);
689 }
690 
691 static __always_inline int validate_range(struct mm_struct *mm,
692                                           __u64 start, __u64 len)
693 {
694         __u64 task_size = mm->task_size;
695 
696         if (start & ~PAGE_MASK)
697                 return -EINVAL;
698         if (len & ~PAGE_MASK)
699                 return -EINVAL;
700         if (!len)
701                 return -EINVAL;
702         if (start < mmap_min_addr)
703                 return -EINVAL;
704         if (start >= task_size)
705                 return -EINVAL;
706         if (len > task_size - start)
707                 return -EINVAL;
708         return 0;
709 }
710 
711 static int userfaultfd_register(struct userfaultfd_ctx *ctx,
712                                 unsigned long arg)
713 {
714         struct mm_struct *mm = ctx->mm;
715         struct vm_area_struct *vma, *prev, *cur;
716         int ret;
717         struct uffdio_register uffdio_register;
718         struct uffdio_register __user *user_uffdio_register;
719         unsigned long vm_flags, new_flags;
720         bool found;
721         unsigned long start, end, vma_end;
722 
723         user_uffdio_register = (struct uffdio_register __user *) arg;
724 
725         ret = -EFAULT;
726         if (copy_from_user(&uffdio_register, user_uffdio_register,
727                            sizeof(uffdio_register)-sizeof(__u64)))
728                 goto out;
729 
730         ret = -EINVAL;
731         if (!uffdio_register.mode)
732                 goto out;
733         if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
734                                      UFFDIO_REGISTER_MODE_WP))
735                 goto out;
736         vm_flags = 0;
737         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
738                 vm_flags |= VM_UFFD_MISSING;
739         if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
740                 vm_flags |= VM_UFFD_WP;
741                 /*
742                  * FIXME: remove the below error constraint by
743                  * implementing the wprotect tracking mode.
744                  */
745                 ret = -EINVAL;
746                 goto out;
747         }
748 
749         ret = validate_range(mm, uffdio_register.range.start,
750                              uffdio_register.range.len);
751         if (ret)
752                 goto out;
753 
754         start = uffdio_register.range.start;
755         end = start + uffdio_register.range.len;
756 
757         down_write(&mm->mmap_sem);
758         vma = find_vma_prev(mm, start, &prev);
759 
760         ret = -ENOMEM;
761         if (!vma)
762                 goto out_unlock;
763 
764         /* check that there's at least one vma in the range */
765         ret = -EINVAL;
766         if (vma->vm_start >= end)
767                 goto out_unlock;
768 
769         /*
770          * Search for not compatible vmas.
771          *
772          * FIXME: this shall be relaxed later so that it doesn't fail
773          * on tmpfs backed vmas (in addition to the current allowance
774          * on anonymous vmas).
775          */
776         found = false;
777         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
778                 cond_resched();
779 
780                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
781                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
782 
783                 /* check not compatible vmas */
784                 ret = -EINVAL;
785                 if (cur->vm_ops)
786                         goto out_unlock;
787 
788                 /*
789                  * Check that this vma isn't already owned by a
790                  * different userfaultfd. We can't allow more than one
791                  * userfaultfd to own a single vma simultaneously or we
792                  * wouldn't know which one to deliver the userfaults to.
793                  */
794                 ret = -EBUSY;
795                 if (cur->vm_userfaultfd_ctx.ctx &&
796                     cur->vm_userfaultfd_ctx.ctx != ctx)
797                         goto out_unlock;
798 
799                 found = true;
800         }
801         BUG_ON(!found);
802 
803         if (vma->vm_start < start)
804                 prev = vma;
805 
806         ret = 0;
807         do {
808                 cond_resched();
809 
810                 BUG_ON(vma->vm_ops);
811                 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
812                        vma->vm_userfaultfd_ctx.ctx != ctx);
813 
814                 /*
815                  * Nothing to do: this vma is already registered into this
816                  * userfaultfd and with the right tracking mode too.
