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 mmdrop(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_fault *vmf, unsigned long reason) 261 { 262 struct mm_struct *mm = vmf->vma->vm_mm; 263 struct userfaultfd_ctx *ctx; 264 struct userfaultfd_wait_queue uwq; 265 int ret; 266 bool must_wait, return_to_userland; 267 268 BUG_ON(!rwsem_is_locked(&mm->mmap_sem)); 269 270 ret = VM_FAULT_SIGBUS; 271 ctx = vmf->vma->vm_userfaultfd_ctx.ctx; 272 if (!ctx) 273 goto out; 274 275 BUG_ON(ctx->mm != mm); 276 277 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP)); 278 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP)); 279 280 /* 281 * If it's already released don't get it. This avoids to loop 282 * in __get_user_pages if userfaultfd_release waits on the 283 * caller of handle_userfault to release the mmap_sem. 284 */ 285 if (unlikely(ACCESS_ONCE(ctx->released))) 286 goto out; 287 288 /* 289 * We don't do userfault handling for the final child pid update. 290 */ 291 if (current->flags & PF_EXITING) 292 goto out; 293 294 /* 295 * Check that we can return VM_FAULT_RETRY. 296 * 297 * NOTE: it should become possible to return VM_FAULT_RETRY 298 * even if FAULT_FLAG_TRIED is set without leading to gup() 299 * -EBUSY failures, if the userfaultfd is to be extended for 300 * VM_UFFD_WP tracking and we intend to arm the userfault 301 * without first stopping userland access to the memory. For 302 * VM_UFFD_MISSING userfaults this is enough for now. 303 */ 304 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) { 305 /* 306 * Validate the invariant that nowait must allow retry 307 * to be sure not to return SIGBUS erroneously on 308 * nowait invocations. 309 */ 310 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT); 311 #ifdef CONFIG_DEBUG_VM 312 if (printk_ratelimit()) { 313 printk(KERN_WARNING 314 "FAULT_FLAG_ALLOW_RETRY missing %x\n", 315 vmf->flags); 316 dump_stack(); 317 } 318 #endif 319 goto out; 320 } 321 322 /* 323 * Handle nowait, not much to do other than tell it to retry 324 * and wait. 325 */ 326 ret = VM_FAULT_RETRY; 327 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) 328 goto out; 329 330 /* take the reference before dropping the mmap_sem */ 331 userfaultfd_ctx_get(ctx); 332 333 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); 334 uwq.wq.private = current; 335 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason); 336 uwq.ctx = ctx; 337 338 return_to_userland = 339 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) == 340 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE); 341 342 spin_lock(&ctx->fault_pending_wqh.lock); 343 /* 344 * After the __add_wait_queue the uwq is visible to userland 345 * through poll/read(). 346 */ 347 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq); 348 /* 349 * The smp_mb() after __set_current_state prevents the reads 350 * following the spin_unlock to happen before the list_add in 351 * __add_wait_queue. 352 */ 353 set_current_state(return_to_userland ? TASK_INTERRUPTIBLE : 354 TASK_KILLABLE); 355 spin_unlock(&ctx->fault_pending_wqh.lock); 356 357 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags, 358 reason); 359 up_read(&mm->mmap_sem); 360 361 if (likely(must_wait && !ACCESS_ONCE(ctx->released) && 362 (return_to_userland ? !signal_pending(current) : 363 !fatal_signal_pending(current)))) { 364 wake_up_poll(&ctx->fd_wqh, POLLIN); 365 schedule(); 366 ret |= VM_FAULT_MAJOR; 367 } 368 369 __set_current_state(TASK_RUNNING); 370 371 if (return_to_userland) { 372 if (signal_pending(current) && 373 !fatal_signal_pending(current)) { 374 /* 375 * If we got a SIGSTOP or SIGCONT and this is 376 * a normal userland page fault, just let 377 * userland return so the signal will be 378 * handled and gdb debugging works. The page 379 * fault code immediately after we return from 380 * this function is going to release the 381 * mmap_sem and it's not depending on it 382 * (unlike gup would if we were not to return 383 * VM_FAULT_RETRY). 