f7e4bfdc13b780137d08fa522b070e7192056f24
[sfrench/cifs-2.6.git] / mm / migrate.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Memory Migration functionality - linux/mm/migrate.c
4  *
5  * Copyright (C) 2006 Silicon Graphics, Inc., Christoph Lameter
6  *
7  * Page migration was first developed in the context of the memory hotplug
8  * project. The main authors of the migration code are:
9  *
10  * IWAMOTO Toshihiro <iwamoto@valinux.co.jp>
11  * Hirokazu Takahashi <taka@valinux.co.jp>
12  * Dave Hansen <haveblue@us.ibm.com>
13  * Christoph Lameter
14  */
15
16 #include <linux/migrate.h>
17 #include <linux/export.h>
18 #include <linux/swap.h>
19 #include <linux/swapops.h>
20 #include <linux/pagemap.h>
21 #include <linux/buffer_head.h>
22 #include <linux/mm_inline.h>
23 #include <linux/nsproxy.h>
24 #include <linux/pagevec.h>
25 #include <linux/ksm.h>
26 #include <linux/rmap.h>
27 #include <linux/topology.h>
28 #include <linux/cpu.h>
29 #include <linux/cpuset.h>
30 #include <linux/writeback.h>
31 #include <linux/mempolicy.h>
32 #include <linux/vmalloc.h>
33 #include <linux/security.h>
34 #include <linux/backing-dev.h>
35 #include <linux/compaction.h>
36 #include <linux/syscalls.h>
37 #include <linux/compat.h>
38 #include <linux/hugetlb.h>
39 #include <linux/hugetlb_cgroup.h>
40 #include <linux/gfp.h>
41 #include <linux/pfn_t.h>
42 #include <linux/memremap.h>
43 #include <linux/userfaultfd_k.h>
44 #include <linux/balloon_compaction.h>
45 #include <linux/mmu_notifier.h>
46 #include <linux/page_idle.h>
47 #include <linux/page_owner.h>
48 #include <linux/sched/mm.h>
49 #include <linux/ptrace.h>
50
51 #include <asm/tlbflush.h>
52
53 #define CREATE_TRACE_POINTS
54 #include <trace/events/migrate.h>
55
56 #include "internal.h"
57
58 /*
59  * migrate_prep() needs to be called before we start compiling a list of pages
60  * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
61  * undesirable, use migrate_prep_local()
62  */
63 int migrate_prep(void)
64 {
65         /*
66          * Clear the LRU lists so pages can be isolated.
67          * Note that pages may be moved off the LRU after we have
68          * drained them. Those pages will fail to migrate like other
69          * pages that may be busy.
70          */
71         lru_add_drain_all();
72
73         return 0;
74 }
75
76 /* Do the necessary work of migrate_prep but not if it involves other CPUs */
77 int migrate_prep_local(void)
78 {
79         lru_add_drain();
80
81         return 0;
82 }
83
84 int isolate_movable_page(struct page *page, isolate_mode_t mode)
85 {
86         struct address_space *mapping;
87
88         /*
89          * Avoid burning cycles with pages that are yet under __free_pages(),
90          * or just got freed under us.
91          *
92          * In case we 'win' a race for a movable page being freed under us and
93          * raise its refcount preventing __free_pages() from doing its job
94          * the put_page() at the end of this block will take care of
95          * release this page, thus avoiding a nasty leakage.
96          */
97         if (unlikely(!get_page_unless_zero(page)))
98                 goto out;
99
100         /*
101          * Check PageMovable before holding a PG_lock because page's owner
102          * assumes anybody doesn't touch PG_lock of newly allocated page
103          * so unconditionally grapping the lock ruins page's owner side.
104          */
105         if (unlikely(!__PageMovable(page)))
106                 goto out_putpage;
107         /*
108          * As movable pages are not isolated from LRU lists, concurrent
109          * compaction threads can race against page migration functions
110          * as well as race against the releasing a page.
111          *
112          * In order to avoid having an already isolated movable page
113          * being (wrongly) re-isolated while it is under migration,
114          * or to avoid attempting to isolate pages being released,
115          * lets be sure we have the page lock
116          * before proceeding with the movable page isolation steps.
117          */
118         if (unlikely(!trylock_page(page)))
119                 goto out_putpage;
120
121         if (!PageMovable(page) || PageIsolated(page))
122                 goto out_no_isolated;
123
124         mapping = page_mapping(page);
125         VM_BUG_ON_PAGE(!mapping, page);
126
127         if (!mapping->a_ops->isolate_page(page, mode))
128                 goto out_no_isolated;
129
130         /* Driver shouldn't use PG_isolated bit of page->flags */
131         WARN_ON_ONCE(PageIsolated(page));
132         __SetPageIsolated(page);
133         unlock_page(page);
134
135         return 0;
136
137 out_no_isolated:
138         unlock_page(page);
139 out_putpage:
140         put_page(page);
141 out:
142         return -EBUSY;
143 }
144
145 /* It should be called on page which is PG_movable */
146 void putback_movable_page(struct page *page)
147 {
148         struct address_space *mapping;
149
150         VM_BUG_ON_PAGE(!PageLocked(page), page);
151         VM_BUG_ON_PAGE(!PageMovable(page), page);
152         VM_BUG_ON_PAGE(!PageIsolated(page), page);
153
154         mapping = page_mapping(page);
155         mapping->a_ops->putback_page(page);
156         __ClearPageIsolated(page);
157 }
158
159 /*
160  * Put previously isolated pages back onto the appropriate lists
161  * from where they were once taken off for compaction/migration.
162  *
163  * This function shall be used whenever the isolated pageset has been
164  * built from lru, balloon, hugetlbfs page. See isolate_migratepages_range()
165  * and isolate_huge_page().
166  */
167 void putback_movable_pages(struct list_head *l)
168 {
169         struct page *page;
170         struct page *page2;
171
172         list_for_each_entry_safe(page, page2, l, lru) {
173                 if (unlikely(PageHuge(page))) {
174                         putback_active_hugepage(page);
175                         continue;
176                 }
177                 list_del(&page->lru);
178                 /*
179                  * We isolated non-lru movable page so here we can use
180                  * __PageMovable because LRU page's mapping cannot have
181                  * PAGE_MAPPING_MOVABLE.
182                  */
183                 if (unlikely(__PageMovable(page))) {
184                         VM_BUG_ON_PAGE(!PageIsolated(page), page);
185                         lock_page(page);
186                         if (PageMovable(page))
187                                 putback_movable_page(page);
188                         else
189                                 __ClearPageIsolated(page);
190                         unlock_page(page);
191                         put_page(page);
192                 } else {
193                         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
194                                         page_is_file_cache(page), -hpage_nr_pages(page));
195                         putback_lru_page(page);
196                 }
197         }
198 }
199
200 /*
201  * Restore a potential migration pte to a working pte entry
202  */
203 static bool remove_migration_pte(struct page *page, struct vm_area_struct *vma,
204                                  unsigned long addr, void *old)
205 {
206         struct page_vma_mapped_walk pvmw = {
207                 .page = old,
208                 .vma = vma,
209                 .address = addr,
210                 .flags = PVMW_SYNC | PVMW_MIGRATION,
211         };
212         struct page *new;
213         pte_t pte;
214         swp_entry_t entry;
215
216         VM_BUG_ON_PAGE(PageTail(page), page);
217         while (page_vma_mapped_walk(&pvmw)) {
218                 if (PageKsm(page))
219                         new = page;
220                 else
221                         new = page - pvmw.page->index +
222                                 linear_page_index(vma, pvmw.address);
223
224 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
225                 /* PMD-mapped THP migration entry */
226                 if (!pvmw.pte) {
227                         VM_BUG_ON_PAGE(PageHuge(page) || !PageTransCompound(page), page);
228                         remove_migration_pmd(&pvmw, new);
229                         continue;
230                 }
231 #endif
232
233                 get_page(new);
234                 pte = pte_mkold(mk_pte(new, READ_ONCE(vma->vm_page_prot)));
235                 if (pte_swp_soft_dirty(*pvmw.pte))
236                         pte = pte_mksoft_dirty(pte);
237
238                 /*
239                  * Recheck VMA as permissions can change since migration started
240                  */
241                 entry = pte_to_swp_entry(*pvmw.pte);
242                 if (is_write_migration_entry(entry))
243                         pte = maybe_mkwrite(pte, vma);
244
245                 if (unlikely(is_zone_device_page(new))) {
246                         if (is_device_private_page(new)) {
247                                 entry = make_device_private_entry(new, pte_write(pte));
248                                 pte = swp_entry_to_pte(entry);
249                         } else if (is_device_public_page(new)) {
250                                 pte = pte_mkdevmap(pte);
251                                 flush_dcache_page(new);
252                         }
253                 } else
254                         flush_dcache_page(new);
255
256 #ifdef CONFIG_HUGETLB_PAGE
257                 if (PageHuge(new)) {
258                         pte = pte_mkhuge(pte);
259                         pte = arch_make_huge_pte(pte, vma, new, 0);
260                         set_huge_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
261                         if (PageAnon(new))
262                                 hugepage_add_anon_rmap(new, vma, pvmw.address);
263                         else
264                                 page_dup_rmap(new, true);
265                 } else
266 #endif
267                 {
268                         set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
269
270                         if (PageAnon(new))
271                                 page_add_anon_rmap(new, vma, pvmw.address, false);
272                         else
273                                 page_add_file_rmap(new, false);
274                 }
275                 if (vma->vm_flags & VM_LOCKED && !PageTransCompound(new))
276                         mlock_vma_page(new);
277
278                 if (PageTransHuge(page) && PageMlocked(page))
279                         clear_page_mlock(page);
280
281                 /* No need to invalidate - it was non-present before */
282                 update_mmu_cache(vma, pvmw.address, pvmw.pte);
283         }
284
285         return true;
286 }
287
288 /*
289  * Get rid of all migration entries and replace them by
290  * references to the indicated page.
291  */
292 void remove_migration_ptes(struct page *old, struct page *new, bool locked)
293 {
294         struct rmap_walk_control rwc = {
295                 .rmap_one = remove_migration_pte,
296                 .arg = old,
297         };
298
299         if (locked)
300                 rmap_walk_locked(new, &rwc);
301         else
302                 rmap_walk(new, &rwc);
303 }
304
305 /*
306  * Something used the pte of a page under migration. We need to
307  * get to the page and wait until migration is finished.
308  * When we return from this function the fault will be retried.
309  */
310 void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
311                                 spinlock_t *ptl)
312 {
313         pte_t pte;
314         swp_entry_t entry;
315         struct page *page;
316
317         spin_lock(ptl);
318         pte = *ptep;
319         if (!is_swap_pte(pte))
320                 goto out;
321
322         entry = pte_to_swp_entry(pte);
323         if (!is_migration_entry(entry))
324                 goto out;
325
326         page = migration_entry_to_page(entry);
327
328         /*
329          * Once page cache replacement of page migration started, page_count
330          * *must* be zero. And, we don't want to call wait_on_page_locked()
331          * against a page without get_page().