817                  */
818                 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
819                     (vma->vm_flags & vm_flags) == vm_flags)
820                         goto skip;
821 
822                 if (vma->vm_start > start)
823                         start = vma->vm_start;
824                 vma_end = min(end, vma->vm_end);
825 
826                 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
827                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
828                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
829                                  vma_policy(vma),
830                                  ((struct vm_userfaultfd_ctx){ ctx }));
831                 if (prev) {
832                         vma = prev;
833                         goto next;
834                 }
835                 if (vma->vm_start < start) {
836                         ret = split_vma(mm, vma, start, 1);
837                         if (ret)
838                                 break;
839                 }
840                 if (vma->vm_end > end) {
841                         ret = split_vma(mm, vma, end, 0);
842                         if (ret)
843                                 break;
844                 }
845         next:
846                 /*
847                  * In the vma_merge() successful mprotect-like case 8:
848                  * the next vma was merged into the current one and
849                  * the current one has not been updated yet.
850                  */
851                 vma->vm_flags = new_flags;
852                 vma->vm_userfaultfd_ctx.ctx = ctx;
853 
854         skip:
855                 prev = vma;
856                 start = vma->vm_end;
857                 vma = vma->vm_next;
858         } while (vma && vma->vm_start < end);
859 out_unlock:
860         up_write(&mm->mmap_sem);
861         if (!ret) {
862                 /*
863                  * Now that we scanned all vmas we can already tell
864                  * userland which ioctls methods are guaranteed to
865                  * succeed on this range.
866                  */
867                 if (put_user(UFFD_API_RANGE_IOCTLS,
868                              &user_uffdio_register->ioctls))
869                         ret = -EFAULT;
870         }
871 out:
872         return ret;
873 }
874 
875 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
876                                   unsigned long arg)
877 {
878         struct mm_struct *mm = ctx->mm;
879         struct vm_area_struct *vma, *prev, *cur;
880         int ret;
881         struct uffdio_range uffdio_unregister;
882         unsigned long new_flags;
883         bool found;
884         unsigned long start, end, vma_end;
885         const void __user *buf = (void __user *)arg;
886 
887         ret = -EFAULT;
888         if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
889                 goto out;
890 
891         ret = validate_range(mm, uffdio_unregister.start,
892                              uffdio_unregister.len);
893         if (ret)
894                 goto out;
895 
896         start = uffdio_unregister.start;
897         end = start + uffdio_unregister.len;
898 
899         down_write(&mm->mmap_sem);
900         vma = find_vma_prev(mm, start, &prev);
901 
902         ret = -ENOMEM;
903         if (!vma)
904                 goto out_unlock;
905 
906         /* check that there's at least one vma in the range */
907         ret = -EINVAL;
908         if (vma->vm_start >= end)
909                 goto out_unlock;
910 
911         /*
912          * Search for not compatible vmas.
913          *
914          * FIXME: this shall be relaxed later so that it doesn't fail
915          * on tmpfs backed vmas (in addition to the current allowance
916          * on anonymous vmas).
917          */
918         found = false;
919         ret = -EINVAL;
920         for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
921                 cond_resched();
922 
923                 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
924                        !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
925 
926                 /*
927                  * Check not compatible vmas, not strictly required
928                  * here as not compatible vmas cannot have an
929                  * userfaultfd_ctx registered on them, but this
930                  * provides for more strict behavior to notice
931                  * unregistration errors.
932                  */
933                 if (cur->vm_ops)
934                         goto out_unlock;
935 
936                 found = true;
937         }
938         BUG_ON(!found);
939 
940         if (vma->vm_start < start)
941                 prev = vma;
942 
943         ret = 0;
944         do {
945                 cond_resched();
946 
947                 BUG_ON(vma->vm_ops);
948 
949                 /*
950                  * Nothing to do: this vma is already registered into this
951                  * userfaultfd and with the right tracking mode too.