384 * 385 * If a fatal signal is pending we still take 386 * the streamlined VM_FAULT_RETRY failure path 387 * and there's no need to retake the mmap_sem 388 * in such case. 389 */ 390 down_read(&mm->mmap_sem); 391 ret = 0; 392 } 393 } 394 395 /* 396 * Here we race with the list_del; list_add in 397 * userfaultfd_ctx_read(), however because we don't ever run 398 * list_del_init() to refile across the two lists, the prev 399 * and next pointers will never point to self. list_add also 400 * would never let any of the two pointers to point to 401 * self. So list_empty_careful won't risk to see both pointers 402 * pointing to self at any time during the list refile. The 403 * only case where list_del_init() is called is the full 404 * removal in the wake function and there we don't re-list_add 405 * and it's fine not to block on the spinlock. The uwq on this 406 * kernel stack can be released after the list_del_init. 407 */ 408 if (!list_empty_careful(&uwq.wq.task_list)) { 409 spin_lock(&ctx->fault_pending_wqh.lock); 410 /* 411 * No need of list_del_init(), the uwq on the stack 412 * will be freed shortly anyway. 413 */ 414 list_del(&uwq.wq.task_list); 415 spin_unlock(&ctx->fault_pending_wqh.lock); 416 } 417 418 /* 419 * ctx may go away after this if the userfault pseudo fd is 420 * already released. 421 */ 422 userfaultfd_ctx_put(ctx); 423 424 out: 425 return ret; 426 } 427 428 static int userfaultfd_release(struct inode *inode, struct file *file) 429 { 430 struct userfaultfd_ctx *ctx = file->private_data; 431 struct mm_struct *mm = ctx->mm; 432 struct vm_area_struct *vma, *prev; 433 /* len == 0 means wake all */ 434 struct userfaultfd_wake_range range = { .len = 0, }; 435 unsigned long new_flags; 436 437 ACCESS_ONCE(ctx->released) = true; 438 439 if (!mmget_not_zero(mm)) 440 goto wakeup; 441 442 /* 443 * Flush page faults out of all CPUs. NOTE: all page faults 444 * must be retried without returning VM_FAULT_SIGBUS if 445 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx 446 * changes while handle_userfault released the mmap_sem. So 447 * it's critical that released is set to true (above), before 448 * taking the mmap_sem for writing. 449 */ 450 down_write(&mm->mmap_sem); 451 prev = NULL; 452 for (vma = mm->mmap; vma; vma = vma->vm_next) { 453 cond_resched(); 454 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^ 455 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 456 if (vma->vm_userfaultfd_ctx.ctx != ctx) { 457 prev = vma; 458 continue; 459 } 460 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 461 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end, 462 new_flags, vma->anon_vma, 463 vma->vm_file, vma->vm_pgoff, 464 vma_policy(vma), 465 NULL_VM_UFFD_CTX); 466 if (prev) 467 vma = prev; 468 else 469 prev = vma; 470 vma->vm_flags = new_flags; 471 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 472 } 473 up_write(&mm->mmap_sem); 474 mmput(mm); 475 wakeup: 476 /* 477 * After no new page faults can wait on this fault_*wqh, flush 478 * the last page faults that may have been already waiting on 479 * the fault_*wqh. 480 */ 481 spin_lock(&ctx->fault_pending_wqh.lock); 482 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range); 483 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range); 484 spin_unlock(&ctx->fault_pending_wqh.lock); 485 486 wake_up_poll(&ctx->fd_wqh, POLLHUP); 487 userfaultfd_ctx_put(ctx); 488 return 0; 489 } 490 491 /* fault_pending_wqh.lock must be hold by the caller */ 492 static inline struct userfaultfd_wait_queue *find_userfault( 493 struct userfaultfd_ctx *ctx) 494 { 495 wait_queue_t *wq; 496 struct userfaultfd_wait_queue *uwq; 497 498 VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock)); 499 500 uwq = NULL; 501 if (!waitqueue_active(&ctx->fault_pending_wqh)) 502 goto out; 503 /* walk in reverse to provide FIFO behavior to read userfaults */ 504 wq = list_last_entry(&ctx->fault_pending_wqh.task_list, 505 typeof(*wq), task_list); 506 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 507 out: 508 return uwq; 509 } 510 511 static unsigned int userfaultfd_poll(struct file *file, poll_table *wait) 512 { 513 struct userfaultfd_ctx *ctx = file->private_data; 514 unsigned int ret; 515 516 poll_wait(file, &ctx->fd_wqh, wait); 517 518 switch (ctx->state) { 519 case UFFD_STATE_WAIT_API: 520 return POLLERR; 521 case UFFD_STATE_RUNNING: 522 /* 523 * poll() never guarantees that read won't block. 