332          * So, we use get_page_unless_zero(), here. Even failed, page fault
333          * will occur again.
334          */
335         if (!get_page_unless_zero(page))
336                 goto out;
337         pte_unmap_unlock(ptep, ptl);
338         wait_on_page_locked(page);
339         put_page(page);
340         return;
341 out:
342         pte_unmap_unlock(ptep, ptl);
343 }
344
345 void migration_entry_wait(struct mm_struct *mm, pmd_t *pmd,
346                                 unsigned long address)
347 {
348         spinlock_t *ptl = pte_lockptr(mm, pmd);
349         pte_t *ptep = pte_offset_map(pmd, address);
350         __migration_entry_wait(mm, ptep, ptl);
351 }
352
353 void migration_entry_wait_huge(struct vm_area_struct *vma,
354                 struct mm_struct *mm, pte_t *pte)
355 {
356         spinlock_t *ptl = huge_pte_lockptr(hstate_vma(vma), mm, pte);
357         __migration_entry_wait(mm, pte, ptl);
358 }
359
360 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
361 void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
362 {
363         spinlock_t *ptl;
364         struct page *page;
365
366         ptl = pmd_lock(mm, pmd);
367         if (!is_pmd_migration_entry(*pmd))
368                 goto unlock;
369         page = migration_entry_to_page(pmd_to_swp_entry(*pmd));
370         if (!get_page_unless_zero(page))
371                 goto unlock;
372         spin_unlock(ptl);
373         wait_on_page_locked(page);
374         put_page(page);
375         return;
376 unlock:
377         spin_unlock(ptl);
378 }
379 #endif
380
381 #ifdef CONFIG_BLOCK
382 /* Returns true if all buffers are successfully locked */
383 static bool buffer_migrate_lock_buffers(struct buffer_head *head,
384                                                         enum migrate_mode mode)
385 {
386         struct buffer_head *bh = head;
387
388         /* Simple case, sync compaction */
389         if (mode != MIGRATE_ASYNC) {
390                 do {
391                         get_bh(bh);
392                         lock_buffer(bh);
393                         bh = bh->b_this_page;
394
395                 } while (bh != head);
396
397                 return true;
398         }
399
400         /* async case, we cannot block on lock_buffer so use trylock_buffer */
401         do {
402                 get_bh(bh);
403                 if (!trylock_buffer(bh)) {
404                         /*
405                          * We failed to lock the buffer and cannot stall in
406                          * async migration. Release the taken locks
407                          */
408                         struct buffer_head *failed_bh = bh;
409                         put_bh(failed_bh);
410                         bh = head;
411                         while (bh != failed_bh) {
412                                 unlock_buffer(bh);
413                                 put_bh(bh);
414                                 bh = bh->b_this_page;
415                         }
416                         return false;
417                 }
418
419                 bh = bh->b_this_page;
420         } while (bh != head);
421         return true;
422 }
423 #else
424 static inline bool buffer_migrate_lock_buffers(struct buffer_head *head,
425                                                         enum migrate_mode mode)
426 {
427         return true;
428 }
429 #endif /* CONFIG_BLOCK */
430
431 /*
432  * Replace the page in the mapping.
433  *
434  * The number of remaining references must be:
435  * 1 for anonymous pages without a mapping
436  * 2 for pages with a mapping
437  * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
438  */
439 int migrate_page_move_mapping(struct address_space *mapping,
440                 struct page *newpage, struct page *page,
441                 struct buffer_head *head, enum migrate_mode mode,
442                 int extra_count)
443 {
444         XA_STATE(xas, &mapping->i_pages, page_index(page));
445         struct zone *oldzone, *newzone;
446         int dirty;
447         int expected_count = 1 + extra_count;
448
449         /*
450          * Device public or private pages have an extra refcount as they are
451          * ZONE_DEVICE pages.
452          */
453         expected_count += is_device_private_page(page);
454         expected_count += is_device_public_page(page);
455
456         if (!mapping) {
457                 /* Anonymous page without mapping */
458                 if (page_count(page) != expected_count)
459                         return -EAGAIN;
460
461                 /* No turning back from here */
462                 newpage->index = page->index;
463                 newpage->mapping = page->mapping;
464                 if (PageSwapBacked(page))
465                         __SetPageSwapBacked(newpage);
466
467                 return MIGRATEPAGE_SUCCESS;
468         }
469
470         oldzone = page_zone(page);
471         newzone = page_zone(newpage);
472
473         xas_lock_irq(&xas);
474
475         expected_count += hpage_nr_pages(page) + page_has_private(page);
476         if (page_count(page) != expected_count || xas_load(&xas) != page) {
477                 xas_unlock_irq(&xas);
478                 return -EAGAIN;
479         }
480
481         if (!page_ref_freeze(page, expected_count)) {
482                 xas_unlock_irq(&xas);
483                 return -EAGAIN;
484         }
485
486         /*
487          * In the async migration case of moving a page with buffers, lock the
488          * buffers using trylock before the mapping is moved. If the mapping
489          * was moved, we later failed to lock the buffers and could not move
490          * the mapping back due to an elevated page count, we would have to
491          * block waiting on other references to be dropped.
492          */
493         if (mode == MIGRATE_ASYNC && head &&
494                         !buffer_migrate_lock_buffers(head, mode)) {
495                 page_ref_unfreeze(page, expected_count);
496                 xas_unlock_irq(&xas);
497                 return -EAGAIN;
498         }
499
500         /*
501          * Now we know that no one else is looking at the page:
502          * no turning back from here.
503          */
504         newpage->index = page->index;
505         newpage->mapping = page->mapping;
506         page_ref_add(newpage, hpage_nr_pages(page)); /* add cache reference */
507         if (PageSwapBacked(page)) {
508                 __SetPageSwapBacked(newpage);
509                 if (PageSwapCache(page)) {
510                         SetPageSwapCache(newpage);
511                         set_page_private(newpage, page_private(page));
512                 }
513         } else {
514                 VM_BUG_ON_PAGE(PageSwapCache(page), page);
515         }
516
517         /* Move dirty while page refs frozen and newpage not yet exposed */
518         dirty = PageDirty(page);
519         if (dirty) {
520                 ClearPageDirty(page);
521                 SetPageDirty(newpage);
522         }
523
524         xas_store(&xas, newpage);
525         if (PageTransHuge(page)) {
526                 int i;
527
528                 for (i = 1; i < HPAGE_PMD_NR; i++) {
529                         xas_next(&xas);
530                         xas_store(&xas, newpage + i);
531                 }
532         }
533
534         /*
535          * Drop cache reference from old page by unfreezing
536          * to one less reference.
537          * We know this isn't the last reference.
538          */
539         page_ref_unfreeze(page, expected_count - hpage_nr_pages(page));
540
541         xas_unlock(&xas);
542         /* Leave irq disabled to prevent preemption while updating stats */
543
544         /*
545          * If moved to a different zone then also account
546          * the page for that zone. Other VM counters will be
547          * taken care of when we establish references to the
548          * new page and drop references to the old page.
549          *
550          * Note that anonymous pages are accounted for
551          * via NR_FILE_PAGES and NR_ANON_MAPPED if they
552          * are mapped to swap space.
553          */
554         if (newzone != oldzone) {
555                 __dec_node_state(oldzone->zone_pgdat, NR_FILE_PAGES);
556                 __inc_node_state(newzone->zone_pgdat, NR_FILE_PAGES);
557                 if (PageSwapBacked(page) && !PageSwapCache(page)) {
558                         __dec_node_state(oldzone->zone_pgdat, NR_SHMEM);
559                         __inc_node_state(newzone->zone_pgdat, NR_SHMEM);
560                 }
561                 if (dirty && mapping_cap_account_dirty(mapping)) {
562                         __dec_node_state(oldzone->zone_pgdat, NR_FILE_DIRTY);
563                         __dec_zone_state(oldzone, NR_ZONE_WRITE_PENDING);
564                         __inc_node_state(newzone->zone_pgdat, NR_FILE_DIRTY);
565                         __inc_zone_state(newzone, NR_ZONE_WRITE_PENDING);
566                 }
567         }
568         local_irq_enable();
569
570         return MIGRATEPAGE_SUCCESS;
571 }
572 EXPORT_SYMBOL(migrate_page_move_mapping);
573
574 /*
575  * The expected number of remaining references is the same as that
576  * of migrate_page_move_mapping().
577  */
578 int migrate_huge_page_move_mapping(struct address_space *mapping,
579                                    struct page *newpage, struct page *page)
580 {
581         XA_STATE(xas, &mapping->i_pages, page_index(page));
582         int expected_count;
583
584         xas_lock_irq(&xas);
585         expected_count = 2 + page_has_private(page);
586         if (page_count(page) != expected_count || xas_load(&xas) != page) {
587                 xas_unlock_irq(&xas);
588                 return -EAGAIN;
589         }
590
591         if (!page_ref_freeze(page, expected_count)) {
592                 xas_unlock_irq(&xas);
593                 return -EAGAIN;
594         }
595
596         newpage->index = page->index;
597         newpage->mapping = page->mapping;
598
599         get_page(newpage);
600
601         xas_store(&xas, newpage);
602
603         page_ref_unfreeze(page, expected_count - 1);
604
605         xas_unlock_irq(&xas);
606
607         return MIGRATEPAGE_SUCCESS;
608 }
609
610 /*
611  * Gigantic pages are so large that we do not guarantee that page++ pointer
612  * arithmetic will work across the entire page.  We need something more
613  * specialized.
