1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Device Memory Migration functionality.
4 *
5 * Originally written by Jérôme Glisse.
6 */
7#include <linux/export.h>
8#include <linux/memremap.h>
9#include <linux/migrate.h>
10#include <linux/mm.h>
11#include <linux/mm_inline.h>
12#include <linux/mmu_notifier.h>
13#include <linux/oom.h>
14#include <linux/pagewalk.h>
15#include <linux/rmap.h>
16#include <linux/swapops.h>
17#include <asm/tlbflush.h>
18#include "internal.h"
19
20static int migrate_vma_collect_skip(unsigned long start,
21 unsigned long end,
22 struct mm_walk *walk)
23{
24 struct migrate_vma *migrate = walk->private;
25 unsigned long addr;
26
27 for (addr = start; addr < end; addr += PAGE_SIZE) {
28 migrate->dst[migrate->npages] = 0;
29 migrate->src[migrate->npages++] = 0;
30 }
31
32 return 0;
33}
34
35static int migrate_vma_collect_hole(unsigned long start,
36 unsigned long end,
37 __always_unused int depth,
38 struct mm_walk *walk)
39{
40 struct migrate_vma *migrate = walk->private;
41 unsigned long addr;
42
43 /* Only allow populating anonymous memory. */
44 if (!vma_is_anonymous(vma: walk->vma))
45 return migrate_vma_collect_skip(start, end, walk);
46
47 for (addr = start; addr < end; addr += PAGE_SIZE) {
48 migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
49 migrate->dst[migrate->npages] = 0;
50 migrate->npages++;
51 migrate->cpages++;
52 }
53
54 return 0;
55}
56
57static int migrate_vma_collect_pmd(pmd_t *pmdp,
58 unsigned long start,
59 unsigned long end,
60 struct mm_walk *walk)
61{
62 struct migrate_vma *migrate = walk->private;
63 struct vm_area_struct *vma = walk->vma;
64 struct mm_struct *mm = vma->vm_mm;
65 unsigned long addr = start, unmapped = 0;
66 spinlock_t *ptl;
67 pte_t *ptep;
68
69again:
70 if (pmd_none(pmd: *pmdp))
71 return migrate_vma_collect_hole(start, end, depth: -1, walk);
72
73 if (pmd_trans_huge(pmd: *pmdp)) {
74 struct page *page;
75
76 ptl = pmd_lock(mm, pmd: pmdp);
77 if (unlikely(!pmd_trans_huge(*pmdp))) {
78 spin_unlock(lock: ptl);
79 goto again;
80 }
81
82 page = pmd_page(*pmdp);
83 if (is_huge_zero_page(page)) {
84 spin_unlock(lock: ptl);
85 split_huge_pmd(vma, pmdp, addr);
86 } else {
87 int ret;
88
89 get_page(page);
90 spin_unlock(lock: ptl);
91 if (unlikely(!trylock_page(page)))
92 return migrate_vma_collect_skip(start, end,
93 walk);
94 ret = split_huge_page(page);
95 unlock_page(page);
96 put_page(page);
97 if (ret)
98 return migrate_vma_collect_skip(start, end,
99 walk);
100 }
101 }
102
103 ptep = pte_offset_map_lock(mm, pmd: pmdp, addr, ptlp: &ptl);
104 if (!ptep)
105 goto again;
106 arch_enter_lazy_mmu_mode();
107
108 for (; addr < end; addr += PAGE_SIZE, ptep++) {
109 unsigned long mpfn = 0, pfn;
110 struct page *page;
111 swp_entry_t entry;
112 pte_t pte;
113
114 pte = ptep_get(ptep);
115
116 if (pte_none(pte)) {
117 if (vma_is_anonymous(vma)) {
118 mpfn = MIGRATE_PFN_MIGRATE;
119 migrate->cpages++;
120 }
121 goto next;
122 }
123
124 if (!pte_present(a: pte)) {
125 /*
126 * Only care about unaddressable device page special
127 * page table entry. Other special swap entries are not
128 * migratable, and we ignore regular swapped page.