524 * userfaults can be waken before they're read(). 525 */ 526 if (unlikely(!(file->f_flags & O_NONBLOCK))) 527 return POLLERR; 528 /* 529 * lockless access to see if there are pending faults 530 * __pollwait last action is the add_wait_queue but 531 * the spin_unlock would allow the waitqueue_active to 532 * pass above the actual list_add inside 533 * add_wait_queue critical section. So use a full 534 * memory barrier to serialize the list_add write of 535 * add_wait_queue() with the waitqueue_active read 536 * below. 537 */ 538 ret = 0; 539 smp_mb(); 540 if (waitqueue_active(&ctx->fault_pending_wqh)) 541 ret = POLLIN; 542 return ret; 543 default: 544 BUG(); 545 } 546 } 547 548 static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait, 549 struct uffd_msg *msg) 550 { 551 ssize_t ret; 552 DECLARE_WAITQUEUE(wait, current); 553 struct userfaultfd_wait_queue *uwq; 554 555 /* always take the fd_wqh lock before the fault_pending_wqh lock */ 556 spin_lock(&ctx->fd_wqh.lock); 557 __add_wait_queue(&ctx->fd_wqh, &wait); 558 for (;;) { 559 set_current_state(TASK_INTERRUPTIBLE); 560 spin_lock(&ctx->fault_pending_wqh.lock); 561 uwq = find_userfault(ctx); 562 if (uwq) { 563 /* 564 * Use a seqcount to repeat the lockless check 565 * in wake_userfault() to avoid missing 566 * wakeups because during the refile both 567 * waitqueue could become empty if this is the 568 * only userfault. 569 */ 570 write_seqcount_begin(&ctx->refile_seq); 571 572 /* 573 * The fault_pending_wqh.lock prevents the uwq 574 * to disappear from under us. 575 * 576 * Refile this userfault from 577 * fault_pending_wqh to fault_wqh, it's not 578 * pending anymore after we read it. 579 * 580 * Use list_del() by hand (as 581 * userfaultfd_wake_function also uses 582 * list_del_init() by hand) to be sure nobody 583 * changes __remove_wait_queue() to use 584 * list_del_init() in turn breaking the 585 * !list_empty_careful() check in 586 * handle_userfault(). The uwq->wq.task_list 587 * must never be empty at any time during the 588 * refile, or the waitqueue could disappear 589 * from under us. The "wait_queue_head_t" 590 * parameter of __remove_wait_queue() is unused 591 * anyway. 592 */ 593 list_del(&uwq->wq.task_list); 594 __add_wait_queue(&ctx->fault_wqh, &uwq->wq); 595 596 write_seqcount_end(&ctx->refile_seq); 597 598 /* careful to always initialize msg if ret == 0 */ 599 *msg = uwq->msg; 600 spin_unlock(&ctx->fault_pending_wqh.lock); 601 ret = 0; 602 break; 603 } 604 spin_unlock(&ctx->fault_pending_wqh.lock); 605 if (signal_pending(current)) { 606 ret = -ERESTARTSYS; 607 break; 608 } 609 if (no_wait) { 610 ret = -EAGAIN; 611 break; 612 } 613 spin_unlock(&ctx->fd_wqh.lock); 614 schedule(); 615 spin_lock(&ctx->fd_wqh.lock); 616 } 617 __remove_wait_queue(&ctx->fd_wqh, &wait); 618 __set_current_state(TASK_RUNNING); 619 spin_unlock(&ctx->fd_wqh.lock); 620 621 return ret; 622 } 623 624 static ssize_t userfaultfd_read(struct file *file, char __user *buf, 625 size_t count, loff_t *ppos) 626 { 627 struct userfaultfd_ctx *ctx = file->private_data; 628 ssize_t _ret, ret = 0; 629 struct uffd_msg msg; 630 int no_wait = file->f_flags & O_NONBLOCK; 631 632 if (ctx->state == UFFD_STATE_WAIT_API) 633 return -EINVAL; 634 635 for (;;) { 636 if (count < sizeof(msg)) 637 return ret ? ret : -EINVAL; 638 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg); 639 if (_ret < 0) 640 return ret ? ret : _ret; 641 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg))) 