614  */
615 static void __copy_gigantic_page(struct page *dst, struct page *src,
616                                 int nr_pages)
617 {
618         int i;
619         struct page *dst_base = dst;
620         struct page *src_base = src;
621
622         for (i = 0; i < nr_pages; ) {
623                 cond_resched();
624                 copy_highpage(dst, src);
625
626                 i++;
627                 dst = mem_map_next(dst, dst_base, i);
628                 src = mem_map_next(src, src_base, i);
629         }
630 }
631
632 static void copy_huge_page(struct page *dst, struct page *src)
633 {
634         int i;
635         int nr_pages;
636
637         if (PageHuge(src)) {
638                 /* hugetlbfs page */
639                 struct hstate *h = page_hstate(src);
640                 nr_pages = pages_per_huge_page(h);
641
642                 if (unlikely(nr_pages > MAX_ORDER_NR_PAGES)) {
643                         __copy_gigantic_page(dst, src, nr_pages);
644                         return;
645                 }
646         } else {
647                 /* thp page */
648                 BUG_ON(!PageTransHuge(src));
649                 nr_pages = hpage_nr_pages(src);
650         }
651
652         for (i = 0; i < nr_pages; i++) {
653                 cond_resched();
654                 copy_highpage(dst + i, src + i);
655         }
656 }
657
658 /*
659  * Copy the page to its new location
660  */
661 void migrate_page_states(struct page *newpage, struct page *page)
662 {
663         int cpupid;
664
665         if (PageError(page))
666                 SetPageError(newpage);
667         if (PageReferenced(page))
668                 SetPageReferenced(newpage);
669         if (PageUptodate(page))
670                 SetPageUptodate(newpage);
671         if (TestClearPageActive(page)) {
672                 VM_BUG_ON_PAGE(PageUnevictable(page), page);
673                 SetPageActive(newpage);
674         } else if (TestClearPageUnevictable(page))
675                 SetPageUnevictable(newpage);
676         if (PageWorkingset(page))
677                 SetPageWorkingset(newpage);
678         if (PageChecked(page))
679                 SetPageChecked(newpage);
680         if (PageMappedToDisk(page))
681                 SetPageMappedToDisk(newpage);
682
683         /* Move dirty on pages not done by migrate_page_move_mapping() */
684         if (PageDirty(page))
685                 SetPageDirty(newpage);
686
687         if (page_is_young(page))
688                 set_page_young(newpage);
689         if (page_is_idle(page))
690                 set_page_idle(newpage);
691
692         /*
693          * Copy NUMA information to the new page, to prevent over-eager
694          * future migrations of this same page.
695          */
696         cpupid = page_cpupid_xchg_last(page, -1);
697         page_cpupid_xchg_last(newpage, cpupid);
698
699         ksm_migrate_page(newpage, page);
700         /*
701          * Please do not reorder this without considering how mm/ksm.c's
702          * get_ksm_page() depends upon ksm_migrate_page() and PageSwapCache().
703          */
704         if (PageSwapCache(page))
705                 ClearPageSwapCache(page);
706         ClearPagePrivate(page);
707         set_page_private(page, 0);
708
709         /*
710          * If any waiters have accumulated on the new page then
711          * wake them up.
712          */
713         if (PageWriteback(newpage))
714                 end_page_writeback(newpage);
715
716         copy_page_owner(page, newpage);
717
718         mem_cgroup_migrate(page, newpage);
719 }
720 EXPORT_SYMBOL(migrate_page_states);
721
722 void migrate_page_copy(struct page *newpage, struct page *page)
723 {
724         if (PageHuge(page) || PageTransHuge(page))
725                 copy_huge_page(newpage, page);
726         else
727                 copy_highpage(newpage, page);
728
729         migrate_page_states(newpage, page);
730 }
731 EXPORT_SYMBOL(migrate_page_copy);
732
733 /************************************************************
734  *                    Migration functions
735  ***********************************************************/
736
737 /*
738  * Common logic to directly migrate a single LRU page suitable for
739  * pages that do not use PagePrivate/PagePrivate2.
740  *
741  * Pages are locked upon entry and exit.
742  */
743 int migrate_page(struct address_space *mapping,
744                 struct page *newpage, struct page *page,
745                 enum migrate_mode mode)
746 {
747         int rc;
748
749         BUG_ON(PageWriteback(page));    /* Writeback must be complete */
750
751         rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0);
752
753         if (rc != MIGRATEPAGE_SUCCESS)
754                 return rc;
755
756         if (mode != MIGRATE_SYNC_NO_COPY)
757                 migrate_page_copy(newpage, page);
758         else
759                 migrate_page_states(newpage, page);
760         return MIGRATEPAGE_SUCCESS;
761 }
762 EXPORT_SYMBOL(migrate_page);
763
764 #ifdef CONFIG_BLOCK
765 /*
766  * Migration function for pages with buffers. This function can only be used
767  * if the underlying filesystem guarantees that no other references to "page"
768  * exist.
769  */
770 int buffer_migrate_page(struct address_space *mapping,
771                 struct page *newpage, struct page *page, enum migrate_mode mode)
772 {
773         struct buffer_head *bh, *head;
774         int rc;
775
776         if (!page_has_buffers(page))
777                 return migrate_page(mapping, newpage, page, mode);
778
779         head = page_buffers(page);
780
781         rc = migrate_page_move_mapping(mapping, newpage, page, head, mode, 0);
782
783         if (rc != MIGRATEPAGE_SUCCESS)
784                 return rc;
785
786         /*
787          * In the async case, migrate_page_move_mapping locked the buffers
788          * with an IRQ-safe spinlock held. In the sync case, the buffers
789          * need to be locked now
790          */
791         if (mode != MIGRATE_ASYNC)
792                 BUG_ON(!buffer_migrate_lock_buffers(head, mode));
793
794         ClearPagePrivate(page);
795         set_page_private(newpage, page_private(page));
796         set_page_private(page, 0);
797         put_page(page);
798         get_page(newpage);
799
800         bh = head;
801         do {
802                 set_bh_page(bh, newpage, bh_offset(bh));
803                 bh = bh->b_this_page;
804
805         } while (bh != head);
806
807         SetPagePrivate(newpage);
808
809         if (mode != MIGRATE_SYNC_NO_COPY)
810                 migrate_page_copy(newpage, page);
811         else
812                 migrate_page_states(newpage, page);
813
814         bh = head;
815         do {
816                 unlock_buffer(bh);
817                 put_bh(bh);
818                 bh = bh->b_this_page;
819
820         } while (bh != head);
821
822         return MIGRATEPAGE_SUCCESS;
823 }
824 EXPORT_SYMBOL(buffer_migrate_page);
825 #endif
826
827 /*
828  * Writeback a page to clean the dirty state
829  */
830 static int writeout(struct address_space *mapping, struct page *page)
831 {
832         struct writeback_control wbc = {
833                 .sync_mode = WB_SYNC_NONE,
834                 .nr_to_write = 1,
835                 .range_start = 0,
836                 .range_end = LLONG_MAX,
837                 .for_reclaim = 1
838         };
839         int rc;
840
841         if (!mapping->a_ops->writepage)
842                 /* No write method for the address space */
843                 return -EINVAL;
844
845         if (!clear_page_dirty_for_io(page))
846                 /* Someone else already triggered a write */
847                 return -EAGAIN;
848
849         /*
850          * A dirty page may imply that the underlying filesystem has
851          * the page on some queue. So the page must be clean for
852          * migration. Writeout may mean we loose the lock and the
853          * page state is no longer what we checked for earlier.
854          * At this point we know that the migration attempt cannot
855          * be successful.
856          */
857         remove_migration_ptes(page, page, false);
858
859         rc = mapping->a_ops->writepage(page, &wbc);
860
861         if (rc != AOP_WRITEPAGE_ACTIVATE)
862                 /* unlocked. Relock */
863                 lock_page(page);
864
865         return (rc < 0) ? -EIO : -EAGAIN;
866 }
867
868 /*
869  * Default handling if a filesystem does not provide a migration function.
870  */
871 static int fallback_migrate_page(struct address_space *mapping,
872         struct page *newpage, struct page *page, enum migrate_mode mode)
873 {
874         if (PageDirty(page)) {
875                 /* Only writeback pages in full synchronous migration */
876                 switch (mode) {
877                 case MIGRATE_SYNC:
878                 case MIGRATE_SYNC_NO_COPY:
879                         break;
880                 default:
881                         return -EBUSY;
882                 }
883                 return writeout(mapping, page);
884         }
885
886         /*
887          * Buffers may be managed in a filesystem specific way.
888          * We must have no buffers or drop them.
889          */
890         if (page_has_private(page) &&
891             !try_to_release_page(page, GFP_KERNEL))
892                 return -EAGAIN;
893
894         return migrate_page(mapping, newpage, page, mode);
895 }
896
897 /*
898  * Move a page to a newly allocated page
899  * The page is locked and all ptes have been successfully removed.
900  *
901  * The new page will have replaced the old page if this function
902  * is successful.
903  *
904  * Return value:
905  *   < 0 - error code
906  *  MIGRATEPAGE_SUCCESS - success
907  */
908 static int move_to_new_page(struct page *newpage, struct page *page,
909                                 enum migrate_mode mode)
910 {
911         struct address_space *mapping;
912         int rc = -EAGAIN;
913         bool is_lru = !__PageMovable(page);
914
915         VM_BUG_ON_PAGE(!PageLocked(page), page);
916         VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
917
918         mapping = page_mapping(page);
919
920         if (likely(is_lru)) {
921                 if (!mapping)
922                         rc = migrate_page(mapping, newpage, page, mode);
923                 else if (mapping->a_ops->migratepage)
924                         /*
925                          * Most pages have a mapping and most filesystems
926                          * provide a migratepage callback. Anonymous pages
927                          * are part of swap space which also has its own
928                          * migratepage callback. This is the most common path
929                          * for page migration.
930                          */
931                         rc = mapping->a_ops->migratepage(mapping, newpage,
932                                                         page, mode);
933                 else
934                         rc = fallback_migrate_page(mapping, newpage,
935                                                         page, mode);
936         } else {
937                 /*
938                  * In case of non-lru page, it could be released after
939                  * isolation step. In that case, we shouldn't try migration.
940                  */
941                 VM_BUG_ON_PAGE(!PageIsolated(page), page);
942                 if (!PageMovable(page)) {
943                         rc = MIGRATEPAGE_SUCCESS;
944                         __ClearPageIsolated(page);
945                         goto out;
946                 }
947
948                 rc = mapping->a_ops->migratepage(mapping, newpage,
949                                                 page, mode);
950                 WARN_ON_ONCE(rc == MIGRATEPAGE_SUCCESS &&
951                         !PageIsolated(page));
952         }
953
954         /*
955          * When successful, old pagecache page->mapping must be cleared before
956          * page is freed; but stats require that PageAnon be left as PageAnon.
957          */
958         if (rc == MIGRATEPAGE_SUCCESS) {
959                 if (__PageMovable(page)) {
960                         VM_BUG_ON_PAGE(!PageIsolated(page), page);
961
962                         /*
963                          * We clear PG_movable under page_lock so any compactor
964                          * cannot try to migrate this page.
965                          */
966                         __ClearPageIsolated(page);
967                 }
968
969                 /*
970                  * Anonymous and movable page->mapping will be cleard by
971                  * free_pages_prepare so don't reset it here for keeping
972                  * the type to work PageAnon, for example.