129 */
130 entry = pte_to_swp_entry(pte);
131 if (!is_device_private_entry(entry))
132 goto next;
133
134 page = pfn_swap_entry_to_page(entry);
135 if (!(migrate->flags &
136 MIGRATE_VMA_SELECT_DEVICE_PRIVATE) ||
137 page->pgmap->owner != migrate->pgmap_owner)
138 goto next;
139
140 mpfn = migrate_pfn(page_to_pfn(page)) |
141 MIGRATE_PFN_MIGRATE;
142 if (is_writable_device_private_entry(entry))
143 mpfn |= MIGRATE_PFN_WRITE;
144 } else {
145 pfn = pte_pfn(pte);
146 if (is_zero_pfn(pfn) &&
147 (migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) {
148 mpfn = MIGRATE_PFN_MIGRATE;
149 migrate->cpages++;
150 goto next;
151 }
152 page = vm_normal_page(vma: migrate->vma, addr, pte);
153 if (page && !is_zone_device_page(page) &&
154 !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
155 goto next;
156 else if (page && is_device_coherent_page(page) &&
157 (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
158 page->pgmap->owner != migrate->pgmap_owner))
159 goto next;
160 mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
161 mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
162 }
163
164 /* FIXME support THP */
165 if (!page || !page->mapping || PageTransCompound(page)) {
166 mpfn = 0;
167 goto next;
168 }
169
170 /*
171 * By getting a reference on the page we pin it and that blocks
172 * any kind of migration. Side effect is that it "freezes" the
173 * pte.
174 *
175 * We drop this reference after isolating the page from the lru
176 * for non device page (device page are not on the lru and thus
177 * can't be dropped from it).
178 */
179 get_page(page);
180
181 /*
182 * We rely on trylock_page() to avoid deadlock between
183 * concurrent migrations where each is waiting on the others
184 * page lock. If we can't immediately lock the page we fail this
185 * migration as it is only best effort anyway.
186 *
187 * If we can lock the page it's safe to set up a migration entry
188 * now. In the common case where the page is mapped once in a
189 * single process setting up the migration entry now is an
190 * optimisation to avoid walking the rmap later with
191 * try_to_migrate().
192 */
193 if (trylock_page(page)) {
194 bool anon_exclusive;
195 pte_t swp_pte;
196
197 flush_cache_page(vma, vmaddr: addr, pfn: pte_pfn(pte));
198 anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
199 if (anon_exclusive) {
200 pte = ptep_clear_flush(vma, address: addr, ptep);
201
202 if (page_try_share_anon_rmap(page)) {
203 set_pte_at(mm, addr, ptep, pte);
204 unlock_page(page);
205 put_page(page);
206 mpfn = 0;
207 goto next;
208 }
209 } else {
210 pte = ptep_get_and_clear(mm, addr, ptep);
211 }
212
213 migrate->cpages++;
214
215 /* Set the dirty flag on the folio now the pte is gone. */
216 if (pte_dirty(pte))
217 folio_mark_dirty(page_folio(page));
218
219 /* Setup special migration page table entry */
220 if (mpfn & MIGRATE_PFN_WRITE)
221 entry = make_writable_migration_entry(
222 page_to_pfn(page));
223 else if (anon_exclusive)
224 entry = make_readable_exclusive_migration_entry(
225 page_to_pfn(page));
226 else
227 entry = make_readable_migration_entry(
228 page_to_pfn(page));
229 if (pte_present(a: pte)) {
230 if (pte_young(pte))
231 entry = make_migration_entry_young(entry);
232 if (pte_dirty(pte))
233 entry = make_migration_entry_dirty(entry);
234 }
235 swp_pte = swp_entry_to_pte(entry);
236 if (pte_present(a: pte)) {
237 if (pte_soft_dirty(pte))
238 swp_pte = pte_swp_mksoft_dirty(pte: swp_pte);
239 if (pte_uffd_wp(pte))
240 swp_pte = pte_swp_mkuffd_wp(pte: swp_pte);
241 } else {
242 if (pte_swp_soft_dirty(pte))
243 swp_pte = pte_swp_mksoft_dirty(pte: swp_pte);
244 if (pte_swp_uffd_wp(pte))
245 swp_pte = pte_swp_mkuffd_wp(pte: swp_pte);
246 }
247 set_pte_at(mm, addr, ptep, swp_pte);
248
249 /*
250 * This is like regular unmap: we remove the rmap and
251 * drop page refcount. Page won't be freed, as we took
252 * a reference just above.