952                  */
953                 if (!vma->vm_userfaultfd_ctx.ctx)
954                         goto skip;
955 
956                 if (vma->vm_start > start)
957                         start = vma->vm_start;
958                 vma_end = min(end, vma->vm_end);
959 
960                 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
961                 prev = vma_merge(mm, prev, start, vma_end, new_flags,
962                                  vma->anon_vma, vma->vm_file, vma->vm_pgoff,
963                                  vma_policy(vma),
964                                  NULL_VM_UFFD_CTX);
965                 if (prev) {
966                         vma = prev;
967                         goto next;
968                 }
969                 if (vma->vm_start < start) {
970                         ret = split_vma(mm, vma, start, 1);
971                         if (ret)
972                                 break;
973                 }
974                 if (vma->vm_end > end) {
975                         ret = split_vma(mm, vma, end, 0);
976                         if (ret)
977                                 break;
978                 }
979         next:
980                 /*
981                  * In the vma_merge() successful mprotect-like case 8:
982                  * the next vma was merged into the current one and
983                  * the current one has not been updated yet.
984                  */
985                 vma->vm_flags = new_flags;
986                 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
987 
988         skip:
989                 prev = vma;
990                 start = vma->vm_end;
991                 vma = vma->vm_next;
992         } while (vma && vma->vm_start < end);
993 out_unlock:
994         up_write(&mm->mmap_sem);
995 out:
996         return ret;
997 }
998 
999 /*
1000  * userfaultfd_wake may be used in combination with the
1001  * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1002  */
1003 static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1004                             unsigned long arg)
1005 {
1006         int ret;
1007         struct uffdio_range uffdio_wake;
1008         struct userfaultfd_wake_range range;
1009         const void __user *buf = (void __user *)arg;
1010 
1011         ret = -EFAULT;
1012         if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1013                 goto out;
1014 
1015         ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1016         if (ret)
1017                 goto out;
1018 
1019         range.start = uffdio_wake.start;
1020         range.len = uffdio_wake.len;
1021 
1022         /*
1023          * len == 0 means wake all and we don't want to wake all here,
1024          * so check it again to be sure.
1025          */
1026         VM_BUG_ON(!range.len);
1027 
1028         wake_userfault(ctx, &range);
1029         ret = 0;
1030 
1031 out:
1032         return ret;
1033 }
1034 
1035 static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1036                             unsigned long arg)
1037 {
1038         __s64 ret;
1039         struct uffdio_copy uffdio_copy;
1040         struct uffdio_copy __user *user_uffdio_copy;
1041         struct userfaultfd_wake_range range;
1042 
1043         user_uffdio_copy = (struct uffdio_copy __user *) arg;
1044 
1045         ret = -EFAULT;
1046         if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1047                            /* don't copy "copy" last field */
1048                            sizeof(uffdio_copy)-sizeof(__s64)))
1049                 goto out;
1050 
1051         ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1052         if (ret)
1053                 goto out;
1054         /*
1055          * double check for wraparound just in case. copy_from_user()
1056          * will later check uffdio_copy.src + uffdio_copy.len to fit
1057          * in the userland range.