973                  */
974                 if (!PageMappingFlags(page))
975                         page->mapping = NULL;
976         }
977 out:
978         return rc;
979 }
980
981 static int __unmap_and_move(struct page *page, struct page *newpage,
982                                 int force, enum migrate_mode mode)
983 {
984         int rc = -EAGAIN;
985         int page_was_mapped = 0;
986         struct anon_vma *anon_vma = NULL;
987         bool is_lru = !__PageMovable(page);
988
989         if (!trylock_page(page)) {
990                 if (!force || mode == MIGRATE_ASYNC)
991                         goto out;
992
993                 /*
994                  * It's not safe for direct compaction to call lock_page.
995                  * For example, during page readahead pages are added locked
996                  * to the LRU. Later, when the IO completes the pages are
997                  * marked uptodate and unlocked. However, the queueing
998                  * could be merging multiple pages for one bio (e.g.
999                  * mpage_readpages). If an allocation happens for the
1000                  * second or third page, the process can end up locking
1001                  * the same page twice and deadlocking. Rather than
1002                  * trying to be clever about what pages can be locked,
1003                  * avoid the use of lock_page for direct compaction
1004                  * altogether.
1005                  */
1006                 if (current->flags & PF_MEMALLOC)
1007                         goto out;
1008
1009                 lock_page(page);
1010         }
1011
1012         if (PageWriteback(page)) {
1013                 /*
1014                  * Only in the case of a full synchronous migration is it
1015                  * necessary to wait for PageWriteback. In the async case,
1016                  * the retry loop is too short and in the sync-light case,
1017                  * the overhead of stalling is too much
1018                  */
1019                 switch (mode) {
1020                 case MIGRATE_SYNC:
1021                 case MIGRATE_SYNC_NO_COPY:
1022                         break;
1023                 default:
1024                         rc = -EBUSY;
1025                         goto out_unlock;
1026                 }
1027                 if (!force)
1028                         goto out_unlock;
1029                 wait_on_page_writeback(page);
1030         }
1031
1032         /*
1033          * By try_to_unmap(), page->mapcount goes down to 0 here. In this case,
1034          * we cannot notice that anon_vma is freed while we migrates a page.
1035          * This get_anon_vma() delays freeing anon_vma pointer until the end
1036          * of migration. File cache pages are no problem because of page_lock()
1037          * File Caches may use write_page() or lock_page() in migration, then,
1038          * just care Anon page here.
1039          *
1040          * Only page_get_anon_vma() understands the subtleties of
1041          * getting a hold on an anon_vma from outside one of its mms.
1042          * But if we cannot get anon_vma, then we won't need it anyway,
1043          * because that implies that the anon page is no longer mapped
1044          * (and cannot be remapped so long as we hold the page lock).
1045          */
1046         if (PageAnon(page) && !PageKsm(page))
1047                 anon_vma = page_get_anon_vma(page);
1048
1049         /*
1050          * Block others from accessing the new page when we get around to
1051          * establishing additional references. We are usually the only one
1052          * holding a reference to newpage at this point. We used to have a BUG
1053          * here if trylock_page(newpage) fails, but would like to allow for
1054          * cases where there might be a race with the previous use of newpage.
1055          * This is much like races on refcount of oldpage: just don't BUG().
1056          */
1057         if (unlikely(!trylock_page(newpage)))
1058                 goto out_unlock;
1059
1060         if (unlikely(!is_lru)) {
1061                 rc = move_to_new_page(newpage, page, mode);
1062                 goto out_unlock_both;
1063         }
1064
1065         /*
1066          * Corner case handling:
1067          * 1. When a new swap-cache page is read into, it is added to the LRU
1068          * and treated as swapcache but it has no rmap yet.
1069          * Calling try_to_unmap() against a page->mapping==NULL page will
1070          * trigger a BUG.  So handle it here.
1071          * 2. An orphaned page (see truncate_complete_page) might have
1072          * fs-private metadata. The page can be picked up due to memory
1073          * offlining.  Everywhere else except page reclaim, the page is
1074          * invisible to the vm, so the page can not be migrated.  So try to
1075          * free the metadata, so the page can be freed.
1076          */
1077         if (!page->mapping) {
1078                 VM_BUG_ON_PAGE(PageAnon(page), page);
1079                 if (page_has_private(page)) {
1080                         try_to_free_buffers(page);
1081                         goto out_unlock_both;
1082                 }
1083         } else if (page_mapped(page)) {
1084                 /* Establish migration ptes */
1085                 VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
1086                                 page);
1087                 try_to_unmap(page,
1088                         TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1089                 page_was_mapped = 1;
1090         }
1091
1092         if (!page_mapped(page))
1093                 rc = move_to_new_page(newpage, page, mode);
1094
1095         if (page_was_mapped)
1096                 remove_migration_ptes(page,
1097                         rc == MIGRATEPAGE_SUCCESS ? newpage : page, false);
1098
1099 out_unlock_both:
1100         unlock_page(newpage);
1101 out_unlock:
1102         /* Drop an anon_vma reference if we took one */
1103         if (anon_vma)
1104                 put_anon_vma(anon_vma);
1105         unlock_page(page);
1106 out:
1107         /*
1108          * If migration is successful, decrease refcount of the newpage
1109          * which will not free the page because new page owner increased
1110          * refcounter. As well, if it is LRU page, add the page to LRU
1111          * list in here.
1112          */
1113         if (rc == MIGRATEPAGE_SUCCESS) {
1114                 if (unlikely(__PageMovable(newpage)))
1115                         put_page(newpage);
1116                 else
1117                         putback_lru_page(newpage);
1118         }
1119
1120         return rc;
1121 }
1122
1123 /*
1124  * gcc 4.7 and 4.8 on arm get an ICEs when inlining unmap_and_move().  Work
1125  * around it.
1126  */
1127 #if defined(CONFIG_ARM) && \
1128         defined(GCC_VERSION) && GCC_VERSION < 40900 && GCC_VERSION >= 40700
1129 #define ICE_noinline noinline
1130 #else
1131 #define ICE_noinline
1132 #endif
1133
1134 /*
1135  * Obtain the lock on page, remove all ptes and migrate the page
1136  * to the newly allocated page in newpage.
1137  */
1138 static ICE_noinline int unmap_and_move(new_page_t get_new_page,
1139                                    free_page_t put_new_page,
1140                                    unsigned long private, struct page *page,
1141                                    int force, enum migrate_mode mode,
1142                                    enum migrate_reason reason)
1143 {
1144         int rc = MIGRATEPAGE_SUCCESS;
1145         struct page *newpage;
1146
1147         if (!thp_migration_supported() && PageTransHuge(page))
1148                 return -ENOMEM;
1149
1150         newpage = get_new_page(page, private);
1151         if (!newpage)
1152                 return -ENOMEM;
1153
1154         if (page_count(page) == 1) {
1155                 /* page was freed from under us. So we are done. */
1156                 ClearPageActive(page);
1157                 ClearPageUnevictable(page);
1158                 if (unlikely(__PageMovable(page))) {
1159                         lock_page(page);
1160                         if (!PageMovable(page))
1161                                 __ClearPageIsolated(page);
1162                         unlock_page(page);
1163                 }
1164                 if (put_new_page)
1165                         put_new_page(newpage, private);
1166                 else
1167                         put_page(newpage);
1168                 goto out;
1169         }
1170
1171         rc = __unmap_and_move(page, newpage, force, mode);
1172         if (rc == MIGRATEPAGE_SUCCESS)
1173                 set_page_owner_migrate_reason(newpage, reason);
1174
1175 out:
1176         if (rc != -EAGAIN) {
1177                 /*
1178                  * A page that has been migrated has all references
1179                  * removed and will be freed. A page that has not been
1180                  * migrated will have kepts its references and be
1181                  * restored.
1182                  */
1183                 list_del(&page->lru);
1184
1185                 /*
1186                  * Compaction can migrate also non-LRU pages which are
1187                  * not accounted to NR_ISOLATED_*. They can be recognized
1188                  * as __PageMovable
1189                  */
1190                 if (likely(!__PageMovable(page)))
1191                         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON +
1192                                         page_is_file_cache(page), -hpage_nr_pages(page));
1193         }
1194
1195         /*
1196          * If migration is successful, releases reference grabbed during
1197          * isolation. Otherwise, restore the page to right list unless
1198          * we want to retry.
1199          */
1200         if (rc == MIGRATEPAGE_SUCCESS) {
1201                 put_page(page);
1202                 if (reason == MR_MEMORY_FAILURE) {
1203                         /*
1204                          * Set PG_HWPoison on just freed page
1205                          * intentionally. Although it's rather weird,
1206                          * it's how HWPoison flag works at the moment.
1207                          */
1208                         if (set_hwpoison_free_buddy_page(page))
1209                                 num_poisoned_pages_inc();
1210                 }
1211         } else {
1212                 if (rc != -EAGAIN) {
1213                         if (likely(!__PageMovable(page))) {
1214                                 putback_lru_page(page);
1215                                 goto put_new;
1216                         }
1217
1218                         lock_page(page);
1219                         if (PageMovable(page))
1220                                 putback_movable_page(page);
1221                         else
1222                                 __ClearPageIsolated(page);
1223                         unlock_page(page);
1224                         put_page(page);
1225                 }
1226 put_new:
1227                 if (put_new_page)
1228                         put_new_page(newpage, private);
1229                 else
1230                         put_page(newpage);
1231         }
1232
1233         return rc;
1234 }
1235
1236 /*
1237  * Counterpart of unmap_and_move_page() for hugepage migration.
1238  *
1239  * This function doesn't wait the completion of hugepage I/O
1240  * because there is no race between I/O and migration for hugepage.
1241  * Note that currently hugepage I/O occurs only in direct I/O
1242  * where no lock is held and PG_writeback is irrelevant,
1243  * and writeback status of all subpages are counted in the reference
1244  * count of the head page (i.e. if all subpages of a 2MB hugepage are
1245  * under direct I/O, the reference of the head page is 512 and a bit more.)
1246  * This means that when we try to migrate hugepage whose subpages are
1247  * doing direct I/O, some references remain after try_to_unmap() and
1248  * hugepage migration fails without data corruption.
1249  *
1250  * There is also no race when direct I/O is issued on the page under migration,
1251  * because then pte is replaced with migration swap entry and direct I/O code
1252  * will wait in the page fault for migration to complete.
1253  */
1254 static int unmap_and_move_huge_page(new_page_t get_new_page,
1255                                 free_page_t put_new_page, unsigned long private,
1256                                 struct page *hpage, int force,
1257                                 enum migrate_mode mode, int reason)
1258 {
1259         int rc = -EAGAIN;
1260         int page_was_mapped = 0;
1261         struct page *new_hpage;
1262         struct anon_vma *anon_vma = NULL;
1263
1264         /*
1265          * Movability of hugepages depends on architectures and hugepage size.
1266          * This check is necessary because some callers of hugepage migration
1267          * like soft offline and memory hotremove don't walk through page
1268          * tables or check whether the hugepage is pmd-based or not before
1269          * kicking migration.