253 */
254 page_remove_rmap(page, vma, compound: false);
255 put_page(page);
256
257 if (pte_present(a: pte))
258 unmapped++;
259 } else {
260 put_page(page);
261 mpfn = 0;
262 }
263
264next:
265 migrate->dst[migrate->npages] = 0;
266 migrate->src[migrate->npages++] = mpfn;
267 }
268
269 /* Only flush the TLB if we actually modified any entries */
270 if (unmapped)
271 flush_tlb_range(walk->vma, start, end);
272
273 arch_leave_lazy_mmu_mode();
274 pte_unmap_unlock(ptep - 1, ptl);
275
276 return 0;
277}
278
279static const struct mm_walk_ops migrate_vma_walk_ops = {
280 .pmd_entry = migrate_vma_collect_pmd,
281 .pte_hole = migrate_vma_collect_hole,
282 .walk_lock = PGWALK_RDLOCK,
283};
284
285/*
286 * migrate_vma_collect() - collect pages over a range of virtual addresses
287 * @migrate: migrate struct containing all migration information
288 *
289 * This will walk the CPU page table. For each virtual address backed by a
290 * valid page, it updates the src array and takes a reference on the page, in
291 * order to pin the page until we lock it and unmap it.
292 */
293static void migrate_vma_collect(struct migrate_vma *migrate)
294{
295 struct mmu_notifier_range range;
296
297 /*
298 * Note that the pgmap_owner is passed to the mmu notifier callback so
299 * that the registered device driver can skip invalidating device
300 * private page mappings that won't be migrated.
301 */
302 mmu_notifier_range_init_owner(range: &range, event: MMU_NOTIFY_MIGRATE, flags: 0,
303 mm: migrate->vma->vm_mm, start: migrate->start, end: migrate->end,
304 owner: migrate->pgmap_owner);
305 mmu_notifier_invalidate_range_start(range: &range);
306
307 walk_page_range(mm: migrate->vma->vm_mm, start: migrate->start, end: migrate->end,
308 ops: &migrate_vma_walk_ops, private: migrate);
309
310 mmu_notifier_invalidate_range_end(range: &range);
311 migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
312}
313
314/*
315 * migrate_vma_check_page() - check if page is pinned or not
316 * @page: struct page to check
317 *
318 * Pinned pages cannot be migrated. This is the same test as in
319 * folio_migrate_mapping(), except that here we allow migration of a
320 * ZONE_DEVICE page.
321 */
322static bool migrate_vma_check_page(struct page *page, struct page *fault_page)
323{
324 /*
325 * One extra ref because caller holds an extra reference, either from
326 * isolate_lru_page() for a regular page, or migrate_vma_collect() for
327 * a device page.
328 */
329 int extra = 1 + (page == fault_page);
330
331 /*
332 * FIXME support THP (transparent huge page), it is bit more complex to
333 * check them than regular pages, because they can be mapped with a pmd
334 * or with a pte (split pte mapping).
335 */
336 if (PageCompound(page))
337 return false;
338
339 /* Page from ZONE_DEVICE have one extra reference */
340 if (is_zone_device_page(page))
341 extra++;
342
343 /* For file back page */
344 if (page_mapping(page))
345 extra += 1 + page_has_private(page);
346
347 if ((page_count(page) - extra) > page_mapcount(page))
348 return false;
349
350 return true;
351}
352
353/*
354 * Unmaps pages for migration. Returns number of source pfns marked as
355 * migrating.
