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Linux 6.10-rc2
[thirdparty/kernel/linux.git] / mm / userfaultfd.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * mm/userfaultfd.c
4 *
5 * Copyright (C) 2015 Red Hat, Inc.
6 */
7
8 #include <linux/mm.h>
9 #include <linux/sched/signal.h>
10 #include <linux/pagemap.h>
11 #include <linux/rmap.h>
12 #include <linux/swap.h>
13 #include <linux/swapops.h>
14 #include <linux/userfaultfd_k.h>
15 #include <linux/mmu_notifier.h>
16 #include <linux/hugetlb.h>
17 #include <linux/shmem_fs.h>
18 #include <asm/tlbflush.h>
19 #include <asm/tlb.h>
20 #include "internal.h"
21
22 static __always_inline
23 bool validate_dst_vma(struct vm_area_struct *dst_vma, unsigned long dst_end)
24 {
25 /* Make sure that the dst range is fully within dst_vma. */
26 if (dst_end > dst_vma->vm_end)
27 return false;
28
29 /*
30 * Check the vma is registered in uffd, this is required to
31 * enforce the VM_MAYWRITE check done at uffd registration
32 * time.
33 */
34 if (!dst_vma->vm_userfaultfd_ctx.ctx)
35 return false;
36
37 return true;
38 }
39
40 static __always_inline
41 struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
42 unsigned long addr)
43 {
44 struct vm_area_struct *vma;
45
46 mmap_assert_locked(mm);
47 vma = vma_lookup(mm, addr);
48 if (!vma)
49 vma = ERR_PTR(-ENOENT);
50 else if (!(vma->vm_flags & VM_SHARED) &&
51 unlikely(anon_vma_prepare(vma)))
52 vma = ERR_PTR(-ENOMEM);
53
54 return vma;
55 }
56
57 #ifdef CONFIG_PER_VMA_LOCK
58 /*
59 * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
60 * @mm: mm to search vma in.
61 * @address: address that the vma should contain.
62 *
63 * Should be called without holding mmap_lock.
64 *
65 * Return: A locked vma containing @address, -ENOENT if no vma is found, or
66 * -ENOMEM if anon_vma couldn't be allocated.
67 */
68 static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
69 unsigned long address)
70 {
71 struct vm_area_struct *vma;
72
73 vma = lock_vma_under_rcu(mm, address);
74 if (vma) {
75 /*
76 * We know we're going to need to use anon_vma, so check
77 * that early.
78 */
79 if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
80 vma_end_read(vma);
81 else
82 return vma;
83 }
84
85 mmap_read_lock(mm);
86 vma = find_vma_and_prepare_anon(mm, address);
87 if (!IS_ERR(vma)) {
88 /*
89 * We cannot use vma_start_read() as it may fail due to
90 * false locked (see comment in vma_start_read()). We
91 * can avoid that by directly locking vm_lock under
92 * mmap_lock, which guarantees that nobody can lock the
93 * vma for write (vma_start_write()) under us.
94 */
95 down_read(&vma->vm_lock->lock);
96 }
97
98 mmap_read_unlock(mm);
99 return vma;
100 }
101
102 static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
103 unsigned long dst_start,
104 unsigned long len)
105 {
106 struct vm_area_struct *dst_vma;
107
108 dst_vma = uffd_lock_vma(dst_mm, dst_start);
109 if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
110 return dst_vma;
111
112 vma_end_read(dst_vma);
113 return ERR_PTR(-ENOENT);
114 }
115
116 static void uffd_mfill_unlock(struct vm_area_struct *vma)
117 {
118 vma_end_read(vma);
119 }
120
121 #else
122
123 static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
124 unsigned long dst_start,
125 unsigned long len)
126 {
127 struct vm_area_struct *dst_vma;
128
129 mmap_read_lock(dst_mm);
130 dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
131 if (IS_ERR(dst_vma))
132 goto out_unlock;
133
134 if (validate_dst_vma(dst_vma, dst_start + len))
135 return dst_vma;
136
137 dst_vma = ERR_PTR(-ENOENT);
138 out_unlock:
139 mmap_read_unlock(dst_mm);
140 return dst_vma;
141 }
142
143 static void uffd_mfill_unlock(struct vm_area_struct *vma)
144 {
145 mmap_read_unlock(vma->vm_mm);
146 }
147 #endif
148
149 /* Check if dst_addr is outside of file's size. Must be called with ptl held. */
150 static bool mfill_file_over_size(struct vm_area_struct *dst_vma,
151 unsigned long dst_addr)
152 {
153 struct inode *inode;
154 pgoff_t offset, max_off;
155
156 if (!dst_vma->vm_file)
157 return false;
158
159 inode = dst_vma->vm_file->f_inode;
160 offset = linear_page_index(dst_vma, dst_addr);
161 max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
162 return offset >= max_off;
163 }
164
165 /*
166 * Install PTEs, to map dst_addr (within dst_vma) to page.
167 *
168 * This function handles both MCOPY_ATOMIC_NORMAL and _CONTINUE for both shmem
169 * and anon, and for both shared and private VMAs.
170 */
171 int mfill_atomic_install_pte(pmd_t *dst_pmd,
172 struct vm_area_struct *dst_vma,
173 unsigned long dst_addr, struct page *page,
174 bool newly_allocated, uffd_flags_t flags)
175 {
176 int ret;
177 struct mm_struct *dst_mm = dst_vma->vm_mm;
178 pte_t _dst_pte, *dst_pte;
179 bool writable = dst_vma->vm_flags & VM_WRITE;
180 bool vm_shared = dst_vma->vm_flags & VM_SHARED;
181 spinlock_t *ptl;
182 struct folio *folio = page_folio(page);
183 bool page_in_cache = folio_mapping(folio);
184
185 _dst_pte = mk_pte(page, dst_vma->vm_page_prot);
186 _dst_pte = pte_mkdirty(_dst_pte);
187 if (page_in_cache && !vm_shared)
188 writable = false;
189 if (writable)
190 _dst_pte = pte_mkwrite(_dst_pte, dst_vma);
191 if (flags & MFILL_ATOMIC_WP)
192 _dst_pte = pte_mkuffd_wp(_dst_pte);
193
194 ret = -EAGAIN;
195 dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
196 if (!dst_pte)
197 goto out;
198
199 if (mfill_file_over_size(dst_vma, dst_addr)) {
200 ret = -EFAULT;
201 goto out_unlock;
202 }
203
204 ret = -EEXIST;
205 /*
206 * We allow to overwrite a pte marker: consider when both MISSING|WP
207 * registered, we firstly wr-protect a none pte which has no page cache
208 * page backing it, then access the page.
209 */
210 if (!pte_none_mostly(ptep_get(dst_pte)))
211 goto out_unlock;
212
213 if (page_in_cache) {
214 /* Usually, cache pages are already added to LRU */
215 if (newly_allocated)
216 folio_add_lru(folio);
217 folio_add_file_rmap_pte(folio, page, dst_vma);
218 } else {
219 folio_add_new_anon_rmap(folio, dst_vma, dst_addr);
220 folio_add_lru_vma(folio, dst_vma);
221 }
222
223 /*
224 * Must happen after rmap, as mm_counter() checks mapping (via
225 * PageAnon()), which is set by __page_set_anon_rmap().