1270          */
1271         if (!hugepage_migration_supported(page_hstate(hpage))) {
1272                 putback_active_hugepage(hpage);
1273                 return -ENOSYS;
1274         }
1275
1276         new_hpage = get_new_page(hpage, private);
1277         if (!new_hpage)
1278                 return -ENOMEM;
1279
1280         if (!trylock_page(hpage)) {
1281                 if (!force)
1282                         goto out;
1283                 switch (mode) {
1284                 case MIGRATE_SYNC:
1285                 case MIGRATE_SYNC_NO_COPY:
1286                         break;
1287                 default:
1288                         goto out;
1289                 }
1290                 lock_page(hpage);
1291         }
1292
1293         if (PageAnon(hpage))
1294                 anon_vma = page_get_anon_vma(hpage);
1295
1296         if (unlikely(!trylock_page(new_hpage)))
1297                 goto put_anon;
1298
1299         if (page_mapped(hpage)) {
1300                 try_to_unmap(hpage,
1301                         TTU_MIGRATION|TTU_IGNORE_MLOCK|TTU_IGNORE_ACCESS);
1302                 page_was_mapped = 1;
1303         }
1304
1305         if (!page_mapped(hpage))
1306                 rc = move_to_new_page(new_hpage, hpage, mode);
1307
1308         if (page_was_mapped)
1309                 remove_migration_ptes(hpage,
1310                         rc == MIGRATEPAGE_SUCCESS ? new_hpage : hpage, false);
1311
1312         unlock_page(new_hpage);
1313
1314 put_anon:
1315         if (anon_vma)
1316                 put_anon_vma(anon_vma);
1317
1318         if (rc == MIGRATEPAGE_SUCCESS) {
1319                 move_hugetlb_state(hpage, new_hpage, reason);
1320                 put_new_page = NULL;
1321         }
1322
1323         unlock_page(hpage);
1324 out:
1325         if (rc != -EAGAIN)
1326                 putback_active_hugepage(hpage);
1327
1328         /*
1329          * If migration was not successful and there's a freeing callback, use
1330          * it.  Otherwise, put_page() will drop the reference grabbed during
1331          * isolation.
1332          */
1333         if (put_new_page)
1334                 put_new_page(new_hpage, private);
1335         else
1336                 putback_active_hugepage(new_hpage);
1337
1338         return rc;
1339 }
1340
1341 /*
1342  * migrate_pages - migrate the pages specified in a list, to the free pages
1343  *                 supplied as the target for the page migration
1344  *
1345  * @from:               The list of pages to be migrated.
1346  * @get_new_page:       The function used to allocate free pages to be used
1347  *                      as the target of the page migration.
1348  * @put_new_page:       The function used to free target pages if migration
1349  *                      fails, or NULL if no special handling is necessary.
1350  * @private:            Private data to be passed on to get_new_page()
1351  * @mode:               The migration mode that specifies the constraints for
1352  *                      page migration, if any.
1353  * @reason:             The reason for page migration.
1354  *
1355  * The function returns after 10 attempts or if no pages are movable any more
1356  * because the list has become empty or no retryable pages exist any more.
1357  * The caller should call putback_movable_pages() to return pages to the LRU
1358  * or free list only if ret != 0.
1359  *
1360  * Returns the number of pages that were not migrated, or an error code.
1361  */
1362 int migrate_pages(struct list_head *from, new_page_t get_new_page,
1363                 free_page_t put_new_page, unsigned long private,
1364                 enum migrate_mode mode, int reason)
1365 {
1366         int retry = 1;
1367         int nr_failed = 0;
1368         int nr_succeeded = 0;
1369         int pass = 0;
1370         struct page *page;
1371         struct page *page2;
1372         int swapwrite = current->flags & PF_SWAPWRITE;
1373         int rc;
1374
1375         if (!swapwrite)
1376                 current->flags |= PF_SWAPWRITE;
1377
1378         for(pass = 0; pass < 10 && retry; pass++) {
1379                 retry = 0;
1380
1381                 list_for_each_entry_safe(page, page2, from, lru) {
1382 retry:
1383                         cond_resched();
1384
1385                         if (PageHuge(page))
1386                                 rc = unmap_and_move_huge_page(get_new_page,
1387                                                 put_new_page, private, page,
1388                                                 pass > 2, mode, reason);
1389                         else
1390                                 rc = unmap_and_move(get_new_page, put_new_page,
1391                                                 private, page, pass > 2, mode,
1392                                                 reason);
1393
1394                         switch(rc) {
1395                         case -ENOMEM:
1396                                 /*
1397                                  * THP migration might be unsupported or the
1398                                  * allocation could've failed so we should
1399                                  * retry on the same page with the THP split
1400                                  * to base pages.
1401                                  *
1402                                  * Head page is retried immediately and tail
1403                                  * pages are added to the tail of the list so
1404                                  * we encounter them after the rest of the list
1405                                  * is processed.
1406                                  */
1407                                 if (PageTransHuge(page) && !PageHuge(page)) {
1408                                         lock_page(page);
1409                                         rc = split_huge_page_to_list(page, from);
1410                                         unlock_page(page);
1411                                         if (!rc) {
1412                                                 list_safe_reset_next(page, page2, lru);
1413                                                 goto retry;
1414                                         }
1415                                 }
1416                                 nr_failed++;
1417                                 goto out;
1418                         case -EAGAIN:
1419                                 retry++;
1420                                 break;
1421                         case MIGRATEPAGE_SUCCESS:
1422                                 nr_succeeded++;
1423                                 break;
1424                         default:
1425                                 /*
1426                                  * Permanent failure (-EBUSY, -ENOSYS, etc.):
1427                                  * unlike -EAGAIN case, the failed page is
1428                                  * removed from migration page list and not
1429                                  * retried in the next outer loop.
1430                                  */
1431                                 nr_failed++;
1432                                 break;
1433                         }
1434                 }
1435         }
1436         nr_failed += retry;
1437         rc = nr_failed;
1438 out:
1439         if (nr_succeeded)
1440                 count_vm_events(PGMIGRATE_SUCCESS, nr_succeeded);
1441         if (nr_failed)
1442                 count_vm_events(PGMIGRATE_FAIL, nr_failed);
1443         trace_mm_migrate_pages(nr_succeeded, nr_failed, mode, reason);
1444
1445         if (!swapwrite)
1446                 current->flags &= ~PF_SWAPWRITE;
1447
1448         return rc;
1449 }
1450
1451 #ifdef CONFIG_NUMA
1452
1453 static int store_status(int __user *status, int start, int value, int nr)
1454 {
1455         while (nr-- > 0) {
1456                 if (put_user(value, status + start))
1457                         return -EFAULT;
1458                 start++;
1459         }
1460
1461         return 0;
1462 }
1463
1464 static int do_move_pages_to_node(struct mm_struct *mm,
1465                 struct list_head *pagelist, int node)
1466 {
1467         int err;
1468
1469         if (list_empty(pagelist))
1470                 return 0;
1471
1472         err = migrate_pages(pagelist, alloc_new_node_page, NULL, node,
1473                         MIGRATE_SYNC, MR_SYSCALL);
1474         if (err)
1475                 putback_movable_pages(pagelist);
1476         return err;
1477 }
1478
1479 /*
1480  * Resolves the given address to a struct page, isolates it from the LRU and
1481  * puts it to the given pagelist.
1482  * Returns -errno if the page cannot be found/isolated or 0 when it has been
1483  * queued or the page doesn't need to be migrated because it is already on
1484  * the target node
1485  */
1486 static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
1487                 int node, struct list_head *pagelist, bool migrate_all)
1488 {
1489         struct vm_area_struct *vma;
1490         struct page *page;
1491         unsigned int follflags;
1492         int err;
1493
1494         down_read(&mm->mmap_sem);
1495         err = -EFAULT;
1496         vma = find_vma(mm, addr);
1497         if (!vma || addr < vma->vm_start || !vma_migratable(vma))
1498                 goto out;
1499
1500         /* FOLL_DUMP to ignore special (like zero) pages */
1501         follflags = FOLL_GET | FOLL_DUMP;
1502         page = follow_page(vma, addr, follflags);
1503
1504         err = PTR_ERR(page);
1505         if (IS_ERR(page))
1506                 goto out;
1507
1508         err = -ENOENT;
1509         if (!page)
1510                 goto out;
1511
1512         err = 0;
1513         if (page_to_nid(page) == node)
1514                 goto out_putpage;
1515
1516         err = -EACCES;
1517         if (page_mapcount(page) > 1 && !migrate_all)
1518                 goto out_putpage;
1519
1520         if (PageHuge(page)) {
1521                 if (PageHead(page)) {
1522                         isolate_huge_page(page, pagelist);
1523                         err = 0;
1524                 }
1525         } else {
1526                 struct page *head;
1527
1528                 head = compound_head(page);
1529                 err = isolate_lru_page(head);
1530                 if (err)
1531                         goto out_putpage;
1532
1533                 err = 0;
1534                 list_add_tail(&head->lru, pagelist);
1535                 mod_node_page_state(page_pgdat(head),
1536                         NR_ISOLATED_ANON + page_is_file_cache(head),
1537                         hpage_nr_pages(head));
1538         }
1539 out_putpage:
1540         /*
1541          * Either remove the duplicate refcount from
1542          * isolate_lru_page() or drop the page ref if it was
1543          * not isolated.
1544          */
1545         put_page(page);
1546 out:
1547         up_read(&mm->mmap_sem);
1548         return err;
1549 }
1550
1551 /*
1552  * Migrate an array of page address onto an array of nodes and fill
1553  * the corresponding array of status.