356 */
357static unsigned long migrate_device_unmap(unsigned long *src_pfns,
358 unsigned long npages,
359 struct page *fault_page)
360{
361 unsigned long i, restore = 0;
362 bool allow_drain = true;
363 unsigned long unmapped = 0;
364
365 lru_add_drain();
366
367 for (i = 0; i < npages; i++) {
368 struct page *page = migrate_pfn_to_page(mpfn: src_pfns[i]);
369 struct folio *folio;
370
371 if (!page) {
372 if (src_pfns[i] & MIGRATE_PFN_MIGRATE)
373 unmapped++;
374 continue;
375 }
376
377 /* ZONE_DEVICE pages are not on LRU */
378 if (!is_zone_device_page(page)) {
379 if (!PageLRU(page) && allow_drain) {
380 /* Drain CPU's lru cache */
381 lru_add_drain_all();
382 allow_drain = false;
383 }
384
385 if (!isolate_lru_page(page)) {
386 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
387 restore++;
388 continue;
389 }
390
391 /* Drop the reference we took in collect */
392 put_page(page);
393 }
394
395 folio = page_folio(page);
396 if (folio_mapped(folio))
397 try_to_migrate(folio, flags: 0);
398
399 if (page_mapped(page) ||
400 !migrate_vma_check_page(page, fault_page)) {
401 if (!is_zone_device_page(page)) {
402 get_page(page);
403 putback_lru_page(page);
404 }
405
406 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
407 restore++;
408 continue;
409 }
410
411 unmapped++;
412 }
413
414 for (i = 0; i < npages && restore; i++) {
415 struct page *page = migrate_pfn_to_page(mpfn: src_pfns[i]);
416 struct folio *folio;
417
418 if (!page || (src_pfns[i] & MIGRATE_PFN_MIGRATE))
419 continue;
420
421 folio = page_folio(page);
422 remove_migration_ptes(src: folio, dst: folio, locked: false);
423
424 src_pfns[i] = 0;
425 folio_unlock(folio);
426 folio_put(folio);
427 restore--;
428 }
429
430 return unmapped;
431}
432
433/*
434 * migrate_vma_unmap() - replace page mapping with special migration pte entry
435 * @migrate: migrate struct containing all migration information
436 *
437 * Isolate pages from the LRU and replace mappings (CPU page table pte) with a
438 * special migration pte entry and check if it has been pinned. Pinned pages are
439 * restored because we cannot migrate them.
440 *
441 * This is the last step before we call the device driver callback to allocate
442 * destination memory and copy contents of original page over to new page.
443 */
444static void migrate_vma_unmap(struct migrate_vma *migrate)
445{
446 migrate->cpages = migrate_device_unmap(src_pfns: migrate->src, npages: migrate->npages,
447 fault_page: migrate->fault_page);
448}
449
450/**
451 * migrate_vma_setup() - prepare to migrate a range of memory
452 * @args: contains the vma, start, and pfns arrays for the migration
453 *
454 * Returns: negative errno on failures, 0 when 0 or more pages were migrated
455 * without an error.
456 *
457 * Prepare to migrate a range of memory virtual address range by collecting all
458 * the pages backing each virtual address in the range, saving them inside the
459 * src array. Then lock those pages and unmap them. Once the pages are locked
460 * and unmapped, check whether each page is pinned or not. Pages that aren't
461 * pinned have the MIGRATE_PFN_MIGRATE flag set (by this function) in the
462 * corresponding src array entry. Then restores any pages that are pinned, by
463 * remapping and unlocking those pages.
464 *
465 * The caller should then allocate destination memory and copy source memory to
466 * it for all those entries (ie with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE
467 * flag set). Once these are allocated and copied, the caller must update each
468 * corresponding entry in the dst array with the pfn value of the destination
469 * page and with MIGRATE_PFN_VALID. Destination pages must be locked via
470 * lock_page().
471 *
472 * Note that the caller does not have to migrate all the pages that are marked
473 * with MIGRATE_PFN_MIGRATE flag in src array unless this is a migration from
474 * device memory to system memory. If the caller cannot migrate a device page
475 * back to system memory, then it must return VM_FAULT_SIGBUS, which has severe
476 * consequences for the userspace process, so it must be avoided if at all
477 * possible.
478 *
479 * For empty entries inside CPU page table (pte_none() or pmd_none() is true) we
480 * do set MIGRATE_PFN_MIGRATE flag inside the corresponding source array thus
481 * allowing the caller to allocate device memory for those unbacked virtual
482 * addresses. For this the caller simply has to allocate device memory and
483 * properly set the destination entry like for regular migration. Note that
484 * this can still fail, and thus inside the device driver you must check if the
485 * migration was successful for those entries after calling migrate_vma_pages(),
486 * just like for regular migration.