226 */
227 inc_mm_counter(dst_mm, mm_counter(folio));
228
229 set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
230
231 /* No need to invalidate - it was non-present before */
232 update_mmu_cache(dst_vma, dst_addr, dst_pte);
233 ret = 0;
234 out_unlock:
235 pte_unmap_unlock(dst_pte, ptl);
236 out:
237 return ret;
238 }
239
240 static int mfill_atomic_pte_copy(pmd_t *dst_pmd,
241 struct vm_area_struct *dst_vma,
242 unsigned long dst_addr,
243 unsigned long src_addr,
244 uffd_flags_t flags,
245 struct folio **foliop)
246 {
247 void *kaddr;
248 int ret;
249 struct folio *folio;
250
251 if (!*foliop) {
252 ret = -ENOMEM;
253 folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma,
254 dst_addr, false);
255 if (!folio)
256 goto out;
257
258 kaddr = kmap_local_folio(folio, 0);
259 /*
260 * The read mmap_lock is held here. Despite the
261 * mmap_lock being read recursive a deadlock is still
262 * possible if a writer has taken a lock. For example:
263 *
264 * process A thread 1 takes read lock on own mmap_lock
265 * process A thread 2 calls mmap, blocks taking write lock
266 * process B thread 1 takes page fault, read lock on own mmap lock
267 * process B thread 2 calls mmap, blocks taking write lock
268 * process A thread 1 blocks taking read lock on process B
269 * process B thread 1 blocks taking read lock on process A
270 *
271 * Disable page faults to prevent potential deadlock
272 * and retry the copy outside the mmap_lock.
273 */
274 pagefault_disable();
275 ret = copy_from_user(kaddr, (const void __user *) src_addr,
276 PAGE_SIZE);
277 pagefault_enable();
278 kunmap_local(kaddr);
279
280 /* fallback to copy_from_user outside mmap_lock */
281 if (unlikely(ret)) {
282 ret = -ENOENT;
283 *foliop = folio;
284 /* don't free the page */
285 goto out;
286 }
287
288 flush_dcache_folio(folio);
289 } else {
290 folio = *foliop;
291 *foliop = NULL;
292 }
293
294 /*
295 * The memory barrier inside __folio_mark_uptodate makes sure that
296 * preceding stores to the page contents become visible before
297 * the set_pte_at() write.
298 */
299 __folio_mark_uptodate(folio);
300
301 ret = -ENOMEM;
302 if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
303 goto out_release;
304
305 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
306 &folio->page, true, flags);
307 if (ret)
308 goto out_release;
309 out:
310 return ret;
311 out_release:
312 folio_put(folio);
313 goto out;
314 }
315
316 static int mfill_atomic_pte_zeroed_folio(pmd_t *dst_pmd,
317 struct vm_area_struct *dst_vma,
318 unsigned long dst_addr)
319 {
320 struct folio *folio;
321 int ret = -ENOMEM;
322
323 folio = vma_alloc_zeroed_movable_folio(dst_vma, dst_addr);
324 if (!folio)
325 return ret;
326
327 if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL))
328 goto out_put;
329
330 /*
331 * The memory barrier inside __folio_mark_uptodate makes sure that
332 * zeroing out the folio become visible before mapping the page
333 * using set_pte_at(). See do_anonymous_page().
334 */
335 __folio_mark_uptodate(folio);
336
337 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
338 &folio->page, true, 0);
339 if (ret)
340 goto out_put;
341
342 return 0;
343 out_put:
344 folio_put(folio);
345 return ret;
346 }
347
348 static int mfill_atomic_pte_zeropage(pmd_t *dst_pmd,
349 struct vm_area_struct *dst_vma,
350 unsigned long dst_addr)
351 {
352 pte_t _dst_pte, *dst_pte;
353 spinlock_t *ptl;
354 int ret;
355
356 if (mm_forbids_zeropage(dst_vma->vm_mm))
357 return mfill_atomic_pte_zeroed_folio(dst_pmd, dst_vma, dst_addr);
358
359 _dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
360 dst_vma->vm_page_prot));
361 ret = -EAGAIN;
362 dst_pte = pte_offset_map_lock(dst_vma->vm_mm, dst_pmd, dst_addr, &ptl);
363 if (!dst_pte)
364 goto out;
365 if (mfill_file_over_size(dst_vma, dst_addr)) {
366 ret = -EFAULT;
367 goto out_unlock;
368 }
369 ret = -EEXIST;
370 if (!pte_none(ptep_get(dst_pte)))
371 goto out_unlock;
372 set_pte_at(dst_vma->vm_mm, dst_addr, dst_pte, _dst_pte);
373 /* No need to invalidate - it was non-present before */
374 update_mmu_cache(dst_vma, dst_addr, dst_pte);
375 ret = 0;
376 out_unlock:
377 pte_unmap_unlock(dst_pte, ptl);
378 out:
379 return ret;
380 }
381
382 /* Handles UFFDIO_CONTINUE for all shmem VMAs (shared or private). */
383 static int mfill_atomic_pte_continue(pmd_t *dst_pmd,
384 struct vm_area_struct *dst_vma,
385 unsigned long dst_addr,
386 uffd_flags_t flags)
387 {
388 struct inode *inode = file_inode(dst_vma->vm_file);
389 pgoff_t pgoff = linear_page_index(dst_vma, dst_addr);
390 struct folio *folio;
391 struct page *page;
392 int ret;
393
394 ret = shmem_get_folio(inode, pgoff, &folio, SGP_NOALLOC);
395 /* Our caller expects us to return -EFAULT if we failed to find folio */
396 if (ret == -ENOENT)
397 ret = -EFAULT;
398 if (ret)
399 goto out;
400 if (!folio) {
401 ret = -EFAULT;
402 goto out;
403 }
404
405 page = folio_file_page(folio, pgoff);
406 if (PageHWPoison(page)) {
407 ret = -EIO;
408 goto out_release;
409 }
410
411 ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr,
412 page, false, flags);
413 if (ret)
414 goto out_release;
415
416 folio_unlock(folio);
417 ret = 0;
418 out:
419 return ret;
420 out_release:
421 folio_unlock(folio);
422 folio_put(folio);
423 goto out;
424 }
425
426 /* Handles UFFDIO_POISON for all non-hugetlb VMAs. */
427 static int mfill_atomic_pte_poison(pmd_t *dst_pmd,
428 struct vm_area_struct *dst_vma,
429 unsigned long dst_addr,
430 uffd_flags_t flags)
431 {
432 int ret;
433 struct mm_struct *dst_mm = dst_vma->vm_mm;
434 pte_t _dst_pte, *dst_pte;
435 spinlock_t *ptl;
436
437 _dst_pte = make_pte_marker(PTE_MARKER_POISONED);
438 ret = -EAGAIN;
439 dst_pte = pte_offset_map_lock(dst_mm, dst_pmd, dst_addr, &ptl);
440 if (!dst_pte)
441 goto out;
442
443 if (mfill_file_over_size(dst_vma, dst_addr)) {
444 ret = -EFAULT;
445 goto out_unlock;
446 }
447
448 ret = -EEXIST;
449 /* Refuse to overwrite any PTE, even a PTE marker (e.g. UFFD WP). */
450 if (!pte_none(ptep_get(dst_pte)))
451 goto out_unlock;
452
453 set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
454
455 /* No need to invalidate - it was non-present before */
456 update_mmu_cache(dst_vma, dst_addr, dst_pte);
457 ret = 0;
458 out_unlock:
459 pte_unmap_unlock(dst_pte, ptl);
460 out:
461 return ret;
462 }
463
464 static pmd_t *mm_alloc_pmd(struct mm_struct *mm, unsigned long address)
465 {
466 pgd_t *pgd;
467 p4d_t *p4d;
468 pud_t *pud;
469
470 pgd = pgd_offset(mm, address);
471 p4d = p4d_alloc(mm, pgd, address);
472 if (!p4d)
473 return NULL;
474 pud = pud_alloc(mm, p4d, address);
475 if (!pud)
476 return NULL;
477 /*
478 * Note that we didn't run this because the pmd was
479 * missing, the *pmd may be already established and in
480 * turn it may also be a trans_huge_pmd.
481 */
482 return pmd_alloc(mm, pud, address);
483 }
484
485 #ifdef CONFIG_HUGETLB_PAGE
486 /*
487 * mfill_atomic processing for HUGETLB vmas. Note that this routine is
488 * called with either vma-lock or mmap_lock held, it will release the lock
489 * before returning.