1058          */
1059         ret = -EINVAL;
1060         if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1061                 goto out;
1062         if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1063                 goto out;
1064 
1065         ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1066                            uffdio_copy.len);
1067         if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1068                 return -EFAULT;
1069         if (ret < 0)
1070                 goto out;
1071         BUG_ON(!ret);
1072         /* len == 0 would wake all */
1073         range.len = ret;
1074         if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1075                 range.start = uffdio_copy.dst;
1076                 wake_userfault(ctx, &range);
1077         }
1078         ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1079 out:
1080         return ret;
1081 }
1082 
1083 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1084                                 unsigned long arg)
1085 {
1086         __s64 ret;
1087         struct uffdio_zeropage uffdio_zeropage;
1088         struct uffdio_zeropage __user *user_uffdio_zeropage;
1089         struct userfaultfd_wake_range range;
1090 
1091         user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1092 
1093         ret = -EFAULT;
1094         if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1095                            /* don't copy "zeropage" last field */
1096                            sizeof(uffdio_zeropage)-sizeof(__s64)))
1097                 goto out;
1098 
1099         ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1100                              uffdio_zeropage.range.len);
1101         if (ret)
1102                 goto out;
1103         ret = -EINVAL;
1104         if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1105                 goto out;
1106 
1107         ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1108                              uffdio_zeropage.range.len);
1109         if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1110                 return -EFAULT;
1111         if (ret < 0)
1112                 goto out;
1113         /* len == 0 would wake all */
1114         BUG_ON(!ret);
1115         range.len = ret;
1116         if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1117                 range.start = uffdio_zeropage.range.start;
1118                 wake_userfault(ctx, &range);
1119         }
1120         ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1121 out:
1122         return ret;
1123 }
1124 
1125 /*
1126  * userland asks for a certain API version and we return which bits
1127  * and ioctl commands are implemented in this kernel for such API
1128  * version or -EINVAL if unknown.
1129  */
1130 static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1131                            unsigned long arg)
1132 {
1133         struct uffdio_api uffdio_api;
1134         void __user *buf = (void __user *)arg;
1135         int ret;
1136 
1137         ret = -EINVAL;
1138         if (ctx->state != UFFD_STATE_WAIT_API)
1139                 goto out;
1140         ret = -EFAULT;
1141         if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1142                 goto out;
1143         if (uffdio_api.api != UFFD_API || uffdio_api.features) {
1144                 memset(&uffdio_api, 0, sizeof(uffdio_api));
1145                 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1146                         goto out;
1147                 ret = -EINVAL;
1148                 goto out;
1149         }
1150         uffdio_api.features = UFFD_API_FEATURES;
1151         uffdio_api.ioctls = UFFD_API_IOCTLS;
1152         ret = -EFAULT;
1153         if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1154                 goto out;
1155         ctx->state = UFFD_STATE_RUNNING;
1156         ret = 0;
1157 out:
1158         return ret;
1159 }
1160 
1161 static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1162                               unsigned long arg)
1163 {
1164         int ret = -EINVAL;
1165         struct userfaultfd_ctx *ctx = file->private_data;
1166 
1167         if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1168                 return -EINVAL;
1169 
1170         switch(cmd) {
1171         case UFFDIO_API:
1172                 ret = userfaultfd_api(ctx, arg);
1173                 break;
1174         case UFFDIO_REGISTER:
1175                 ret = userfaultfd_register(ctx, arg);
1176                 break;
1177         case UFFDIO_UNREGISTER:
1178                 ret = userfaultfd_unregister(ctx, arg);
1179                 break;
1180         case UFFDIO_WAKE:
1181                 ret = userfaultfd_wake(ctx, arg);
1182                 break;
1183         case UFFDIO_COPY:
1184                 ret = userfaultfd_copy(ctx, arg);
1185                 break;
1186         case UFFDIO_ZEROPAGE:
1187                 ret = userfaultfd_zeropage(ctx, arg);
1188                 break;
1189         }
1190         return ret;
1191 }
1192 
1193 #ifdef CONFIG_PROC_FS
1194 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1195 {
1196         struct userfaultfd_ctx *ctx = f->private_data;
1197         wait_queue_t *wq;
1198         struct userfaultfd_wait_queue *uwq;
1199         unsigned long pending = 0, total = 0;
1200 
1201         spin_lock(&ctx->fault_pending_wqh.lock);
1202         list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) {
1203                 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1204                 pending++;
1205                 total++;
1206         }
1207         list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) {
1208                 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1209                 total++;
1210         }
1211         spin_unlock(&ctx->fault_pending_wqh.lock);
1212 
1213         /*
1214          * If more protocols will be added, there will be all shown
1215          * separated by a space. Like this:
1216          *      protocols: aa:... bb:...
