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