490 */
491 static __always_inline ssize_t mfill_atomic_hugetlb(
492 struct userfaultfd_ctx *ctx,
493 struct vm_area_struct *dst_vma,
494 unsigned long dst_start,
495 unsigned long src_start,
496 unsigned long len,
497 uffd_flags_t flags)
498 {
499 struct mm_struct *dst_mm = dst_vma->vm_mm;
500 ssize_t err;
501 pte_t *dst_pte;
502 unsigned long src_addr, dst_addr;
503 long copied;
504 struct folio *folio;
505 unsigned long vma_hpagesize;
506 pgoff_t idx;
507 u32 hash;
508 struct address_space *mapping;
509
510 /*
511 * There is no default zero huge page for all huge page sizes as
512 * supported by hugetlb. A PMD_SIZE huge pages may exist as used
513 * by THP. Since we can not reliably insert a zero page, this
514 * feature is not supported.
515 */
516 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_ZEROPAGE)) {
517 up_read(&ctx->map_changing_lock);
518 uffd_mfill_unlock(dst_vma);
519 return -EINVAL;
520 }
521
522 src_addr = src_start;
523 dst_addr = dst_start;
524 copied = 0;
525 folio = NULL;
526 vma_hpagesize = vma_kernel_pagesize(dst_vma);
527
528 /*
529 * Validate alignment based on huge page size
530 */
531 err = -EINVAL;
532 if (dst_start & (vma_hpagesize - 1) || len & (vma_hpagesize - 1))
533 goto out_unlock;
534
535 retry:
536 /*
537 * On routine entry dst_vma is set. If we had to drop mmap_lock and
538 * retry, dst_vma will be set to NULL and we must lookup again.
539 */
540 if (!dst_vma) {
541 dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
542 if (IS_ERR(dst_vma)) {
543 err = PTR_ERR(dst_vma);
544 goto out;
545 }
546
547 err = -ENOENT;
548 if (!is_vm_hugetlb_page(dst_vma))
549 goto out_unlock_vma;
550
551 err = -EINVAL;
552 if (vma_hpagesize != vma_kernel_pagesize(dst_vma))
553 goto out_unlock_vma;
554
555 /*
556 * If memory mappings are changing because of non-cooperative
557 * operation (e.g. mremap) running in parallel, bail out and
558 * request the user to retry later
559 */
560 down_read(&ctx->map_changing_lock);
561 err = -EAGAIN;
562 if (atomic_read(&ctx->mmap_changing))
563 goto out_unlock;
564 }
565
566 while (src_addr < src_start + len) {
567 BUG_ON(dst_addr >= dst_start + len);
568
569 /*
570 * Serialize via vma_lock and hugetlb_fault_mutex.
571 * vma_lock ensures the dst_pte remains valid even
572 * in the case of shared pmds. fault mutex prevents
573 * races with other faulting threads.
574 */
575 idx = linear_page_index(dst_vma, dst_addr);
576 mapping = dst_vma->vm_file->f_mapping;
577 hash = hugetlb_fault_mutex_hash(mapping, idx);
578 mutex_lock(&hugetlb_fault_mutex_table[hash]);
579 hugetlb_vma_lock_read(dst_vma);
580
581 err = -ENOMEM;
582 dst_pte = huge_pte_alloc(dst_mm, dst_vma, dst_addr, vma_hpagesize);
583 if (!dst_pte) {
584 hugetlb_vma_unlock_read(dst_vma);
585 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
586 goto out_unlock;
587 }
588
589 if (!uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE) &&
590 !huge_pte_none_mostly(huge_ptep_get(dst_pte))) {
591 err = -EEXIST;
592 hugetlb_vma_unlock_read(dst_vma);
593 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
594 goto out_unlock;
595 }
596
597 err = hugetlb_mfill_atomic_pte(dst_pte, dst_vma, dst_addr,
598 src_addr, flags, &folio);
599
600 hugetlb_vma_unlock_read(dst_vma);
601 mutex_unlock(&hugetlb_fault_mutex_table[hash]);
602
603 cond_resched();
604
605 if (unlikely(err == -ENOENT)) {
606 up_read(&ctx->map_changing_lock);
607 uffd_mfill_unlock(dst_vma);
608 BUG_ON(!folio);
609
610 err = copy_folio_from_user(folio,
611 (const void __user *)src_addr, true);
612 if (unlikely(err)) {
613 err = -EFAULT;
614 goto out;
615 }
616
617 dst_vma = NULL;
618 goto retry;
619 } else
620 BUG_ON(folio);
621
622 if (!err) {
623 dst_addr += vma_hpagesize;
624 src_addr += vma_hpagesize;
625 copied += vma_hpagesize;
626
627 if (fatal_signal_pending(current))
628 err = -EINTR;
629 }
630 if (err)
631 break;
632 }
633
634 out_unlock:
635 up_read(&ctx->map_changing_lock);
636 out_unlock_vma:
637 uffd_mfill_unlock(dst_vma);
638 out:
639 if (folio)
640 folio_put(folio);
641 BUG_ON(copied < 0);
642 BUG_ON(err > 0);
643 BUG_ON(!copied && !err);
644 return copied ? copied : err;
645 }
646 #else /* !CONFIG_HUGETLB_PAGE */
647 /* fail at build time if gcc attempts to use this */
648 extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
649 struct vm_area_struct *dst_vma,
650 unsigned long dst_start,
651 unsigned long src_start,
652 unsigned long len,
653 uffd_flags_t flags);
654 #endif /* CONFIG_HUGETLB_PAGE */
655
656 static __always_inline ssize_t mfill_atomic_pte(pmd_t *dst_pmd,
657 struct vm_area_struct *dst_vma,
658 unsigned long dst_addr,
659 unsigned long src_addr,
660 uffd_flags_t flags,
661 struct folio **foliop)
662 {
663 ssize_t err;
664
665 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE)) {
666 return mfill_atomic_pte_continue(dst_pmd, dst_vma,
667 dst_addr, flags);
668 } else if (uffd_flags_mode_is(flags, MFILL_ATOMIC_POISON)) {
669 return mfill_atomic_pte_poison(dst_pmd, dst_vma,
670 dst_addr, flags);
671 }
672
673 /*
674 * The normal page fault path for a shmem will invoke the
675 * fault, fill the hole in the file and COW it right away. The
676 * result generates plain anonymous memory. So when we are
677 * asked to fill an hole in a MAP_PRIVATE shmem mapping, we'll
678 * generate anonymous memory directly without actually filling
679 * the hole. For the MAP_PRIVATE case the robustness check
680 * only happens in the pagetable (to verify it's still none)
681 * and not in the radix tree.
682 */
683 if (!(dst_vma->vm_flags & VM_SHARED)) {
684 if (uffd_flags_mode_is(flags, MFILL_ATOMIC_COPY))
685 err = mfill_atomic_pte_copy(dst_pmd, dst_vma,
686 dst_addr, src_addr,
687 flags, foliop);
688 else
689 err = mfill_atomic_pte_zeropage(dst_pmd,
690 dst_vma, dst_addr);
691 } else {
692 err = shmem_mfill_atomic_pte(dst_pmd, dst_vma,
693 dst_addr, src_addr,
694 flags, foliop);
695 }
696
697 return err;
698 }
699
700 static __always_inline ssize_t mfill_atomic(struct userfaultfd_ctx *ctx,
701 unsigned long dst_start,
702 unsigned long src_start,
703 unsigned long len,
704 uffd_flags_t flags)
705 {
706 struct mm_struct *dst_mm = ctx->mm;
707 struct vm_area_struct *dst_vma;
708 ssize_t err;
709 pmd_t *dst_pmd;
710 unsigned long src_addr, dst_addr;
711 long copied;
712 struct folio *folio;
713
714 /*
715 * Sanitize the command parameters:
716 */
717 BUG_ON(dst_start & ~PAGE_MASK);
718 BUG_ON(len & ~PAGE_MASK);
719
720 /* Does the address range wrap, or is the span zero-sized? */
721 BUG_ON(src_start + len <= src_start);
722 BUG_ON(dst_start + len <= dst_start);
723
724 src_addr = src_start;
725 dst_addr = dst_start;
726 copied = 0;
727 folio = NULL;
728 retry:
729 /*
730 * Make sure the vma is not shared, that the dst range is
731 * both valid and fully within a single existing vma.