642 return ret ? ret : -EFAULT; 643 ret += sizeof(msg); 644 buf += sizeof(msg); 645 count -= sizeof(msg); 646 /* 647 * Allow to read more than one fault at time but only 648 * block if waiting for the very first one. 649 */ 650 no_wait = O_NONBLOCK; 651 } 652 } 653 654 static void __wake_userfault(struct userfaultfd_ctx *ctx, 655 struct userfaultfd_wake_range *range) 656 { 657 unsigned long start, end; 658 659 start = range->start; 660 end = range->start + range->len; 661 662 spin_lock(&ctx->fault_pending_wqh.lock); 663 /* wake all in the range and autoremove */ 664 if (waitqueue_active(&ctx->fault_pending_wqh)) 665 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, 666 range); 667 if (waitqueue_active(&ctx->fault_wqh)) 668 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range); 669 spin_unlock(&ctx->fault_pending_wqh.lock); 670 } 671 672 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx, 673 struct userfaultfd_wake_range *range) 674 { 675 unsigned seq; 676 bool need_wakeup; 677 678 /* 679 * To be sure waitqueue_active() is not reordered by the CPU 680 * before the pagetable update, use an explicit SMP memory 681 * barrier here. PT lock release or up_read(mmap_sem) still 682 * have release semantics that can allow the 683 * waitqueue_active() to be reordered before the pte update. 684 */ 685 smp_mb(); 686 687 /* 688 * Use waitqueue_active because it's very frequent to 689 * change the address space atomically even if there are no 690 * userfaults yet. So we take the spinlock only when we're 691 * sure we've userfaults to wake. 692 */ 693 do { 694 seq = read_seqcount_begin(&ctx->refile_seq); 695 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) || 696 waitqueue_active(&ctx->fault_wqh); 697 cond_resched(); 698 } while (read_seqcount_retry(&ctx->refile_seq, seq)); 699 if (need_wakeup) 700 __wake_userfault(ctx, range); 701 } 702 703 static __always_inline int validate_range(struct mm_struct *mm, 704 __u64 start, __u64 len) 705 { 706 __u64 task_size = mm->task_size; 707 708 if (start & ~PAGE_MASK) 709 return -EINVAL; 710 if (len & ~PAGE_MASK) 711 return -EINVAL; 712 if (!len) 713 return -EINVAL; 714 if (start < mmap_min_addr) 715 return -EINVAL; 716 if (start >= task_size) 717 return -EINVAL; 718 if (len > task_size - start) 719 return -EINVAL; 720 return 0; 721 } 722 723 static int userfaultfd_register(struct userfaultfd_ctx *ctx, 724 unsigned long arg) 725 { 726 struct mm_struct *mm = ctx->mm; 727 struct vm_area_struct *vma, *prev, *cur; 728 int ret; 729 struct uffdio_register uffdio_register; 730 struct uffdio_register __user *user_uffdio_register; 731 unsigned long vm_flags, new_flags; 732 bool found; 733 unsigned long start, end, vma_end; 734 735 user_uffdio_register = (struct uffdio_register __user *) arg; 736 737 ret = -EFAULT; 738 if (copy_from_user(&uffdio_register, user_uffdio_register, 739 sizeof(uffdio_register)-sizeof(__u64))) 740 goto out; 741 742 ret = -EINVAL; 743 if (!uffdio_register.mode) 744 goto out; 745 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING| 746 UFFDIO_REGISTER_MODE_WP)) 747 goto out; 748 vm_flags = 0; 749 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING) 750 vm_flags |= VM_UFFD_MISSING; 751 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) { 752 vm_flags |= VM_UFFD_WP; 753 /* 754 * FIXME: remove the below error constraint by 755 * implementing the wprotect tracking mode. 756 */ 757 ret = -EINVAL; 758 goto out; 759 } 760 761 ret = validate_range(mm, uffdio_register.range.start, 762 uffdio_register.range.len); 763 if (ret) 764 goto out; 765 766 start = uffdio_register.range.start; 767 end = start + uffdio_register.range.len; 768 769 ret = -ENOMEM; 770 if (!mmget_not_zero(mm)) 771 goto out; 772 773 down_write(&mm->mmap_sem); 774 vma = find_vma_prev(mm, start, &prev); 775 if (!vma) 776 goto out_unlock; 777 778 /* check that there's at least one vma in the range */ 779 ret = -EINVAL; 780 if (vma->vm_start >= end) 781 goto out_unlock; 782 783 /* 784 * Search for not compatible vmas. 785 * 786 * FIXME: this shall be relaxed later so that it doesn't fail 787 * on tmpfs backed vmas (in addition to the current allowance 788 * on anonymous vmas). 