1554  */
1555 static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
1556                          unsigned long nr_pages,
1557                          const void __user * __user *pages,
1558                          const int __user *nodes,
1559                          int __user *status, int flags)
1560 {
1561         int current_node = NUMA_NO_NODE;
1562         LIST_HEAD(pagelist);
1563         int start, i;
1564         int err = 0, err1;
1565
1566         migrate_prep();
1567
1568         for (i = start = 0; i < nr_pages; i++) {
1569                 const void __user *p;
1570                 unsigned long addr;
1571                 int node;
1572
1573                 err = -EFAULT;
1574                 if (get_user(p, pages + i))
1575                         goto out_flush;
1576                 if (get_user(node, nodes + i))
1577                         goto out_flush;
1578                 addr = (unsigned long)p;
1579
1580                 err = -ENODEV;
1581                 if (node < 0 || node >= MAX_NUMNODES)
1582                         goto out_flush;
1583                 if (!node_state(node, N_MEMORY))
1584                         goto out_flush;
1585
1586                 err = -EACCES;
1587                 if (!node_isset(node, task_nodes))
1588                         goto out_flush;
1589
1590                 if (current_node == NUMA_NO_NODE) {
1591                         current_node = node;
1592                         start = i;
1593                 } else if (node != current_node) {
1594                         err = do_move_pages_to_node(mm, &pagelist, current_node);
1595                         if (err)
1596                                 goto out;
1597                         err = store_status(status, start, current_node, i - start);
1598                         if (err)
1599                                 goto out;
1600                         start = i;
1601                         current_node = node;
1602                 }
1603
1604                 /*
1605                  * Errors in the page lookup or isolation are not fatal and we simply
1606                  * report them via status
1607                  */
1608                 err = add_page_for_migration(mm, addr, current_node,
1609                                 &pagelist, flags & MPOL_MF_MOVE_ALL);
1610                 if (!err)
1611                         continue;
1612
1613                 err = store_status(status, i, err, 1);
1614                 if (err)
1615                         goto out_flush;
1616
1617                 err = do_move_pages_to_node(mm, &pagelist, current_node);
1618                 if (err)
1619                         goto out;
1620                 if (i > start) {
1621                         err = store_status(status, start, current_node, i - start);
1622                         if (err)
1623                                 goto out;
1624                 }
1625                 current_node = NUMA_NO_NODE;
1626         }
1627 out_flush:
1628         if (list_empty(&pagelist))
1629                 return err;
1630
1631         /* Make sure we do not overwrite the existing error */
1632         err1 = do_move_pages_to_node(mm, &pagelist, current_node);
1633         if (!err1)
1634                 err1 = store_status(status, start, current_node, i - start);
1635         if (!err)
1636                 err = err1;
1637 out:
1638         return err;
1639 }
1640
1641 /*
1642  * Determine the nodes of an array of pages and store it in an array of status.
1643  */
1644 static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages,
1645                                 const void __user **pages, int *status)
1646 {
1647         unsigned long i;
1648
1649         down_read(&mm->mmap_sem);
1650
1651         for (i = 0; i < nr_pages; i++) {
1652                 unsigned long addr = (unsigned long)(*pages);
1653                 struct vm_area_struct *vma;
1654                 struct page *page;
1655                 int err = -EFAULT;
1656
1657                 vma = find_vma(mm, addr);
1658                 if (!vma || addr < vma->vm_start)
1659                         goto set_status;
1660
1661                 /* FOLL_DUMP to ignore special (like zero) pages */
1662                 page = follow_page(vma, addr, FOLL_DUMP);
1663
1664                 err = PTR_ERR(page);
1665                 if (IS_ERR(page))
1666                         goto set_status;
1667
1668                 err = page ? page_to_nid(page) : -ENOENT;
1669 set_status:
1670                 *status = err;
1671
1672                 pages++;
1673                 status++;
1674         }
1675
1676         up_read(&mm->mmap_sem);
1677 }
1678
1679 /*
1680  * Determine the nodes of a user array of pages and store it in
1681  * a user array of status.
1682  */
1683 static int do_pages_stat(struct mm_struct *mm, unsigned long nr_pages,
1684                          const void __user * __user *pages,
1685                          int __user *status)
1686 {
1687 #define DO_PAGES_STAT_CHUNK_NR 16
1688         const void __user *chunk_pages[DO_PAGES_STAT_CHUNK_NR];
1689         int chunk_status[DO_PAGES_STAT_CHUNK_NR];
1690
1691         while (nr_pages) {
1692                 unsigned long chunk_nr;
1693
1694                 chunk_nr = nr_pages;
1695                 if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
1696                         chunk_nr = DO_PAGES_STAT_CHUNK_NR;
1697
1698                 if (copy_from_user(chunk_pages, pages, chunk_nr * sizeof(*chunk_pages)))
1699                         break;
1700
1701                 do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);
1702
1703                 if (copy_to_user(status, chunk_status, chunk_nr * sizeof(*status)))
1704                         break;
1705
1706                 pages += chunk_nr;
1707                 status += chunk_nr;
1708                 nr_pages -= chunk_nr;
1709         }
1710         return nr_pages ? -EFAULT : 0;
1711 }
1712
1713 /*
1714  * Move a list of pages in the address space of the currently executing
1715  * process.
1716  */
1717 static int kernel_move_pages(pid_t pid, unsigned long nr_pages,
1718                              const void __user * __user *pages,
1719                              const int __user *nodes,
1720                              int __user *status, int flags)
1721 {
1722         struct task_struct *task;
1723         struct mm_struct *mm;
1724         int err;
1725         nodemask_t task_nodes;
1726
1727         /* Check flags */
1728         if (flags & ~(MPOL_MF_MOVE|MPOL_MF_MOVE_ALL))
1729                 return -EINVAL;
1730
1731         if ((flags & MPOL_MF_MOVE_ALL) && !capable(CAP_SYS_NICE))
1732                 return -EPERM;
1733
1734         /* Find the mm_struct */
1735         rcu_read_lock();
1736         task = pid ? find_task_by_vpid(pid) : current;
1737         if (!task) {
1738                 rcu_read_unlock();
1739                 return -ESRCH;
1740         }
1741         get_task_struct(task);
1742
1743         /*
1744          * Check if this process has the right to modify the specified
1745          * process. Use the regular "ptrace_may_access()" checks.
1746          */
1747         if (!ptrace_may_access(task, PTRACE_MODE_READ_REALCREDS)) {
1748                 rcu_read_unlock();
1749                 err = -EPERM;
1750                 goto out;
1751         }
1752         rcu_read_unlock();
1753
1754         err = security_task_movememory(task);
1755         if (err)
1756                 goto out;
1757
1758         task_nodes = cpuset_mems_allowed(task);
1759         mm = get_task_mm(task);
1760         put_task_struct(task);
1761
1762         if (!mm)
1763                 return -EINVAL;
1764
1765         if (nodes)
1766                 err = do_pages_move(mm, task_nodes, nr_pages, pages,
1767                                     nodes, status, flags);
1768         else
1769                 err = do_pages_stat(mm, nr_pages, pages, status);
1770
1771         mmput(mm);
1772         return err;
1773
1774 out:
1775         put_task_struct(task);
1776         return err;
1777 }
1778
1779 SYSCALL_DEFINE6(move_pages, pid_t, pid, unsigned long, nr_pages,
1780                 const void __user * __user *, pages,
1781                 const int __user *, nodes,
1782                 int __user *, status, int, flags)
1783 {
1784         return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
1785 }
1786
1787 #ifdef CONFIG_COMPAT
1788 COMPAT_SYSCALL_DEFINE6(move_pages, pid_t, pid, compat_ulong_t, nr_pages,
1789                        compat_uptr_t __user *, pages32,
1790                        const int __user *, nodes,
1791                        int __user *, status,
1792                        int, flags)
1793 {
1794         const void __user * __user *pages;
1795         int i;
1796
1797         pages = compat_alloc_user_space(nr_pages * sizeof(void *));
1798         for (i = 0; i < nr_pages; i++) {
1799                 compat_uptr_t p;
1800
1801                 if (get_user(p, pages32 + i) ||
1802                         put_user(compat_ptr(p), pages + i))
1803                         return -EFAULT;
1804         }
1805         return kernel_move_pages(pid, nr_pages, pages, nodes, status, flags);
1806 }
1807 #endif /* CONFIG_COMPAT */
1808
1809 #ifdef CONFIG_NUMA_BALANCING
1810 /*
1811  * Returns true if this is a safe migration target node for misplaced NUMA
1812  * pages. Currently it only checks the watermarks which crude
1813  */
1814 static bool migrate_balanced_pgdat(struct pglist_data *pgdat,
1815                                    unsigned long nr_migrate_pages)
1816 {
1817         int z;
1818
1819         for (z = pgdat->nr_zones - 1; z >= 0; z--) {
1820                 struct zone *zone = pgdat->node_zones + z;
1821
1822                 if (!populated_zone(zone))
1823                         continue;
1824
1825                 /* Avoid waking kswapd by allocating pages_to_migrate pages. */
1826                 if (!zone_watermark_ok(zone, 0,
1827                                        high_wmark_pages(zone) +
1828                                        nr_migrate_pages,
1829                                        0, 0))
1830                         continue;
1831                 return true;
1832         }
1833         return false;
1834 }
1835
1836 static struct page *alloc_misplaced_dst_page(struct page *page,
1837                                            unsigned long data)
1838 {
1839         int nid = (int) data;
1840         struct page *newpage;
1841
1842         newpage = __alloc_pages_node(nid,
1843                                          (GFP_HIGHUSER_MOVABLE |
1844                                           __GFP_THISNODE | __GFP_NOMEMALLOC |
1845                                           __GFP_NORETRY | __GFP_NOWARN) &
1846                                          ~__GFP_RECLAIM, 0);
1847
1848         return newpage;
1849 }
1850
1851 static int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
1852 {
1853         int page_lru;
1854
1855         VM_BUG_ON_PAGE(compound_order(page) && !PageTransHuge(page), page);
1856
1857         /* Avoid migrating to a node that is nearly full */
1858         if (!migrate_balanced_pgdat(pgdat, 1UL << compound_order(page)))
1859                 return 0;
1860
1861         if (isolate_lru_page(page))
1862                 return 0;
1863
1864         /*
1865          * migrate_misplaced_transhuge_page() skips page migration's usual
1866          * check on page_count(), so we must do it here, now that the page
1867          * has been isolated: a GUP pin, or any other pin, prevents migration.
1868          * The expected page count is 3: 1 for page's mapcount and 1 for the
1869          * caller's pin and 1 for the reference taken by isolate_lru_page().
1870          */
1871         if (PageTransHuge(page) && page_count(page) != 3) {
1872                 putback_lru_page(page);
1873                 return 0;
1874         }
1875
1876         page_lru = page_is_file_cache(page);
1877         mod_node_page_state(page_pgdat(page), NR_ISOLATED_ANON + page_lru,
1878                                 hpage_nr_pages(page));
1879
1880         /*
1881          * Isolating the page has taken another reference, so the
1882          * caller's reference can be safely dropped without the page
1883          * disappearing underneath us during migration.
1884          */
1885         put_page(page);
1886         return 1;
1887 }
1888
1889 bool pmd_trans_migrating(pmd_t pmd)
1890 {
1891         struct page *page = pmd_page(pmd);
1892         return PageLocked(page);
1893 }
1894
1895 /*
1896  * Attempt to migrate a misplaced page to the specified destination
1897  * node. Caller is expected to have an elevated reference count on
1898  * the page that will be dropped by this function before returning.
1899  */
1900 int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
1901                            int node)
1902 {
1903         pg_data_t *pgdat = NODE_DATA(node);
1904         int isolated;
1905         int nr_remaining;
1906         LIST_HEAD(migratepages);
1907
1908         /*
1909          * Don't migrate file pages that are mapped in multiple processes
1910          * with execute permissions as they are probably shared libraries.