732 */
733 dst_vma = uffd_mfill_lock(dst_mm, dst_start, len);
734 if (IS_ERR(dst_vma)) {
735 err = PTR_ERR(dst_vma);
736 goto out;
737 }
738
739 /*
740 * If memory mappings are changing because of non-cooperative
741 * operation (e.g. mremap) running in parallel, bail out and
742 * request the user to retry later
743 */
744 down_read(&ctx->map_changing_lock);
745 err = -EAGAIN;
746 if (atomic_read(&ctx->mmap_changing))
747 goto out_unlock;
748
749 err = -EINVAL;
750 /*
751 * shmem_zero_setup is invoked in mmap for MAP_ANONYMOUS|MAP_SHARED but
752 * it will overwrite vm_ops, so vma_is_anonymous must return false.
753 */
754 if (WARN_ON_ONCE(vma_is_anonymous(dst_vma) &&
755 dst_vma->vm_flags & VM_SHARED))
756 goto out_unlock;
757
758 /*
759 * validate 'mode' now that we know the dst_vma: don't allow
760 * a wrprotect copy if the userfaultfd didn't register as WP.
761 */
762 if ((flags & MFILL_ATOMIC_WP) && !(dst_vma->vm_flags & VM_UFFD_WP))
763 goto out_unlock;
764
765 /*
766 * If this is a HUGETLB vma, pass off to appropriate routine
767 */
768 if (is_vm_hugetlb_page(dst_vma))
769 return mfill_atomic_hugetlb(ctx, dst_vma, dst_start,
770 src_start, len, flags);
771
772 if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
773 goto out_unlock;
774 if (!vma_is_shmem(dst_vma) &&
775 uffd_flags_mode_is(flags, MFILL_ATOMIC_CONTINUE))
776 goto out_unlock;
777
778 while (src_addr < src_start + len) {
779 pmd_t dst_pmdval;
780
781 BUG_ON(dst_addr >= dst_start + len);
782
783 dst_pmd = mm_alloc_pmd(dst_mm, dst_addr);
784 if (unlikely(!dst_pmd)) {
785 err = -ENOMEM;
786 break;
787 }
788
789 dst_pmdval = pmdp_get_lockless(dst_pmd);
790 /*
791 * If the dst_pmd is mapped as THP don't
792 * override it and just be strict.
793 */
794 if (unlikely(pmd_trans_huge(dst_pmdval))) {
795 err = -EEXIST;
796 break;
797 }
798 if (unlikely(pmd_none(dst_pmdval)) &&
799 unlikely(__pte_alloc(dst_mm, dst_pmd))) {
800 err = -ENOMEM;
801 break;
802 }
803 /* If an huge pmd materialized from under us fail */
804 if (unlikely(pmd_trans_huge(*dst_pmd))) {
805 err = -EFAULT;
806 break;
807 }
808
809 BUG_ON(pmd_none(*dst_pmd));
810 BUG_ON(pmd_trans_huge(*dst_pmd));
811
812 err = mfill_atomic_pte(dst_pmd, dst_vma, dst_addr,
813 src_addr, flags, &folio);
814 cond_resched();
815
816 if (unlikely(err == -ENOENT)) {
817 void *kaddr;
818
819 up_read(&ctx->map_changing_lock);
820 uffd_mfill_unlock(dst_vma);
821 BUG_ON(!folio);
822
823 kaddr = kmap_local_folio(folio, 0);
824 err = copy_from_user(kaddr,
825 (const void __user *) src_addr,
826 PAGE_SIZE);
827 kunmap_local(kaddr);
828 if (unlikely(err)) {
829 err = -EFAULT;
830 goto out;
831 }
832 flush_dcache_folio(folio);
833 goto retry;
834 } else
835 BUG_ON(folio);
836
837 if (!err) {
838 dst_addr += PAGE_SIZE;
839 src_addr += PAGE_SIZE;
840 copied += PAGE_SIZE;
841
842 if (fatal_signal_pending(current))
843 err = -EINTR;
844 }
845 if (err)
846 break;
847 }
848
849 out_unlock:
850 up_read(&ctx->map_changing_lock);
851 uffd_mfill_unlock(dst_vma);
852 out:
853 if (folio)
854 folio_put(folio);
855 BUG_ON(copied < 0);
856 BUG_ON(err > 0);
857 BUG_ON(!copied && !err);
858 return copied ? copied : err;
859 }
860
861 ssize_t mfill_atomic_copy(struct userfaultfd_ctx *ctx, unsigned long dst_start,
862 unsigned long src_start, unsigned long len,
863 uffd_flags_t flags)
864 {
865 return mfill_atomic(ctx, dst_start, src_start, len,
866 uffd_flags_set_mode(flags, MFILL_ATOMIC_COPY));
867 }
868
869 ssize_t mfill_atomic_zeropage(struct userfaultfd_ctx *ctx,
870 unsigned long start,
871 unsigned long len)
872 {
873 return mfill_atomic(ctx, start, 0, len,
874 uffd_flags_set_mode(0, MFILL_ATOMIC_ZEROPAGE));
875 }
876
877 ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long start,
878 unsigned long len, uffd_flags_t flags)
879 {
880
881 /*
882 * A caller might reasonably assume that UFFDIO_CONTINUE contains an
883 * smp_wmb() to ensure that any writes to the about-to-be-mapped page by
884 * the thread doing the UFFDIO_CONTINUE are guaranteed to be visible to
885 * subsequent loads from the page through the newly mapped address range.
886 */
887 smp_wmb();
888
889 return mfill_atomic(ctx, start, 0, len,
890 uffd_flags_set_mode(flags, MFILL_ATOMIC_CONTINUE));
891 }
892
893 ssize_t mfill_atomic_poison(struct userfaultfd_ctx *ctx, unsigned long start,
894 unsigned long len, uffd_flags_t flags)
895 {
896 return mfill_atomic(ctx, start, 0, len,
897 uffd_flags_set_mode(flags, MFILL_ATOMIC_POISON));
898 }
899
900 long uffd_wp_range(struct vm_area_struct *dst_vma,
901 unsigned long start, unsigned long len, bool enable_wp)
902 {
903 unsigned int mm_cp_flags;
904 struct mmu_gather tlb;
905 long ret;
906
907 VM_WARN_ONCE(start < dst_vma->vm_start || start + len > dst_vma->vm_end,
908 "The address range exceeds VMA boundary.\n");
909 if (enable_wp)
910 mm_cp_flags = MM_CP_UFFD_WP;
911 else
912 mm_cp_flags = MM_CP_UFFD_WP_RESOLVE;
913
914 /*
915 * vma->vm_page_prot already reflects that uffd-wp is enabled for this
916 * VMA (see userfaultfd_set_vm_flags()) and that all PTEs are supposed
917 * to be write-protected as default whenever protection changes.
918 * Try upgrading write permissions manually.