789 */ 790 found = false; 791 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 792 cond_resched(); 793 794 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 795 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 796 797 /* check not compatible vmas */ 798 ret = -EINVAL; 799 if (cur->vm_ops) 800 goto out_unlock; 801 802 /* 803 * Check that this vma isn't already owned by a 804 * different userfaultfd. We can't allow more than one 805 * userfaultfd to own a single vma simultaneously or we 806 * wouldn't know which one to deliver the userfaults to. 807 */ 808 ret = -EBUSY; 809 if (cur->vm_userfaultfd_ctx.ctx && 810 cur->vm_userfaultfd_ctx.ctx != ctx) 811 goto out_unlock; 812 813 found = true; 814 } 815 BUG_ON(!found); 816 817 if (vma->vm_start < start) 818 prev = vma; 819 820 ret = 0; 821 do { 822 cond_resched(); 823 824 BUG_ON(vma->vm_ops); 825 BUG_ON(vma->vm_userfaultfd_ctx.ctx && 826 vma->vm_userfaultfd_ctx.ctx != ctx); 827 828 /* 829 * Nothing to do: this vma is already registered into this 830 * userfaultfd and with the right tracking mode too. 831 */ 832 if (vma->vm_userfaultfd_ctx.ctx == ctx && 833 (vma->vm_flags & vm_flags) == vm_flags) 834 goto skip; 835 836 if (vma->vm_start > start) 837 start = vma->vm_start; 838 vma_end = min(end, vma->vm_end); 839 840 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags; 841 prev = vma_merge(mm, prev, start, vma_end, new_flags, 842 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 843 vma_policy(vma), 844 ((struct vm_userfaultfd_ctx){ ctx })); 845 if (prev) { 846 vma = prev; 847 goto next; 848 } 849 if (vma->vm_start < start) { 850 ret = split_vma(mm, vma, start, 1); 851 if (ret) 852 break; 853 } 854 if (vma->vm_end > end) { 855 ret = split_vma(mm, vma, end, 0); 856 if (ret) 857 break; 858 } 859 next: 860 /* 861 * In the vma_merge() successful mprotect-like case 8: 862 * the next vma was merged into the current one and 863 * the current one has not been updated yet. 864 */ 865 vma->vm_flags = new_flags; 866 vma->vm_userfaultfd_ctx.ctx = ctx; 867 868 skip: 869 prev = vma; 870 start = vma->vm_end; 871 vma = vma->vm_next; 872 } while (vma && vma->vm_start < end); 873 out_unlock: 874 up_write(&mm->mmap_sem); 875 mmput(mm); 876 if (!ret) { 877 /* 878 * Now that we scanned all vmas we can already tell 879 * userland which ioctls methods are guaranteed to 880 * succeed on this range. 881 */ 882 if (put_user(UFFD_API_RANGE_IOCTLS, 883 &user_uffdio_register->ioctls)) 884 ret = -EFAULT; 885 } 886 out: 887 return ret; 888 } 889 890 static int userfaultfd_unregister(struct userfaultfd_ctx *ctx, 891 unsigned long arg) 892 { 893 struct mm_struct *mm = ctx->mm; 894 struct vm_area_struct *vma, *prev, *cur; 895 int ret; 896 struct uffdio_range uffdio_unregister; 897 unsigned long new_flags; 898 bool found; 899 unsigned long start, end, vma_end; 900 const void __user *buf = (void __user *)arg; 901 902 ret = -EFAULT; 903 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister))) 904 goto out; 905 906 ret = validate_range(mm, uffdio_unregister.start, 907 uffdio_unregister.len); 908 if (ret) 909 goto out; 910 911 start = uffdio_unregister.start; 912 end = start + uffdio_unregister.len; 913 914 ret = -ENOMEM; 915 if (!mmget_not_zero(mm)) 916 goto out; 917 918 down_write(&mm->mmap_sem); 919 vma = find_vma_prev(mm, start, &prev); 920 if (!vma) 921 goto out_unlock; 922 923 /* check that there's at least one vma in the range */ 924 ret = -EINVAL; 925 if (vma->vm_start >= end) 926 goto out_unlock; 927 928 /* 929 * Search for not compatible vmas. 930 * 931 * FIXME: this shall be relaxed later so that it doesn't fail 932 * on tmpfs backed vmas (in addition to the current allowance 933 * on anonymous vmas). 