487 *
488 * After that, the callers must call migrate_vma_pages() to go over each entry
489 * in the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
490 * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
491 * then migrate_vma_pages() to migrate struct page information from the source
492 * struct page to the destination struct page. If it fails to migrate the
493 * struct page information, then it clears the MIGRATE_PFN_MIGRATE flag in the
494 * src array.
495 *
496 * At this point all successfully migrated pages have an entry in the src
497 * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
498 * array entry with MIGRATE_PFN_VALID flag set.
499 *
500 * Once migrate_vma_pages() returns the caller may inspect which pages were
501 * successfully migrated, and which were not. Successfully migrated pages will
502 * have the MIGRATE_PFN_MIGRATE flag set for their src array entry.
503 *
504 * It is safe to update device page table after migrate_vma_pages() because
505 * both destination and source page are still locked, and the mmap_lock is held
506 * in read mode (hence no one can unmap the range being migrated).
507 *
508 * Once the caller is done cleaning up things and updating its page table (if it
509 * chose to do so, this is not an obligation) it finally calls
510 * migrate_vma_finalize() to update the CPU page table to point to new pages
511 * for successfully migrated pages or otherwise restore the CPU page table to
512 * point to the original source pages.
513 */
514int migrate_vma_setup(struct migrate_vma *args)
515{
516 long nr_pages = (args->end - args->start) >> PAGE_SHIFT;
517
518 args->start &= PAGE_MASK;
519 args->end &= PAGE_MASK;
520 if (!args->vma || is_vm_hugetlb_page(vma: args->vma) ||
521 (args->vma->vm_flags & VM_SPECIAL) || vma_is_dax(vma: args->vma))
522 return -EINVAL;
523 if (nr_pages <= 0)
524 return -EINVAL;
525 if (args->start < args->vma->vm_start ||
526 args->start >= args->vma->vm_end)
527 return -EINVAL;
528 if (args->end <= args->vma->vm_start || args->end > args->vma->vm_end)
529 return -EINVAL;
530 if (!args->src || !args->dst)
531 return -EINVAL;
532 if (args->fault_page && !is_device_private_page(page: args->fault_page))
533 return -EINVAL;
534
535 memset(args->src, 0, sizeof(*args->src) * nr_pages);
536 args->cpages = 0;
537 args->npages = 0;
538
539 migrate_vma_collect(migrate: args);
540
541 if (args->cpages)
542 migrate_vma_unmap(migrate: args);
543
544 /*
545 * At this point pages are locked and unmapped, and thus they have
546 * stable content and can safely be copied to destination memory that
547 * is allocated by the drivers.
548 */
549 return 0;
550
551}
552EXPORT_SYMBOL(migrate_vma_setup);
553
554/*
555 * This code closely matches the code in:
556 * __handle_mm_fault()
557 * handle_pte_fault()
558 * do_anonymous_page()
559 * to map in an anonymous zero page but the struct page will be a ZONE_DEVICE
560 * private or coherent page.
561 */
562static void migrate_vma_insert_page(struct migrate_vma *migrate,
563 unsigned long addr,
564 struct page *page,
565 unsigned long *src)
566{
567 struct vm_area_struct *vma = migrate->vma;
568 struct mm_struct *mm = vma->vm_mm;
569 bool flush = false;
570 spinlock_t *ptl;
571 pte_t entry;
572 pgd_t *pgdp;
573 p4d_t *p4dp;
574 pud_t *pudp;
575 pmd_t *pmdp;
576 pte_t *ptep;
577 pte_t orig_pte;
578
579 /* Only allow populating anonymous memory */
580 if (!vma_is_anonymous(vma))
581 goto abort;
582
583 pgdp = pgd_offset(mm, addr);
584 p4dp = p4d_alloc(mm, pgd: pgdp, address: addr);
585 if (!p4dp)
586 goto abort;
587 pudp = pud_alloc(mm, p4d: p4dp, address: addr);
588 if (!pudp)
589 goto abort;
590 pmdp = pmd_alloc(mm, pud: pudp, address: addr);
591 if (!pmdp)
592 goto abort;
593 if (pmd_trans_huge(pmd: *pmdp) || pmd_devmap(pmd: *pmdp))
594 goto abort;
595 if (pte_alloc(mm, pmdp))
596 goto abort;
597 if (unlikely(anon_vma_prepare(vma)))
598 goto abort;
599 if (mem_cgroup_charge(page_folio(page), mm: vma->vm_mm, GFP_KERNEL))
600 goto abort;
601
602 /*
603 * The memory barrier inside __SetPageUptodate makes sure that
604 * preceding stores to the page contents become visible before
605 * the set_pte_at() write.