919 */
920 if (!enable_wp && vma_wants_manual_pte_write_upgrade(dst_vma))
921 mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
922 tlb_gather_mmu(&tlb, dst_vma->vm_mm);
923 ret = change_protection(&tlb, dst_vma, start, start + len, mm_cp_flags);
924 tlb_finish_mmu(&tlb);
925
926 return ret;
927 }
928
929 int mwriteprotect_range(struct userfaultfd_ctx *ctx, unsigned long start,
930 unsigned long len, bool enable_wp)
931 {
932 struct mm_struct *dst_mm = ctx->mm;
933 unsigned long end = start + len;
934 unsigned long _start, _end;
935 struct vm_area_struct *dst_vma;
936 unsigned long page_mask;
937 long err;
938 VMA_ITERATOR(vmi, dst_mm, start);
939
940 /*
941 * Sanitize the command parameters:
942 */
943 BUG_ON(start & ~PAGE_MASK);
944 BUG_ON(len & ~PAGE_MASK);
945
946 /* Does the address range wrap, or is the span zero-sized? */
947 BUG_ON(start + len <= start);
948
949 mmap_read_lock(dst_mm);
950
951 /*
952 * If memory mappings are changing because of non-cooperative
953 * operation (e.g. mremap) running in parallel, bail out and
954 * request the user to retry later
955 */
956 down_read(&ctx->map_changing_lock);
957 err = -EAGAIN;
958 if (atomic_read(&ctx->mmap_changing))
959 goto out_unlock;
960
961 err = -ENOENT;
962 for_each_vma_range(vmi, dst_vma, end) {
963
964 if (!userfaultfd_wp(dst_vma)) {
965 err = -ENOENT;
966 break;
967 }
968
969 if (is_vm_hugetlb_page(dst_vma)) {
970 err = -EINVAL;
971 page_mask = vma_kernel_pagesize(dst_vma) - 1;
972 if ((start & page_mask) || (len & page_mask))
973 break;
974 }
975
976 _start = max(dst_vma->vm_start, start);
977 _end = min(dst_vma->vm_end, end);
978
979 err = uffd_wp_range(dst_vma, _start, _end - _start, enable_wp);
980
981 /* Return 0 on success, <0 on failures */
982 if (err < 0)
983 break;
984 err = 0;
985 }
986 out_unlock:
987 up_read(&ctx->map_changing_lock);
988 mmap_read_unlock(dst_mm);
989 return err;
990 }
991
992
993 void double_pt_lock(spinlock_t *ptl1,
994 spinlock_t *ptl2)
995 __acquires(ptl1)
996 __acquires(ptl2)
997 {
998 spinlock_t *ptl_tmp;
999
1000 if (ptl1 > ptl2) {
1001 /* exchange ptl1 and ptl2 */
1002 ptl_tmp = ptl1;
1003 ptl1 = ptl2;
1004 ptl2 = ptl_tmp;
1005 }
1006 /* lock in virtual address order to avoid lock inversion */
1007 spin_lock(ptl1);
1008 if (ptl1 != ptl2)
1009 spin_lock_nested(ptl2, SINGLE_DEPTH_NESTING);
1010 else
1011 __acquire(ptl2);
1012 }
1013
1014 void double_pt_unlock(spinlock_t *ptl1,
1015 spinlock_t *ptl2)
1016 __releases(ptl1)
1017 __releases(ptl2)
1018 {
1019 spin_unlock(ptl1);
1020 if (ptl1 != ptl2)
1021 spin_unlock(ptl2);
1022 else
1023 __release(ptl2);
1024 }
1025
1026
1027 static int move_present_pte(struct mm_struct *mm,
1028 struct vm_area_struct *dst_vma,
1029 struct vm_area_struct *src_vma,
1030 unsigned long dst_addr, unsigned long src_addr,
1031 pte_t *dst_pte, pte_t *src_pte,
1032 pte_t orig_dst_pte, pte_t orig_src_pte,
1033 spinlock_t *dst_ptl, spinlock_t *src_ptl,
1034 struct folio *src_folio)
1035 {
1036 int err = 0;
1037
1038 double_pt_lock(dst_ptl, src_ptl);
1039
1040 if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
1041 !pte_same(ptep_get(dst_pte), orig_dst_pte)) {
1042 err = -EAGAIN;
1043 goto out;
1044 }
1045 if (folio_test_large(src_folio) ||
1046 folio_maybe_dma_pinned(src_folio) ||
1047 !PageAnonExclusive(&src_folio->page)) {
1048 err = -EBUSY;
1049 goto out;
1050 }
1051
1052 orig_src_pte = ptep_clear_flush(src_vma, src_addr, src_pte);
1053 /* Folio got pinned from under us. Put it back and fail the move. */
1054 if (folio_maybe_dma_pinned(src_folio)) {
1055 set_pte_at(mm, src_addr, src_pte, orig_src_pte);
1056 err = -EBUSY;
1057 goto out;
1058 }
1059
1060 folio_move_anon_rmap(src_folio, dst_vma);
1061 src_folio->index = linear_page_index(dst_vma, dst_addr);
1062
1063 orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
1064 /* Follow mremap() behavior and treat the entry dirty after the move */
1065 orig_dst_pte = pte_mkwrite(pte_mkdirty(orig_dst_pte), dst_vma);
1066
1067 set_pte_at(mm, dst_addr, dst_pte, orig_dst_pte);
1068 out:
1069 double_pt_unlock(dst_ptl, src_ptl);
1070 return err;
1071 }
1072
1073 static int move_swap_pte(struct mm_struct *mm,
1074 unsigned long dst_addr, unsigned long src_addr,
1075 pte_t *dst_pte, pte_t *src_pte,
1076 pte_t orig_dst_pte, pte_t orig_src_pte,
1077 spinlock_t *dst_ptl, spinlock_t *src_ptl)
1078 {
1079 if (!pte_swp_exclusive(orig_src_pte))
1080 return -EBUSY;
1081
1082 double_pt_lock(dst_ptl, src_ptl);
1083
1084 if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
1085 !pte_same(ptep_get(dst_pte), orig_dst_pte)) {
1086 double_pt_unlock(dst_ptl, src_ptl);
1087 return -EAGAIN;
1088 }
1089
1090 orig_src_pte = ptep_get_and_clear(mm, src_addr, src_pte);
1091 set_pte_at(mm, dst_addr, dst_pte, orig_src_pte);
1092 double_pt_unlock(dst_ptl, src_ptl);
1093
1094 return 0;
1095 }
1096
1097 static int move_zeropage_pte(struct mm_struct *mm,
1098 struct vm_area_struct *dst_vma,
1099 struct vm_area_struct *src_vma,
1100 unsigned long dst_addr, unsigned long src_addr,
1101 pte_t *dst_pte, pte_t *src_pte,
1102 pte_t orig_dst_pte, pte_t orig_src_pte,
1103 spinlock_t *dst_ptl, spinlock_t *src_ptl)
1104 {
1105 pte_t zero_pte;
1106
1107 double_pt_lock(dst_ptl, src_ptl);
1108 if (!pte_same(ptep_get(src_pte), orig_src_pte) ||
1109 !pte_same(ptep_get(dst_pte), orig_dst_pte)) {
1110 double_pt_unlock(dst_ptl, src_ptl);
1111 return -EAGAIN;
1112 }
1113
1114 zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
1115 dst_vma->vm_page_prot));
1116 ptep_clear_flush(src_vma, src_addr, src_pte);
1117 set_pte_at(mm, dst_addr, dst_pte, zero_pte);
1118 double_pt_unlock(dst_ptl, src_ptl);
1119
1120 return 0;
1121 }
1122
1123
1124 /*
1125 * The mmap_lock for reading is held by the caller. Just move the page
1126 * from src_pmd to dst_pmd if possible, and return true if succeeded
1127 * in moving the page.
1128 */
1129 static int move_pages_pte(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd,
1130 struct vm_area_struct *dst_vma,
1131 struct vm_area_struct *src_vma,
1132 unsigned long dst_addr, unsigned long src_addr,
1133 __u64 mode)
1134 {
1135 swp_entry_t entry;
1136 pte_t orig_src_pte, orig_dst_pte;
1137 pte_t src_folio_pte;
1138 spinlock_t *src_ptl, *dst_ptl;
1139 pte_t *src_pte = NULL;
1140 pte_t *dst_pte = NULL;
1141
1142 struct folio *src_folio = NULL;
1143 struct anon_vma *src_anon_vma = NULL;
1144 struct mmu_notifier_range range;
1145 int err = 0;
1146
1147 flush_cache_range(src_vma, src_addr, src_addr + PAGE_SIZE);
1148 mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
1149 src_addr, src_addr + PAGE_SIZE);
1150 mmu_notifier_invalidate_range_start(&range);
1151 retry:
1152 dst_pte = pte_offset_map_nolock(mm, dst_pmd, dst_addr, &dst_ptl);
1153
1154 /* Retry if a huge pmd materialized from under us */
1155 if (unlikely(!dst_pte)) {
1156 err = -EAGAIN;
1157 goto out;
1158 }
1159
1160 src_pte = pte_offset_map_nolock(mm, src_pmd, src_addr, &src_ptl);
1161
1162 /*
1163 * We held the mmap_lock for reading so MADV_DONTNEED
1164 * can zap transparent huge pages under us, or the
1165 * transparent huge page fault can establish new
1166 * transparent huge pages under us.