934 */ 935 found = false; 936 ret = -EINVAL; 937 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) { 938 cond_resched(); 939 940 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^ 941 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP))); 942 943 /* 944 * Check not compatible vmas, not strictly required 945 * here as not compatible vmas cannot have an 946 * userfaultfd_ctx registered on them, but this 947 * provides for more strict behavior to notice 948 * unregistration errors. 949 */ 950 if (cur->vm_ops) 951 goto out_unlock; 952 953 found = true; 954 } 955 BUG_ON(!found); 956 957 if (vma->vm_start < start) 958 prev = vma; 959 960 ret = 0; 961 do { 962 cond_resched(); 963 964 BUG_ON(vma->vm_ops); 965 966 /* 967 * Nothing to do: this vma is already registered into this 968 * userfaultfd and with the right tracking mode too. 969 */ 970 if (!vma->vm_userfaultfd_ctx.ctx) 971 goto skip; 972 973 if (vma->vm_start > start) 974 start = vma->vm_start; 975 vma_end = min(end, vma->vm_end); 976 977 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP); 978 prev = vma_merge(mm, prev, start, vma_end, new_flags, 979 vma->anon_vma, vma->vm_file, vma->vm_pgoff, 980 vma_policy(vma), 981 NULL_VM_UFFD_CTX); 982 if (prev) { 983 vma = prev; 984 goto next; 985 } 986 if (vma->vm_start < start) { 987 ret = split_vma(mm, vma, start, 1); 988 if (ret) 989 break; 990 } 991 if (vma->vm_end > end) { 992 ret = split_vma(mm, vma, end, 0); 993 if (ret) 994 break; 995 } 996 next: 997 /* 998 * In the vma_merge() successful mprotect-like case 8: 999 * the next vma was merged into the current one and 1000 * the current one has not been updated yet. 1001 */ 1002 vma->vm_flags = new_flags; 1003 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX; 1004 1005 skip: 1006 prev = vma; 1007 start = vma->vm_end; 1008 vma = vma->vm_next; 1009 } while (vma && vma->vm_start < end); 1010 out_unlock: 1011 up_write(&mm->mmap_sem); 1012 mmput(mm); 1013 out: 1014 return ret; 1015 } 1016 1017 /* 1018 * userfaultfd_wake may be used in combination with the 1019 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches. 1020 */ 1021 static int userfaultfd_wake(struct userfaultfd_ctx *ctx, 1022 unsigned long arg) 1023 { 1024 int ret; 1025 struct uffdio_range uffdio_wake; 1026 struct userfaultfd_wake_range range; 1027 const void __user *buf = (void __user *)arg; 1028 1029 ret = -EFAULT; 1030 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake))) 1031 goto out; 1032 1033 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len); 1034 if (ret) 1035 goto out; 1036 1037 range.start = uffdio_wake.start; 1038 range.len = uffdio_wake.len; 1039 1040 /* 1041 * len == 0 means wake all and we don't want to wake all here, 1042 * so check it again to be sure. 1043 */ 1044 VM_BUG_ON(!range.len); 1045 1046 wake_userfault(ctx, &range); 1047 ret = 0; 1048 1049 out: 1050 return ret; 1051 } 1052 1053 static int userfaultfd_copy(struct userfaultfd_ctx *ctx, 1054 unsigned long arg) 1055 { 1056 __s64 ret; 1057 struct uffdio_copy uffdio_copy; 1058 struct uffdio_copy __user *user_uffdio_copy; 1059 struct userfaultfd_wake_range range; 1060 1061 user_uffdio_copy = (struct uffdio_copy __user *) arg; 1062 1063 ret = -EFAULT; 1064 if (copy_from_user(&uffdio_copy, user_uffdio_copy, 1065 /* don't copy "copy" last field */ 1066 sizeof(uffdio_copy)-sizeof(__s64))) 1067 goto out; 1068 1069 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len); 1070 if (ret) 1071 goto out; 1072 /* 1073 * double check for wraparound just in case. copy_from_user() 1074 * will later check uffdio_copy.src + uffdio_copy.len to fit 1075 * in the userland range. 