606 */
607 __SetPageUptodate(page);
608
609 if (is_device_private_page(page)) {
610 swp_entry_t swp_entry;
611
612 if (vma->vm_flags & VM_WRITE)
613 swp_entry = make_writable_device_private_entry(
614 page_to_pfn(page));
615 else
616 swp_entry = make_readable_device_private_entry(
617 page_to_pfn(page));
618 entry = swp_entry_to_pte(entry: swp_entry);
619 } else {
620 if (is_zone_device_page(page) &&
621 !is_device_coherent_page(page)) {
622 pr_warn_once("Unsupported ZONE_DEVICE page type.\n");
623 goto abort;
624 }
625 entry = mk_pte(page, vma->vm_page_prot);
626 if (vma->vm_flags & VM_WRITE)
627 entry = pte_mkwrite(pte: pte_mkdirty(pte: entry), vma);
628 }
629
630 ptep = pte_offset_map_lock(mm, pmd: pmdp, addr, ptlp: &ptl);
631 if (!ptep)
632 goto abort;
633 orig_pte = ptep_get(ptep);
634
635 if (check_stable_address_space(mm))
636 goto unlock_abort;
637
638 if (pte_present(a: orig_pte)) {
639 unsigned long pfn = pte_pfn(pte: orig_pte);
640
641 if (!is_zero_pfn(pfn))
642 goto unlock_abort;
643 flush = true;
644 } else if (!pte_none(pte: orig_pte))
645 goto unlock_abort;
646
647 /*
648 * Check for userfaultfd but do not deliver the fault. Instead,
649 * just back off.
650 */
651 if (userfaultfd_missing(vma))
652 goto unlock_abort;
653
654 inc_mm_counter(mm, member: MM_ANONPAGES);
655 page_add_new_anon_rmap(page, vma, address: addr);
656 if (!is_zone_device_page(page))
657 lru_cache_add_inactive_or_unevictable(page, vma);
658 get_page(page);
659
660 if (flush) {
661 flush_cache_page(vma, vmaddr: addr, pfn: pte_pfn(pte: orig_pte));
662 ptep_clear_flush(vma, address: addr, ptep);
663 set_pte_at_notify(mm, addr, ptep, entry);
664 update_mmu_cache(vma, addr, ptep);
665 } else {
666 /* No need to invalidate - it was non-present before */
667 set_pte_at(mm, addr, ptep, entry);
668 update_mmu_cache(vma, addr, ptep);
669 }
670
671 pte_unmap_unlock(ptep, ptl);
672 *src = MIGRATE_PFN_MIGRATE;
673 return;
674
675unlock_abort:
676 pte_unmap_unlock(ptep, ptl);
677abort:
678 *src &= ~MIGRATE_PFN_MIGRATE;
679}
680
681static void __migrate_device_pages(unsigned long *src_pfns,
682 unsigned long *dst_pfns, unsigned long npages,
683 struct migrate_vma *migrate)
684{
685 struct mmu_notifier_range range;
686 unsigned long i;
687 bool notified = false;
688
689 for (i = 0; i < npages; i++) {
690 struct page *newpage = migrate_pfn_to_page(mpfn: dst_pfns[i]);
691 struct page *page = migrate_pfn_to_page(mpfn: src_pfns[i]);
692 struct address_space *mapping;
693 int r;
694
695 if (!newpage) {
696 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
697 continue;
698 }
699
700 if (!page) {
701 unsigned long addr;
702
703 if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE))
704 continue;
705
706 /*
707 * The only time there is no vma is when called from
708 * migrate_device_coherent_page(). However this isn't
709 * called if the page could not be unmapped.