1167 */
1168 if (unlikely(!src_pte)) {
1169 err = -EAGAIN;
1170 goto out;
1171 }
1172
1173 /* Sanity checks before the operation */
1174 if (WARN_ON_ONCE(pmd_none(*dst_pmd)) || WARN_ON_ONCE(pmd_none(*src_pmd)) ||
1175 WARN_ON_ONCE(pmd_trans_huge(*dst_pmd)) || WARN_ON_ONCE(pmd_trans_huge(*src_pmd))) {
1176 err = -EINVAL;
1177 goto out;
1178 }
1179
1180 spin_lock(dst_ptl);
1181 orig_dst_pte = ptep_get(dst_pte);
1182 spin_unlock(dst_ptl);
1183 if (!pte_none(orig_dst_pte)) {
1184 err = -EEXIST;
1185 goto out;
1186 }
1187
1188 spin_lock(src_ptl);
1189 orig_src_pte = ptep_get(src_pte);
1190 spin_unlock(src_ptl);
1191 if (pte_none(orig_src_pte)) {
1192 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES))
1193 err = -ENOENT;
1194 else /* nothing to do to move a hole */
1195 err = 0;
1196 goto out;
1197 }
1198
1199 /* If PTE changed after we locked the folio them start over */
1200 if (src_folio && unlikely(!pte_same(src_folio_pte, orig_src_pte))) {
1201 err = -EAGAIN;
1202 goto out;
1203 }
1204
1205 if (pte_present(orig_src_pte)) {
1206 if (is_zero_pfn(pte_pfn(orig_src_pte))) {
1207 err = move_zeropage_pte(mm, dst_vma, src_vma,
1208 dst_addr, src_addr, dst_pte, src_pte,
1209 orig_dst_pte, orig_src_pte,
1210 dst_ptl, src_ptl);
1211 goto out;
1212 }
1213
1214 /*
1215 * Pin and lock both source folio and anon_vma. Since we are in
1216 * RCU read section, we can't block, so on contention have to
1217 * unmap the ptes, obtain the lock and retry.
1218 */
1219 if (!src_folio) {
1220 struct folio *folio;
1221
1222 /*
1223 * Pin the page while holding the lock to be sure the
1224 * page isn't freed under us
1225 */
1226 spin_lock(src_ptl);
1227 if (!pte_same(orig_src_pte, ptep_get(src_pte))) {
1228 spin_unlock(src_ptl);
1229 err = -EAGAIN;
1230 goto out;
1231 }
1232
1233 folio = vm_normal_folio(src_vma, src_addr, orig_src_pte);
1234 if (!folio || !PageAnonExclusive(&folio->page)) {
1235 spin_unlock(src_ptl);
1236 err = -EBUSY;
1237 goto out;
1238 }
1239
1240 folio_get(folio);
1241 src_folio = folio;
1242 src_folio_pte = orig_src_pte;
1243 spin_unlock(src_ptl);
1244
1245 if (!folio_trylock(src_folio)) {
1246 pte_unmap(&orig_src_pte);
1247 pte_unmap(&orig_dst_pte);
1248 src_pte = dst_pte = NULL;
1249 /* now we can block and wait */
1250 folio_lock(src_folio);
1251 goto retry;
1252 }
1253
1254 if (WARN_ON_ONCE(!folio_test_anon(src_folio))) {
1255 err = -EBUSY;
1256 goto out;
1257 }
1258 }
1259
1260 /* at this point we have src_folio locked */
1261 if (folio_test_large(src_folio)) {
1262 /* split_folio() can block */
1263 pte_unmap(&orig_src_pte);
1264 pte_unmap(&orig_dst_pte);
1265 src_pte = dst_pte = NULL;
1266 err = split_folio(src_folio);
1267 if (err)
1268 goto out;
1269 /* have to reacquire the folio after it got split */
1270 folio_unlock(src_folio);
1271 folio_put(src_folio);
1272 src_folio = NULL;
1273 goto retry;
1274 }
1275
1276 if (!src_anon_vma) {
1277 /*
1278 * folio_referenced walks the anon_vma chain
1279 * without the folio lock. Serialize against it with
1280 * the anon_vma lock, the folio lock is not enough.
1281 */
1282 src_anon_vma = folio_get_anon_vma(src_folio);
1283 if (!src_anon_vma) {
1284 /* page was unmapped from under us */
1285 err = -EAGAIN;
1286 goto out;
1287 }
1288 if (!anon_vma_trylock_write(src_anon_vma)) {
1289 pte_unmap(&orig_src_pte);
1290 pte_unmap(&orig_dst_pte);
1291 src_pte = dst_pte = NULL;
1292 /* now we can block and wait */
1293 anon_vma_lock_write(src_anon_vma);
1294 goto retry;
1295 }
1296 }
1297
1298 err = move_present_pte(mm, dst_vma, src_vma,
1299 dst_addr, src_addr, dst_pte, src_pte,
1300 orig_dst_pte, orig_src_pte,
1301 dst_ptl, src_ptl, src_folio);
1302 } else {
1303 entry = pte_to_swp_entry(orig_src_pte);
1304 if (non_swap_entry(entry)) {
1305 if (is_migration_entry(entry)) {
1306 pte_unmap(&orig_src_pte);
1307 pte_unmap(&orig_dst_pte);
1308 src_pte = dst_pte = NULL;
1309 migration_entry_wait(mm, src_pmd, src_addr);
1310 err = -EAGAIN;
1311 } else
1312 err = -EFAULT;
1313 goto out;
1314 }
1315
1316 err = move_swap_pte(mm, dst_addr, src_addr,
1317 dst_pte, src_pte,
1318 orig_dst_pte, orig_src_pte,
1319 dst_ptl, src_ptl);
1320 }
1321
1322 out:
1323 if (src_anon_vma) {
1324 anon_vma_unlock_write(src_anon_vma);
1325 put_anon_vma(src_anon_vma);
1326 }
1327 if (src_folio) {
1328 folio_unlock(src_folio);
1329 folio_put(src_folio);
1330 }
1331 if (dst_pte)
1332 pte_unmap(dst_pte);
1333 if (src_pte)
1334 pte_unmap(src_pte);
1335 mmu_notifier_invalidate_range_end(&range);
1336
1337 return err;
1338 }
1339
1340 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
1341 static inline bool move_splits_huge_pmd(unsigned long dst_addr,
1342 unsigned long src_addr,
1343 unsigned long src_end)
1344 {
1345 return (src_addr & ~HPAGE_PMD_MASK) || (dst_addr & ~HPAGE_PMD_MASK) ||
1346 src_end - src_addr < HPAGE_PMD_SIZE;
1347 }
1348 #else
1349 static inline bool move_splits_huge_pmd(unsigned long dst_addr,
1350 unsigned long src_addr,
1351 unsigned long src_end)
1352 {
1353 /* This is unreachable anyway, just to avoid warnings when HPAGE_PMD_SIZE==0 */
1354 return false;
1355 }
1356 #endif
1357
1358 static inline bool vma_move_compatible(struct vm_area_struct *vma)
1359 {
1360 return !(vma->vm_flags & (VM_PFNMAP | VM_IO | VM_HUGETLB |
1361 VM_MIXEDMAP | VM_SHADOW_STACK));
1362 }
1363
1364 static int validate_move_areas(struct userfaultfd_ctx *ctx,
1365 struct vm_area_struct *src_vma,
1366 struct vm_area_struct *dst_vma)
1367 {
1368 /* Only allow moving if both have the same access and protection */
1369 if ((src_vma->vm_flags & VM_ACCESS_FLAGS) != (dst_vma->vm_flags & VM_ACCESS_FLAGS) ||
1370 pgprot_val(src_vma->vm_page_prot) != pgprot_val(dst_vma->vm_page_prot))
1371 return -EINVAL;
1372
1373 /* Only allow moving if both are mlocked or both aren't */
1374 if ((src_vma->vm_flags & VM_LOCKED) != (dst_vma->vm_flags & VM_LOCKED))
1375 return -EINVAL;
1376
1377 /*
1378 * For now, we keep it simple and only move between writable VMAs.