1076 */ 1077 ret = -EINVAL; 1078 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src) 1079 goto out; 1080 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE) 1081 goto out; 1082 if (mmget_not_zero(ctx->mm)) { 1083 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src, 1084 uffdio_copy.len); 1085 mmput(ctx->mm); 1086 } 1087 if (unlikely(put_user(ret, &user_uffdio_copy->copy))) 1088 return -EFAULT; 1089 if (ret < 0) 1090 goto out; 1091 BUG_ON(!ret); 1092 /* len == 0 would wake all */ 1093 range.len = ret; 1094 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) { 1095 range.start = uffdio_copy.dst; 1096 wake_userfault(ctx, &range); 1097 } 1098 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN; 1099 out: 1100 return ret; 1101 } 1102 1103 static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx, 1104 unsigned long arg) 1105 { 1106 __s64 ret; 1107 struct uffdio_zeropage uffdio_zeropage; 1108 struct uffdio_zeropage __user *user_uffdio_zeropage; 1109 struct userfaultfd_wake_range range; 1110 1111 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg; 1112 1113 ret = -EFAULT; 1114 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage, 1115 /* don't copy "zeropage" last field */ 1116 sizeof(uffdio_zeropage)-sizeof(__s64))) 1117 goto out; 1118 1119 ret = validate_range(ctx->mm, uffdio_zeropage.range.start, 1120 uffdio_zeropage.range.len); 1121 if (ret) 1122 goto out; 1123 ret = -EINVAL; 1124 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE) 1125 goto out; 1126 1127 if (mmget_not_zero(ctx->mm)) { 1128 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start, 1129 uffdio_zeropage.range.len); 1130 mmput(ctx->mm); 1131 } 1132 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage))) 1133 return -EFAULT; 1134 if (ret < 0) 1135 goto out; 1136 /* len == 0 would wake all */ 1137 BUG_ON(!ret); 1138 range.len = ret; 1139 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) { 1140 range.start = uffdio_zeropage.range.start; 1141 wake_userfault(ctx, &range); 1142 } 1143 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN; 1144 out: 1145 return ret; 1146 } 1147 1148 /* 1149 * userland asks for a certain API version and we return which bits 1150 * and ioctl commands are implemented in this kernel for such API 1151 * version or -EINVAL if unknown. 1152 */ 1153 static int userfaultfd_api(struct userfaultfd_ctx *ctx, 1154 unsigned long arg) 1155 { 1156 struct uffdio_api uffdio_api; 1157 void __user *buf = (void __user *)arg; 1158 int ret; 1159 1160 ret = -EINVAL; 1161 if (ctx->state != UFFD_STATE_WAIT_API) 1162 goto out; 1163 ret = -EFAULT; 1164 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api))) 1165 goto out; 1166 if (uffdio_api.api != UFFD_API || uffdio_api.features) { 1167 memset(&uffdio_api, 0, sizeof(uffdio_api)); 1168 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1169 goto out; 1170 ret = -EINVAL; 1171 goto out; 1172 } 1173 uffdio_api.features = UFFD_API_FEATURES; 1174 uffdio_api.ioctls = UFFD_API_IOCTLS; 1175 ret = -EFAULT; 1176 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api))) 1177 goto out; 1178 ctx->state = UFFD_STATE_RUNNING; 1179 ret = 0; 1180 out: 1181 return ret; 1182 } 1183 1184 static long userfaultfd_ioctl(struct file *file, unsigned cmd, 1185 unsigned long arg) 1186 { 1187 int ret = -EINVAL; 1188 struct userfaultfd_ctx *ctx = file->private_data; 1189 1190 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API) 1191 return -EINVAL; 1192 1193 switch(cmd) { 1194 case UFFDIO_API: 1195 ret = userfaultfd_api(ctx, arg); 1196 break; 1197 case UFFDIO_REGISTER: 1198 ret = userfaultfd_register(ctx, arg); 1199 break; 1200 case UFFDIO_UNREGISTER: 1201 ret = userfaultfd_unregister(ctx, arg); 1202 break; 1203 case UFFDIO_WAKE: 1204 ret = userfaultfd_wake(ctx, arg); 1205 break; 1206 case UFFDIO_COPY: 1207 ret = userfaultfd_copy(ctx, arg); 1208 break; 1209 case UFFDIO_ZEROPAGE: 1210 ret = userfaultfd_zeropage(ctx, arg); 1211 break; 1212 } 1213 return ret; 1214 } 1215 1216 #ifdef CONFIG_PROC_FS 1217 static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f) 1218 { 1219 struct userfaultfd_ctx *ctx = f->private_data; 1220 wait_queue_t *wq; 1221 struct userfaultfd_wait_queue *uwq; 1222 unsigned long pending = 0, total = 0; 1223 1224 spin_lock(&ctx->fault_pending_wqh.lock); 1225 list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) { 1226 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1227 pending++; 1228 total++; 1229 } 1230 list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) { 1231 uwq = container_of(wq, struct userfaultfd_wait_queue, wq); 1232 total++; 1233 } 1234 spin_unlock(&ctx->fault_pending_wqh.lock); 1235 1236 /* 1237 * If more protocols will be added, there will be all shown 1238 * separated by a space. Like this: 1239 * protocols: aa:... bb:... 