710 */
711 VM_BUG_ON(!migrate);
712 addr = migrate->start + i*PAGE_SIZE;
713 if (!notified) {
714 notified = true;
715
716 mmu_notifier_range_init_owner(range: &range,
717 event: MMU_NOTIFY_MIGRATE, flags: 0,
718 mm: migrate->vma->vm_mm, start: addr, end: migrate->end,
719 owner: migrate->pgmap_owner);
720 mmu_notifier_invalidate_range_start(range: &range);
721 }
722 migrate_vma_insert_page(migrate, addr, page: newpage,
723 src: &src_pfns[i]);
724 continue;
725 }
726
727 mapping = page_mapping(page);
728
729 if (is_device_private_page(page: newpage) ||
730 is_device_coherent_page(page: newpage)) {
731 if (mapping) {
732 struct folio *folio;
733
734 folio = page_folio(page);
735
736 /*
737 * For now only support anonymous memory migrating to
738 * device private or coherent memory.
739 *
740 * Try to get rid of swap cache if possible.
741 */
742 if (!folio_test_anon(folio) ||
743 !folio_free_swap(folio)) {
744 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
745 continue;
746 }
747 }
748 } else if (is_zone_device_page(page: newpage)) {
749 /*
750 * Other types of ZONE_DEVICE page are not supported.
751 */
752 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
753 continue;
754 }
755
756 if (migrate && migrate->fault_page == page)
757 r = migrate_folio_extra(mapping, page_folio(newpage),
758 page_folio(page),
759 mode: MIGRATE_SYNC_NO_COPY, extra_count: 1);
760 else
761 r = migrate_folio(mapping, page_folio(newpage),
762 page_folio(page), mode: MIGRATE_SYNC_NO_COPY);
763 if (r != MIGRATEPAGE_SUCCESS)
764 src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
765 }
766
767 if (notified)
768 mmu_notifier_invalidate_range_end(range: &range);
769}
770
771/**
772 * migrate_device_pages() - migrate meta-data from src page to dst page
773 * @src_pfns: src_pfns returned from migrate_device_range()
774 * @dst_pfns: array of pfns allocated by the driver to migrate memory to
775 * @npages: number of pages in the range
776 *
777 * Equivalent to migrate_vma_pages(). This is called to migrate struct page
778 * meta-data from source struct page to destination.
779 */
780void migrate_device_pages(unsigned long *src_pfns, unsigned long *dst_pfns,
781 unsigned long npages)
782{
783 __migrate_device_pages(src_pfns, dst_pfns, npages, NULL);
784}
785EXPORT_SYMBOL(migrate_device_pages);
786
787/**
788 * migrate_vma_pages() - migrate meta-data from src page to dst page
789 * @migrate: migrate struct containing all migration information
790 *
791 * This migrates struct page meta-data from source struct page to destination
792 * struct page. This effectively finishes the migration from source page to the
793 * destination page.
794 */
795void migrate_vma_pages(struct migrate_vma *migrate)
796{
797 __migrate_device_pages(src_pfns: migrate->src, dst_pfns: migrate->dst, npages: migrate->npages, migrate);
798}
799EXPORT_SYMBOL(migrate_vma_pages);
800
801/*
802 * migrate_device_finalize() - complete page migration
803 * @src_pfns: src_pfns returned from migrate_device_range()
804 * @dst_pfns: array of pfns allocated by the driver to migrate memory to
805 * @npages: number of pages in the range
806 *
807 * Completes migration of the page by removing special migration entries.
808 * Drivers must ensure copying of page data is complete and visible to the CPU
809 * before calling this.
810 */
811void migrate_device_finalize(unsigned long *src_pfns,
812 unsigned long *dst_pfns, unsigned long npages)
813{
814 unsigned long i;
815
816 for (i = 0; i < npages; i++) {
817 struct folio *dst, *src;
818 struct page *newpage = migrate_pfn_to_page(mpfn: dst_pfns[i]);
819 struct page *page = migrate_pfn_to_page(mpfn: src_pfns[i]);
820
821 if (!page) {
822 if (newpage) {
823 unlock_page(page: newpage);
824 put_page(page: newpage);
825 }
826 continue;
827 }
828
829 if (!(src_pfns[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
830 if (newpage) {
831 unlock_page(page: newpage);
832 put_page(page: newpage);
833 }
834 newpage = page;
835 }
836
837 src = page_folio(page);
838 dst = page_folio(newpage);
839 remove_migration_ptes(src, dst, locked: false);
840 folio_unlock(folio: src);
841
842 if (is_zone_device_page(page))
843 put_page(page);
844 else
845 putback_lru_page(page);
846
847 if (newpage != page) {
848 unlock_page(page: newpage);
849 if (is_zone_device_page(page: newpage))
850 put_page(page: newpage);
851 else
852 putback_lru_page(page: newpage);
853 }
854 }
855}
856EXPORT_SYMBOL(migrate_device_finalize);
857
858/**
859 * migrate_vma_finalize() - restore CPU page table entry
860 * @migrate: migrate struct containing all migration information
861 *
862 * This replaces the special migration pte entry with either a mapping to the
863 * new page if migration was successful for that page, or to the original page
864 * otherwise.