1379 * Access flags are equal, therefore cheching only the source is enough.
1380 */
1381 if (!(src_vma->vm_flags & VM_WRITE))
1382 return -EINVAL;
1383
1384 /* Check if vma flags indicate content which can be moved */
1385 if (!vma_move_compatible(src_vma) || !vma_move_compatible(dst_vma))
1386 return -EINVAL;
1387
1388 /* Ensure dst_vma is registered in uffd we are operating on */
1389 if (!dst_vma->vm_userfaultfd_ctx.ctx ||
1390 dst_vma->vm_userfaultfd_ctx.ctx != ctx)
1391 return -EINVAL;
1392
1393 /* Only allow moving across anonymous vmas */
1394 if (!vma_is_anonymous(src_vma) || !vma_is_anonymous(dst_vma))
1395 return -EINVAL;
1396
1397 return 0;
1398 }
1399
1400 static __always_inline
1401 int find_vmas_mm_locked(struct mm_struct *mm,
1402 unsigned long dst_start,
1403 unsigned long src_start,
1404 struct vm_area_struct **dst_vmap,
1405 struct vm_area_struct **src_vmap)
1406 {
1407 struct vm_area_struct *vma;
1408
1409 mmap_assert_locked(mm);
1410 vma = find_vma_and_prepare_anon(mm, dst_start);
1411 if (IS_ERR(vma))
1412 return PTR_ERR(vma);
1413
1414 *dst_vmap = vma;
1415 /* Skip finding src_vma if src_start is in dst_vma */
1416 if (src_start >= vma->vm_start && src_start < vma->vm_end)
1417 goto out_success;
1418
1419 vma = vma_lookup(mm, src_start);
1420 if (!vma)
1421 return -ENOENT;
1422 out_success:
1423 *src_vmap = vma;
1424 return 0;
1425 }
1426
1427 #ifdef CONFIG_PER_VMA_LOCK
1428 static int uffd_move_lock(struct mm_struct *mm,
1429 unsigned long dst_start,
1430 unsigned long src_start,
1431 struct vm_area_struct **dst_vmap,
1432 struct vm_area_struct **src_vmap)
1433 {
1434 struct vm_area_struct *vma;
1435 int err;
1436
1437 vma = uffd_lock_vma(mm, dst_start);
1438 if (IS_ERR(vma))
1439 return PTR_ERR(vma);
1440
1441 *dst_vmap = vma;
1442 /*
1443 * Skip finding src_vma if src_start is in dst_vma. This also ensures
1444 * that we don't lock the same vma twice.
1445 */
1446 if (src_start >= vma->vm_start && src_start < vma->vm_end) {
1447 *src_vmap = vma;
1448 return 0;
1449 }
1450
1451 /*
1452 * Using uffd_lock_vma() to get src_vma can lead to following deadlock:
1453 *
1454 * Thread1 Thread2
1455 * ------- -------
1456 * vma_start_read(dst_vma)
1457 * mmap_write_lock(mm)
1458 * vma_start_write(src_vma)
1459 * vma_start_read(src_vma)
1460 * mmap_read_lock(mm)
1461 * vma_start_write(dst_vma)
1462 */
1463 *src_vmap = lock_vma_under_rcu(mm, src_start);
1464 if (likely(*src_vmap))
1465 return 0;
1466
1467 /* Undo any locking and retry in mmap_lock critical section */
1468 vma_end_read(*dst_vmap);
1469
1470 mmap_read_lock(mm);
1471 err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
1472 if (!err) {
1473 /*
1474 * See comment in uffd_lock_vma() as to why not using
1475 * vma_start_read() here.
1476 */
1477 down_read(&(*dst_vmap)->vm_lock->lock);
1478 if (*dst_vmap != *src_vmap)
1479 down_read_nested(&(*src_vmap)->vm_lock->lock,
1480 SINGLE_DEPTH_NESTING);
1481 }
1482 mmap_read_unlock(mm);
1483 return err;
1484 }
1485
1486 static void uffd_move_unlock(struct vm_area_struct *dst_vma,
1487 struct vm_area_struct *src_vma)
1488 {
1489 vma_end_read(src_vma);
1490 if (src_vma != dst_vma)
1491 vma_end_read(dst_vma);
1492 }
1493
1494 #else
1495
1496 static int uffd_move_lock(struct mm_struct *mm,
1497 unsigned long dst_start,
1498 unsigned long src_start,
1499 struct vm_area_struct **dst_vmap,
1500 struct vm_area_struct **src_vmap)
1501 {
1502 int err;
1503
1504 mmap_read_lock(mm);
1505 err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
1506 if (err)
1507 mmap_read_unlock(mm);
1508 return err;
1509 }
1510
1511 static void uffd_move_unlock(struct vm_area_struct *dst_vma,
1512 struct vm_area_struct *src_vma)
1513 {
1514 mmap_assert_locked(src_vma->vm_mm);
1515 mmap_read_unlock(dst_vma->vm_mm);
1516 }
1517 #endif
1518
1519 /**
1520 * move_pages - move arbitrary anonymous pages of an existing vma
1521 * @ctx: pointer to the userfaultfd context
1522 * @dst_start: start of the destination virtual memory range
1523 * @src_start: start of the source virtual memory range
1524 * @len: length of the virtual memory range
1525 * @mode: flags from uffdio_move.mode
1526 *
1527 * It will either use the mmap_lock in read mode or per-vma locks
1528 *
1529 * move_pages() remaps arbitrary anonymous pages atomically in zero
1530 * copy. It only works on non shared anonymous pages because those can
1531 * be relocated without generating non linear anon_vmas in the rmap
1532 * code.
1533 *
1534 * It provides a zero copy mechanism to handle userspace page faults.
1535 * The source vma pages should have mapcount == 1, which can be
1536 * enforced by using madvise(MADV_DONTFORK) on src vma.
1537 *
1538 * The thread receiving the page during the userland page fault
1539 * will receive the faulting page in the source vma through the network,
1540 * storage or any other I/O device (MADV_DONTFORK in the source vma
1541 * avoids move_pages() to fail with -EBUSY if the process forks before
1542 * move_pages() is called), then it will call move_pages() to map the
1543 * page in the faulting address in the destination vma.
1544 *
1545 * This userfaultfd command works purely via pagetables, so it's the
1546 * most efficient way to move physical non shared anonymous pages
1547 * across different virtual addresses. Unlike mremap()/mmap()/munmap()
1548 * it does not create any new vmas. The mapping in the destination
1549 * address is atomic.
1550 *
1551 * It only works if the vma protection bits are identical from the
1552 * source and destination vma.
1553 *
1554 * It can remap non shared anonymous pages within the same vma too.
1555 *
1556 * If the source virtual memory range has any unmapped holes, or if
1557 * the destination virtual memory range is not a whole unmapped hole,
1558 * move_pages() will fail respectively with -ENOENT or -EEXIST. This
1559 * provides a very strict behavior to avoid any chance of memory
1560 * corruption going unnoticed if there are userland race conditions.