1240 */ 1241 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n", 1242 pending, total, UFFD_API, UFFD_API_FEATURES, 1243 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS); 1244 } 1245 #endif 1246 1247 static const struct file_operations userfaultfd_fops = { 1248 #ifdef CONFIG_PROC_FS 1249 .show_fdinfo = userfaultfd_show_fdinfo, 1250 #endif 1251 .release = userfaultfd_release, 1252 .poll = userfaultfd_poll, 1253 .read = userfaultfd_read, 1254 .unlocked_ioctl = userfaultfd_ioctl, 1255 .compat_ioctl = userfaultfd_ioctl, 1256 .llseek = noop_llseek, 1257 }; 1258 1259 static void init_once_userfaultfd_ctx(void *mem) 1260 { 1261 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem; 1262 1263 init_waitqueue_head(&ctx->fault_pending_wqh); 1264 init_waitqueue_head(&ctx->fault_wqh); 1265 init_waitqueue_head(&ctx->fd_wqh); 1266 seqcount_init(&ctx->refile_seq); 1267 } 1268 1269 /** 1270 * userfaultfd_file_create - Creates an userfaultfd file pointer. 1271 * @flags: Flags for the userfaultfd file. 1272 * 1273 * This function creates an userfaultfd file pointer, w/out installing 1274 * it into the fd table. This is useful when the userfaultfd file is 1275 * used during the initialization of data structures that require 1276 * extra setup after the userfaultfd creation. So the userfaultfd 1277 * creation is split into the file pointer creation phase, and the 1278 * file descriptor installation phase. In this way races with 1279 * userspace closing the newly installed file descriptor can be 1280 * avoided. Returns an userfaultfd file pointer, or a proper error 1281 * pointer. 1282 */ 1283 static struct file *userfaultfd_file_create(int flags) 1284 { 1285 struct file *file; 1286 struct userfaultfd_ctx *ctx; 1287 1288 BUG_ON(!current->mm); 1289 1290 /* Check the UFFD_* constants for consistency. */ 1291 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC); 1292 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK); 1293 1294 file = ERR_PTR(-EINVAL); 1295 if (flags & ~UFFD_SHARED_FCNTL_FLAGS) 1296 goto out; 1297 1298 file = ERR_PTR(-ENOMEM); 1299 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL); 1300 if (!ctx) 1301 goto out; 1302 1303 atomic_set(&ctx->refcount, 1); 1304 ctx->flags = flags; 1305 ctx->state = UFFD_STATE_WAIT_API; 1306 ctx->released = false; 1307 ctx->mm = current->mm; 1308 /* prevent the mm struct to be freed */ 1309 atomic_inc(&ctx->mm->mm_count); 1310 1311 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx, 1312 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS)); 1313 if (IS_ERR(file)) { 1314 mmdrop(ctx->mm); 1315 kmem_cache_free(userfaultfd_ctx_cachep, ctx); 1316 } 1317 out: 1318 return file; 1319 } 1320 1321 SYSCALL_DEFINE1(userfaultfd, int, flags) 1322 { 1323 int fd, error; 1324 struct file *file; 1325 1326 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS); 1327 if (error < 0) 1328 return error; 1329 fd = error; 1330 1331 file = userfaultfd_file_create(flags); 1332 if (IS_ERR(file)) { 1333 error = PTR_ERR(file); 1334 goto err_put_unused_fd; 1335 } 1336 fd_install(fd, file); 1337 1338 return fd; 1339 1340 err_put_unused_fd: 1341 put_unused_fd(fd); 1342 1343 return error; 1344 } 1345 1346 static int __init userfaultfd_init(void) 1347 { 1348 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache", 1349 sizeof(struct userfaultfd_ctx), 1350 0, 1351 SLAB_HWCACHE_ALIGN|SLAB_PANIC, 1352 init_once_userfaultfd_ctx); 1353 return 0; 1354 } 1355 __initcall(userfaultfd_init); 1356