1911          */
1912         if (page_mapcount(page) != 1 && page_is_file_cache(page) &&
1913             (vma->vm_flags & VM_EXEC))
1914                 goto out;
1915
1916         /*
1917          * Also do not migrate dirty pages as not all filesystems can move
1918          * dirty pages in MIGRATE_ASYNC mode which is a waste of cycles.
1919          */
1920         if (page_is_file_cache(page) && PageDirty(page))
1921                 goto out;
1922
1923         isolated = numamigrate_isolate_page(pgdat, page);
1924         if (!isolated)
1925                 goto out;
1926
1927         list_add(&page->lru, &migratepages);
1928         nr_remaining = migrate_pages(&migratepages, alloc_misplaced_dst_page,
1929                                      NULL, node, MIGRATE_ASYNC,
1930                                      MR_NUMA_MISPLACED);
1931         if (nr_remaining) {
1932                 if (!list_empty(&migratepages)) {
1933                         list_del(&page->lru);
1934                         dec_node_page_state(page, NR_ISOLATED_ANON +
1935                                         page_is_file_cache(page));
1936                         putback_lru_page(page);
1937                 }
1938                 isolated = 0;
1939         } else
1940                 count_vm_numa_event(NUMA_PAGE_MIGRATE);
1941         BUG_ON(!list_empty(&migratepages));
1942         return isolated;
1943
1944 out:
1945         put_page(page);
1946         return 0;
1947 }
1948 #endif /* CONFIG_NUMA_BALANCING */
1949
1950 #if defined(CONFIG_NUMA_BALANCING) && defined(CONFIG_TRANSPARENT_HUGEPAGE)
1951 /*
1952  * Migrates a THP to a given target node. page must be locked and is unlocked
1953  * before returning.
1954  */
1955 int migrate_misplaced_transhuge_page(struct mm_struct *mm,
1956                                 struct vm_area_struct *vma,
1957                                 pmd_t *pmd, pmd_t entry,
1958                                 unsigned long address,
1959                                 struct page *page, int node)
1960 {
1961         spinlock_t *ptl;
1962         pg_data_t *pgdat = NODE_DATA(node);
1963         int isolated = 0;
1964         struct page *new_page = NULL;
1965         int page_lru = page_is_file_cache(page);
1966         unsigned long start = address & HPAGE_PMD_MASK;
1967
1968         new_page = alloc_pages_node(node,
1969                 (GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
1970                 HPAGE_PMD_ORDER);
1971         if (!new_page)
1972                 goto out_fail;
1973         prep_transhuge_page(new_page);
1974
1975         isolated = numamigrate_isolate_page(pgdat, page);
1976         if (!isolated) {
1977                 put_page(new_page);
1978                 goto out_fail;
1979         }
1980
1981         /* Prepare a page as a migration target */
1982         __SetPageLocked(new_page);
1983         if (PageSwapBacked(page))
1984                 __SetPageSwapBacked(new_page);
1985
1986         /* anon mapping, we can simply copy page->mapping to the new page: */
1987         new_page->mapping = page->mapping;
1988         new_page->index = page->index;
1989         /* flush the cache before copying using the kernel virtual address */
1990         flush_cache_range(vma, start, start + HPAGE_PMD_SIZE);
1991         migrate_page_copy(new_page, page);
1992         WARN_ON(PageLRU(new_page));
1993
1994         /* Recheck the target PMD */
1995         ptl = pmd_lock(mm, pmd);
1996         if (unlikely(!pmd_same(*pmd, entry) || !page_ref_freeze(page, 2))) {
1997                 spin_unlock(ptl);
1998
1999                 /* Reverse changes made by migrate_page_copy() */
2000                 if (TestClearPageActive(new_page))
2001                         SetPageActive(page);
2002                 if (TestClearPageUnevictable(new_page))
2003                         SetPageUnevictable(page);
2004
2005                 unlock_page(new_page);
2006                 put_page(new_page);             /* Free it */
2007
2008                 /* Retake the callers reference and putback on LRU */
2009                 get_page(page);
2010                 putback_lru_page(page);
2011                 mod_node_page_state(page_pgdat(page),
2012                          NR_ISOLATED_ANON + page_lru, -HPAGE_PMD_NR);
2013
2014                 goto out_unlock;
2015         }
2016
2017         entry = mk_huge_pmd(new_page, vma->vm_page_prot);
2018         entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
2019
2020         /*
2021          * Overwrite the old entry under pagetable lock and establish
2022          * the new PTE. Any parallel GUP will either observe the old
2023          * page blocking on the page lock, block on the page table
2024          * lock or observe the new page. The SetPageUptodate on the
2025          * new page and page_add_new_anon_rmap guarantee the copy is
2026          * visible before the pagetable update.
2027          */
2028         page_add_anon_rmap(new_page, vma, start, true);
2029         /*
2030          * At this point the pmd is numa/protnone (i.e. non present) and the TLB
2031          * has already been flushed globally.  So no TLB can be currently
2032          * caching this non present pmd mapping.  There's no need to clear the
2033          * pmd before doing set_pmd_at(), nor to flush the TLB after
2034          * set_pmd_at().  Clearing the pmd here would introduce a race
2035          * condition against MADV_DONTNEED, because MADV_DONTNEED only holds the
2036          * mmap_sem for reading.  If the pmd is set to NULL at any given time,
2037          * MADV_DONTNEED won't wait on the pmd lock and it'll skip clearing this
2038          * pmd.
2039          */
2040         set_pmd_at(mm, start, pmd, entry);
2041         update_mmu_cache_pmd(vma, address, &entry);
2042
2043         page_ref_unfreeze(page, 2);
2044         mlock_migrate_page(new_page, page);
2045         page_remove_rmap(page, true);
2046         set_page_owner_migrate_reason(new_page, MR_NUMA_MISPLACED);
2047
2048         spin_unlock(ptl);
2049
2050         /* Take an "isolate" reference and put new page on the LRU. */
2051         get_page(new_page);
2052         putback_lru_page(new_page);
2053
2054         unlock_page(new_page);
2055         unlock_page(page);
2056         put_page(page);                 /* Drop the rmap reference */
2057         put_page(page);                 /* Drop the LRU isolation reference */
2058
2059         count_vm_events(PGMIGRATE_SUCCESS, HPAGE_PMD_NR);
2060         count_vm_numa_events(NUMA_PAGE_MIGRATE, HPAGE_PMD_NR);
2061
2062         mod_node_page_state(page_pgdat(page),
2063                         NR_ISOLATED_ANON + page_lru,
2064                         -HPAGE_PMD_NR);
2065         return isolated;
2066
2067 out_fail:
2068         count_vm_events(PGMIGRATE_FAIL, HPAGE_PMD_NR);
2069         ptl = pmd_lock(mm, pmd);
2070         if (pmd_same(*pmd, entry)) {
2071                 entry = pmd_modify(entry, vma->vm_page_prot);
2072                 set_pmd_at(mm, start, pmd, entry);
2073                 update_mmu_cache_pmd(vma, address, &entry);
2074         }
2075         spin_unlock(ptl);
2076
2077 out_unlock:
2078         unlock_page(page);
2079         put_page(page);
2080         return 0;
2081 }
2082 #endif /* CONFIG_NUMA_BALANCING */
2083
2084 #endif /* CONFIG_NUMA */
2085
2086 #if defined(CONFIG_MIGRATE_VMA_HELPER)
2087 struct migrate_vma {
2088         struct vm_area_struct   *vma;
2089         unsigned long           *dst;
2090         unsigned long           *src;
2091         unsigned long           cpages;
2092         unsigned long           npages;
2093         unsigned long           start;
2094         unsigned long           end;
2095 };
2096
2097 static int migrate_vma_collect_hole(unsigned long start,
2098                                     unsigned long end,
2099                                     struct mm_walk *walk)
2100 {
2101         struct migrate_vma *migrate = walk->private;
2102         unsigned long addr;
2103
2104         for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
2105                 migrate->src[migrate->npages] = MIGRATE_PFN_MIGRATE;
2106                 migrate->dst[migrate->npages] = 0;
2107                 migrate->npages++;
2108                 migrate->cpages++;
2109         }
2110
2111         return 0;
2112 }
2113
2114 static int migrate_vma_collect_skip(unsigned long start,
2115                                     unsigned long end,
2116                                     struct mm_walk *walk)
2117 {
2118         struct migrate_vma *migrate = walk->private;
2119         unsigned long addr;
2120
2121         for (addr = start & PAGE_MASK; addr < end; addr += PAGE_SIZE) {
2122                 migrate->dst[migrate->npages] = 0;
2123                 migrate->src[migrate->npages++] = 0;
2124         }
2125
2126         return 0;
2127 }
2128
2129 static int migrate_vma_collect_pmd(pmd_t *pmdp,
2130                                    unsigned long start,
2131                                    unsigned long end,
2132                                    struct mm_walk *walk)
2133 {
2134         struct migrate_vma *migrate = walk->private;
2135         struct vm_area_struct *vma = walk->vma;
2136         struct mm_struct *mm = vma->vm_mm;
2137         unsigned long addr = start, unmapped = 0;
2138         spinlock_t *ptl;
2139         pte_t *ptep;
2140
2141 again:
2142         if (pmd_none(*pmdp))
2143                 return migrate_vma_collect_hole(start, end, walk);
2144
2145         if (pmd_trans_huge(*pmdp)) {
2146                 struct page *page;
2147
2148                 ptl = pmd_lock(mm, pmdp);
2149                 if (unlikely(!pmd_trans_huge(*pmdp))) {
2150                         spin_unlock(ptl);
2151                         goto again;
2152                 }
2153
2154                 page = pmd_page(*pmdp);
2155                 if (is_huge_zero_page(page)) {
2156                         spin_unlock(ptl);
2157                         split_huge_pmd(vma, pmdp, addr);
2158                         if (pmd_trans_unstable(pmdp))
2159                                 return migrate_vma_collect_skip(start, end,
2160                                                                 walk);
2161                 } else {
2162                         int ret;
2163
2164                         get_page(page);
2165                         spin_unlock(ptl);
2166                         if (unlikely(!trylock_page(page)))
2167                                 return migrate_vma_collect_skip(start, end,
2168                                                                 walk);
2169                         ret = split_huge_page(page);
2170                         unlock_page(page);
2171                         put_page(page);
2172                         if (ret)
2173                                 return migrate_vma_collect_skip(start, end,
2174                                                                 walk);
2175                         if (pmd_none(*pmdp))
2176                                 return migrate_vma_collect_hole(start, end,
2177                                                                 walk);
2178                 }
2179         }
2180
2181         if (unlikely(pmd_bad(*pmdp)))
2182                 return migrate_vma_collect_skip(start, end, walk);
2183
2184         ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
2185         arch_enter_lazy_mmu_mode();
2186
2187         for (; addr < end; addr += PAGE_SIZE, ptep++) {
2188                 unsigned long mpfn, pfn;
2189                 struct page *page;
2190                 swp_entry_t entry;
2191                 pte_t pte;
2192
2193                 pte = *ptep;
2194                 pfn = pte_pfn(pte);
2195
2196                 if (pte_none(pte)) {
2197                         mpfn = MIGRATE_PFN_MIGRATE;
2198                         migrate->cpages++;
2199                         pfn = 0;
2200                         goto next;
2201                 }
2202
2203                 if (!pte_present(pte)) {
2204                         mpfn = pfn = 0;
2205
2206                         /*
2207                          * Only care about unaddressable device page special
2208                          * page table entry. Other special swap entries are not
2209                          * migratable, and we ignore regular swapped page.