1561 * Only one thread should resolve the userland page fault at any given
1562 * time for any given faulting address. This means that if two threads
1563 * try to both call move_pages() on the same destination address at the
1564 * same time, the second thread will get an explicit error from this
1565 * command.
1566 *
1567 * The command retval will return "len" is successful. The command
1568 * however can be interrupted by fatal signals or errors. If
1569 * interrupted it will return the number of bytes successfully
1570 * remapped before the interruption if any, or the negative error if
1571 * none. It will never return zero. Either it will return an error or
1572 * an amount of bytes successfully moved. If the retval reports a
1573 * "short" remap, the move_pages() command should be repeated by
1574 * userland with src+retval, dst+reval, len-retval if it wants to know
1575 * about the error that interrupted it.
1576 *
1577 * The UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES flag can be specified to
1578 * prevent -ENOENT errors to materialize if there are holes in the
1579 * source virtual range that is being remapped. The holes will be
1580 * accounted as successfully remapped in the retval of the
1581 * command. This is mostly useful to remap hugepage naturally aligned
1582 * virtual regions without knowing if there are transparent hugepage
1583 * in the regions or not, but preventing the risk of having to split
1584 * the hugepmd during the remap.
1585 *
1586 * If there's any rmap walk that is taking the anon_vma locks without
1587 * first obtaining the folio lock (the only current instance is
1588 * folio_referenced), they will have to verify if the folio->mapping
1589 * has changed after taking the anon_vma lock. If it changed they
1590 * should release the lock and retry obtaining a new anon_vma, because
1591 * it means the anon_vma was changed by move_pages() before the lock
1592 * could be obtained. This is the only additional complexity added to
1593 * the rmap code to provide this anonymous page remapping functionality.
1594 */
1595 ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start,
1596 unsigned long src_start, unsigned long len, __u64 mode)
1597 {
1598 struct mm_struct *mm = ctx->mm;
1599 struct vm_area_struct *src_vma, *dst_vma;
1600 unsigned long src_addr, dst_addr;
1601 pmd_t *src_pmd, *dst_pmd;
1602 long err = -EINVAL;
1603 ssize_t moved = 0;
1604
1605 /* Sanitize the command parameters. */
1606 if (WARN_ON_ONCE(src_start & ~PAGE_MASK) ||
1607 WARN_ON_ONCE(dst_start & ~PAGE_MASK) ||
1608 WARN_ON_ONCE(len & ~PAGE_MASK))
1609 goto out;
1610
1611 /* Does the address range wrap, or is the span zero-sized? */
1612 if (WARN_ON_ONCE(src_start + len <= src_start) ||
1613 WARN_ON_ONCE(dst_start + len <= dst_start))
1614 goto out;
1615
1616 err = uffd_move_lock(mm, dst_start, src_start, &dst_vma, &src_vma);
1617 if (err)
1618 goto out;
1619
1620 /* Re-check after taking map_changing_lock */
1621 err = -EAGAIN;
1622 down_read(&ctx->map_changing_lock);
1623 if (likely(atomic_read(&ctx->mmap_changing)))
1624 goto out_unlock;
1625 /*
1626 * Make sure the vma is not shared, that the src and dst remap
1627 * ranges are both valid and fully within a single existing
1628 * vma.
1629 */
1630 err = -EINVAL;
1631 if (src_vma->vm_flags & VM_SHARED)
1632 goto out_unlock;
1633 if (src_start + len > src_vma->vm_end)
1634 goto out_unlock;
1635
1636 if (dst_vma->vm_flags & VM_SHARED)
1637 goto out_unlock;
1638 if (dst_start + len > dst_vma->vm_end)
1639 goto out_unlock;
1640
1641 err = validate_move_areas(ctx, src_vma, dst_vma);
1642 if (err)
1643 goto out_unlock;
1644
1645 for (src_addr = src_start, dst_addr = dst_start;
1646 src_addr < src_start + len;) {
1647 spinlock_t *ptl;
1648 pmd_t dst_pmdval;
1649 unsigned long step_size;
1650
1651 /*
1652 * Below works because anonymous area would not have a
1653 * transparent huge PUD. If file-backed support is added,
1654 * that case would need to be handled here.
1655 */
1656 src_pmd = mm_find_pmd(mm, src_addr);
1657 if (unlikely(!src_pmd)) {
1658 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
1659 err = -ENOENT;
1660 break;
1661 }
1662 src_pmd = mm_alloc_pmd(mm, src_addr);
1663 if (unlikely(!src_pmd)) {
1664 err = -ENOMEM;
1665 break;
1666 }
1667 }
1668 dst_pmd = mm_alloc_pmd(mm, dst_addr);
1669 if (unlikely(!dst_pmd)) {
1670 err = -ENOMEM;
1671 break;
1672 }
1673
1674 dst_pmdval = pmdp_get_lockless(dst_pmd);
1675 /*
1676 * If the dst_pmd is mapped as THP don't override it and just
1677 * be strict. If dst_pmd changes into TPH after this check, the
1678 * move_pages_huge_pmd() will detect the change and retry
1679 * while move_pages_pte() will detect the change and fail.
1680 */
1681 if (unlikely(pmd_trans_huge(dst_pmdval))) {
1682 err = -EEXIST;
1683 break;
1684 }
1685
1686 ptl = pmd_trans_huge_lock(src_pmd, src_vma);
1687 if (ptl) {
1688 if (pmd_devmap(*src_pmd)) {
1689 spin_unlock(ptl);
1690 err = -ENOENT;
1691 break;
1692 }
1693
1694 /* Check if we can move the pmd without splitting it. */
1695 if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
1696 !pmd_none(dst_pmdval)) {
1697 struct folio *folio = pmd_folio(*src_pmd);
1698
1699 if (!folio || (!is_huge_zero_folio(folio) &&
1700 !PageAnonExclusive(&folio->page))) {
1701 spin_unlock(ptl);
1702 err = -EBUSY;
1703 break;
1704 }
1705
1706 spin_unlock(ptl);
1707 split_huge_pmd(src_vma, src_pmd, src_addr);
1708 /* The folio will be split by move_pages_pte() */
1709 continue;
1710 }
1711
1712 err = move_pages_huge_pmd(mm, dst_pmd, src_pmd,
1713 dst_pmdval, dst_vma, src_vma,
1714 dst_addr, src_addr);
1715 step_size = HPAGE_PMD_SIZE;
1716 } else {
1717 if (pmd_none(*src_pmd)) {
1718 if (!(mode & UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES)) {
1719 err = -ENOENT;
1720 break;
1721 }
1722 if (unlikely(__pte_alloc(mm, src_pmd))) {
1723 err = -ENOMEM;
1724 break;
1725 }
1726 }
1727
1728 if (unlikely(pte_alloc(mm, dst_pmd))) {
1729 err = -ENOMEM;
1730 break;
1731 }
1732
1733 err = move_pages_pte(mm, dst_pmd, src_pmd,
1734 dst_vma, src_vma,
1735 dst_addr, src_addr, mode);
1736 step_size = PAGE_SIZE;
1737 }
1738
1739 cond_resched();
1740
1741 if (fatal_signal_pending(current)) {
1742 /* Do not override an error */
1743 if (!err || err == -EAGAIN)
1744 err = -EINTR;
1745 break;
1746 }
1747
1748 if (err) {
1749 if (err == -EAGAIN)
1750 continue;
1751 break;
1752 }
1753
1754 /* Proceed to the next page */
1755 dst_addr += step_size;
1756 src_addr += step_size;
1757 moved += step_size;
1758 }
1759
1760 out_unlock:
1761 up_read(&ctx->map_changing_lock);
1762 uffd_move_unlock(dst_vma, src_vma);
1763 out:
1764 VM_WARN_ON(moved < 0);
1765 VM_WARN_ON(err > 0);
1766 VM_WARN_ON(!moved && !err);
1767 return moved ? moved : err;
1768 }
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