865 *
866 * This also unlocks the pages and puts them back on the lru, or drops the extra
867 * refcount, for device pages.
868 */
869void migrate_vma_finalize(struct migrate_vma *migrate)
870{
871 migrate_device_finalize(migrate->src, migrate->dst, migrate->npages);
872}
873EXPORT_SYMBOL(migrate_vma_finalize);
874
875/**
876 * migrate_device_range() - migrate device private pfns to normal memory.
877 * @src_pfns: array large enough to hold migrating source device private pfns.
878 * @start: starting pfn in the range to migrate.
879 * @npages: number of pages to migrate.
880 *
881 * migrate_vma_setup() is similar in concept to migrate_vma_setup() except that
882 * instead of looking up pages based on virtual address mappings a range of
883 * device pfns that should be migrated to system memory is used instead.
884 *
885 * This is useful when a driver needs to free device memory but doesn't know the
886 * virtual mappings of every page that may be in device memory. For example this
887 * is often the case when a driver is being unloaded or unbound from a device.
888 *
889 * Like migrate_vma_setup() this function will take a reference and lock any
890 * migrating pages that aren't free before unmapping them. Drivers may then
891 * allocate destination pages and start copying data from the device to CPU
892 * memory before calling migrate_device_pages().
893 */
894int migrate_device_range(unsigned long *src_pfns, unsigned long start,
895 unsigned long npages)
896{
897 unsigned long i, pfn;
898
899 for (pfn = start, i = 0; i < npages; pfn++, i++) {
900 struct page *page = pfn_to_page(pfn);
901
902 if (!get_page_unless_zero(page)) {
903 src_pfns[i] = 0;
904 continue;
905 }
906
907 if (!trylock_page(page)) {
908 src_pfns[i] = 0;
909 put_page(page);
910 continue;
911 }
912
913 src_pfns[i] = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
914 }
915
916 migrate_device_unmap(src_pfns, npages, NULL);
917
918 return 0;
919}
920EXPORT_SYMBOL(migrate_device_range);
921
922/*
923 * Migrate a device coherent page back to normal memory. The caller should have
924 * a reference on page which will be copied to the new page if migration is
925 * successful or dropped on failure.
926 */
927int migrate_device_coherent_page(struct page *page)
928{
929 unsigned long src_pfn, dst_pfn = 0;
930 struct page *dpage;
931
932 WARN_ON_ONCE(PageCompound(page));
933
934 lock_page(page);
935 src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
936
937 /*
938 * We don't have a VMA and don't need to walk the page tables to find
939 * the source page. So call migrate_vma_unmap() directly to unmap the
940 * page as migrate_vma_setup() will fail if args.vma == NULL.
941 */
942 migrate_device_unmap(src_pfns: &src_pfn, npages: 1, NULL);
943 if (!(src_pfn & MIGRATE_PFN_MIGRATE))
944 return -EBUSY;
945
946 dpage = alloc_page(GFP_USER | __GFP_NOWARN);
947 if (dpage) {
948 lock_page(page: dpage);
949 dst_pfn = migrate_pfn(page_to_pfn(dpage));
950 }
951
952 migrate_device_pages(&src_pfn, &dst_pfn, 1);
953 if (src_pfn & MIGRATE_PFN_MIGRATE)
954 copy_highpage(to: dpage, from: page);
955 migrate_device_finalize(&src_pfn, &dst_pfn, 1);
956
957 if (src_pfn & MIGRATE_PFN_MIGRATE)
958 return 0;
959 return -EBUSY;
960}
961

source code of linux/mm/migrate_device.c