1217          */
1218         seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1219                    pending, total, UFFD_API, UFFD_API_FEATURES,
1220                    UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1221 }
1222 #endif
1223 
1224 static const struct file_operations userfaultfd_fops = {
1225 #ifdef CONFIG_PROC_FS
1226         .show_fdinfo    = userfaultfd_show_fdinfo,
1227 #endif
1228         .release        = userfaultfd_release,
1229         .poll           = userfaultfd_poll,
1230         .read           = userfaultfd_read,
1231         .unlocked_ioctl = userfaultfd_ioctl,
1232         .compat_ioctl   = userfaultfd_ioctl,
1233         .llseek         = noop_llseek,
1234 };
1235 
1236 static void init_once_userfaultfd_ctx(void *mem)
1237 {
1238         struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1239 
1240         init_waitqueue_head(&ctx->fault_pending_wqh);
1241         init_waitqueue_head(&ctx->fault_wqh);
1242         init_waitqueue_head(&ctx->fd_wqh);
1243         seqcount_init(&ctx->refile_seq);
1244 }
1245 
1246 /**
1247  * userfaultfd_file_create - Creates an userfaultfd file pointer.
1248  * @flags: Flags for the userfaultfd file.
1249  *
1250  * This function creates an userfaultfd file pointer, w/out installing
1251  * it into the fd table. This is useful when the userfaultfd file is
1252  * used during the initialization of data structures that require
1253  * extra setup after the userfaultfd creation. So the userfaultfd
1254  * creation is split into the file pointer creation phase, and the
1255  * file descriptor installation phase.  In this way races with
1256  * userspace closing the newly installed file descriptor can be
1257  * avoided.  Returns an userfaultfd file pointer, or a proper error
1258  * pointer.
1259  */
1260 static struct file *userfaultfd_file_create(int flags)
1261 {
1262         struct file *file;
1263         struct userfaultfd_ctx *ctx;
1264 
1265         BUG_ON(!current->mm);
1266 
1267         /* Check the UFFD_* constants for consistency.  */
1268         BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1269         BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1270 
1271         file = ERR_PTR(-EINVAL);
1272         if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1273                 goto out;
1274 
1275         file = ERR_PTR(-ENOMEM);
1276         ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1277         if (!ctx)
1278                 goto out;
1279 
1280         atomic_set(&ctx->refcount, 1);
1281         ctx->flags = flags;
1282         ctx->state = UFFD_STATE_WAIT_API;
1283         ctx->released = false;
1284         ctx->mm = current->mm;
1285         /* prevent the mm struct to be freed */
1286         atomic_inc(&ctx->mm->mm_users);
1287 
1288         file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1289                                   O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1290         if (IS_ERR(file)) {
1291                 mmput(ctx->mm);
1292                 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1293         }
1294 out:
1295         return file;
1296 }
1297 
1298 SYSCALL_DEFINE1(userfaultfd, int, flags)
1299 {
1300         int fd, error;
1301         struct file *file;
1302 
1303         error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1304         if (error < 0)
1305                 return error;
1306         fd = error;
1307 
1308         file = userfaultfd_file_create(flags);
1309         if (IS_ERR(file)) {
1310                 error = PTR_ERR(file);
1311                 goto err_put_unused_fd;
1312         }
1313         fd_install(fd, file);
1314 
1315         return fd;
1316 
1317 err_put_unused_fd:
1318         put_unused_fd(fd);
1319 
1320         return error;
1321 }
1322 
1323 static int __init userfaultfd_init(void)
1324 {
1325         userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1326                                                 sizeof(struct userfaultfd_ctx),
1327                                                 0,
1328                                                 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1329                                                 init_once_userfaultfd_ctx);
1330         return 0;
1331 }
1332 __initcall(userfaultfd_init);
1333 

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