2210                          */
2211                         entry = pte_to_swp_entry(pte);
2212                         if (!is_device_private_entry(entry))
2213                                 goto next;
2214
2215                         page = device_private_entry_to_page(entry);
2216                         mpfn = migrate_pfn(page_to_pfn(page))|
2217                                 MIGRATE_PFN_DEVICE | MIGRATE_PFN_MIGRATE;
2218                         if (is_write_device_private_entry(entry))
2219                                 mpfn |= MIGRATE_PFN_WRITE;
2220                 } else {
2221                         if (is_zero_pfn(pfn)) {
2222                                 mpfn = MIGRATE_PFN_MIGRATE;
2223                                 migrate->cpages++;
2224                                 pfn = 0;
2225                                 goto next;
2226                         }
2227                         page = _vm_normal_page(migrate->vma, addr, pte, true);
2228                         mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
2229                         mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
2230                 }
2231
2232                 /* FIXME support THP */
2233                 if (!page || !page->mapping || PageTransCompound(page)) {
2234                         mpfn = pfn = 0;
2235                         goto next;
2236                 }
2237                 pfn = page_to_pfn(page);
2238
2239                 /*
2240                  * By getting a reference on the page we pin it and that blocks
2241                  * any kind of migration. Side effect is that it "freezes" the
2242                  * pte.
2243                  *
2244                  * We drop this reference after isolating the page from the lru
2245                  * for non device page (device page are not on the lru and thus
2246                  * can't be dropped from it).
2247                  */
2248                 get_page(page);
2249                 migrate->cpages++;
2250
2251                 /*
2252                  * Optimize for the common case where page is only mapped once
2253                  * in one process. If we can lock the page, then we can safely
2254                  * set up a special migration page table entry now.
2255                  */
2256                 if (trylock_page(page)) {
2257                         pte_t swp_pte;
2258
2259                         mpfn |= MIGRATE_PFN_LOCKED;
2260                         ptep_get_and_clear(mm, addr, ptep);
2261
2262                         /* Setup special migration page table entry */
2263                         entry = make_migration_entry(page, mpfn &
2264                                                      MIGRATE_PFN_WRITE);
2265                         swp_pte = swp_entry_to_pte(entry);
2266                         if (pte_soft_dirty(pte))
2267                                 swp_pte = pte_swp_mksoft_dirty(swp_pte);
2268                         set_pte_at(mm, addr, ptep, swp_pte);
2269
2270                         /*
2271                          * This is like regular unmap: we remove the rmap and
2272                          * drop page refcount. Page won't be freed, as we took
2273                          * a reference just above.
2274                          */
2275                         page_remove_rmap(page, false);
2276                         put_page(page);
2277
2278                         if (pte_present(pte))
2279                                 unmapped++;
2280                 }
2281
2282 next:
2283                 migrate->dst[migrate->npages] = 0;
2284                 migrate->src[migrate->npages++] = mpfn;
2285         }
2286         arch_leave_lazy_mmu_mode();
2287         pte_unmap_unlock(ptep - 1, ptl);
2288
2289         /* Only flush the TLB if we actually modified any entries */
2290         if (unmapped)
2291                 flush_tlb_range(walk->vma, start, end);
2292
2293         return 0;
2294 }
2295
2296 /*
2297  * migrate_vma_collect() - collect pages over a range of virtual addresses
2298  * @migrate: migrate struct containing all migration information
2299  *
2300  * This will walk the CPU page table. For each virtual address backed by a
2301  * valid page, it updates the src array and takes a reference on the page, in
2302  * order to pin the page until we lock it and unmap it.
2303  */
2304 static void migrate_vma_collect(struct migrate_vma *migrate)
2305 {
2306         struct mm_walk mm_walk;
2307
2308         mm_walk.pmd_entry = migrate_vma_collect_pmd;
2309         mm_walk.pte_entry = NULL;
2310         mm_walk.pte_hole = migrate_vma_collect_hole;
2311         mm_walk.hugetlb_entry = NULL;
2312         mm_walk.test_walk = NULL;
2313         mm_walk.vma = migrate->vma;
2314         mm_walk.mm = migrate->vma->vm_mm;
2315         mm_walk.private = migrate;
2316
2317         mmu_notifier_invalidate_range_start(mm_walk.mm,
2318                                             migrate->start,
2319                                             migrate->end);
2320         walk_page_range(migrate->start, migrate->end, &mm_walk);
2321         mmu_notifier_invalidate_range_end(mm_walk.mm,
2322                                           migrate->start,
2323                                           migrate->end);
2324
2325         migrate->end = migrate->start + (migrate->npages << PAGE_SHIFT);
2326 }
2327
2328 /*
2329  * migrate_vma_check_page() - check if page is pinned or not
2330  * @page: struct page to check
2331  *
2332  * Pinned pages cannot be migrated. This is the same test as in
2333  * migrate_page_move_mapping(), except that here we allow migration of a
2334  * ZONE_DEVICE page.
2335  */
2336 static bool migrate_vma_check_page(struct page *page)
2337 {
2338         /*
2339          * One extra ref because caller holds an extra reference, either from
2340          * isolate_lru_page() for a regular page, or migrate_vma_collect() for
2341          * a device page.
2342          */
2343         int extra = 1;
2344
2345         /*
2346          * FIXME support THP (transparent huge page), it is bit more complex to
2347          * check them than regular pages, because they can be mapped with a pmd
2348          * or with a pte (split pte mapping).
2349          */
2350         if (PageCompound(page))
2351                 return false;
2352
2353         /* Page from ZONE_DEVICE have one extra reference */
2354         if (is_zone_device_page(page)) {
2355                 /*
2356                  * Private page can never be pin as they have no valid pte and
2357                  * GUP will fail for those. Yet if there is a pending migration
2358                  * a thread might try to wait on the pte migration entry and
2359                  * will bump the page reference count. Sadly there is no way to
2360                  * differentiate a regular pin from migration wait. Hence to
2361                  * avoid 2 racing thread trying to migrate back to CPU to enter
2362                  * infinite loop (one stoping migration because the other is
2363                  * waiting on pte migration entry). We always return true here.
2364                  *
2365                  * FIXME proper solution is to rework migration_entry_wait() so
2366                  * it does not need to take a reference on page.
2367                  */
2368                 if (is_device_private_page(page))
2369                         return true;
2370
2371                 /*
2372                  * Only allow device public page to be migrated and account for
2373                  * the extra reference count imply by ZONE_DEVICE pages.
2374                  */
2375                 if (!is_device_public_page(page))
2376                         return false;
2377                 extra++;
2378         }
2379
2380         /* For file back page */
2381         if (page_mapping(page))
2382                 extra += 1 + page_has_private(page);
2383
2384         if ((page_count(page) - extra) > page_mapcount(page))
2385                 return false;
2386
2387         return true;
2388 }
2389
2390 /*
2391  * migrate_vma_prepare() - lock pages and isolate them from the lru
2392  * @migrate: migrate struct containing all migration information
2393  *
2394  * This locks pages that have been collected by migrate_vma_collect(). Once each
2395  * page is locked it is isolated from the lru (for non-device pages). Finally,
2396  * the ref taken by migrate_vma_collect() is dropped, as locked pages cannot be
2397  * migrated by concurrent kernel threads.
2398  */
2399 static void migrate_vma_prepare(struct migrate_vma *migrate)
2400 {
2401         const unsigned long npages = migrate->npages;
2402         const unsigned long start = migrate->start;
2403         unsigned long addr, i, restore = 0;
2404         bool allow_drain = true;
2405
2406         lru_add_drain();
2407
2408         for (i = 0; (i < npages) && migrate->cpages; i++) {
2409                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2410                 bool remap = true;
2411
2412                 if (!page)
2413                         continue;
2414
2415                 if (!(migrate->src[i] & MIGRATE_PFN_LOCKED)) {
2416                         /*
2417                          * Because we are migrating several pages there can be
2418                          * a deadlock between 2 concurrent migration where each
2419                          * are waiting on each other page lock.
2420                          *
2421                          * Make migrate_vma() a best effort thing and backoff
2422                          * for any page we can not lock right away.
2423                          */
2424                         if (!trylock_page(page)) {
2425                                 migrate->src[i] = 0;
2426                                 migrate->cpages--;
2427                                 put_page(page);
2428                                 continue;
2429                         }
2430                         remap = false;
2431                         migrate->src[i] |= MIGRATE_PFN_LOCKED;
2432                 }
2433
2434                 /* ZONE_DEVICE pages are not on LRU */
2435                 if (!is_zone_device_page(page)) {
2436                         if (!PageLRU(page) && allow_drain) {
2437                                 /* Drain CPU's pagevec */
2438                                 lru_add_drain_all();
2439                                 allow_drain = false;
2440                         }
2441
2442                         if (isolate_lru_page(page)) {
2443                                 if (remap) {
2444                                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2445                                         migrate->cpages--;
2446                                         restore++;
2447                                 } else {
2448                                         migrate->src[i] = 0;
2449                                         unlock_page(page);
2450                                         migrate->cpages--;
2451                                         put_page(page);
2452                                 }
2453                                 continue;
2454                         }
2455
2456                         /* Drop the reference we took in collect */
2457                         put_page(page);
2458                 }
2459
2460                 if (!migrate_vma_check_page(page)) {
2461                         if (remap) {
2462                                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2463                                 migrate->cpages--;
2464                                 restore++;
2465
2466                                 if (!is_zone_device_page(page)) {
2467                                         get_page(page);
2468                                         putback_lru_page(page);
2469                                 }
2470                         } else {
2471                                 migrate->src[i] = 0;
2472                                 unlock_page(page);
2473                                 migrate->cpages--;
2474
2475                                 if (!is_zone_device_page(page))
2476                                         putback_lru_page(page);
2477                                 else
2478                                         put_page(page);
2479                         }
2480                 }
2481         }
2482
2483         for (i = 0, addr = start; i < npages && restore; i++, addr += PAGE_SIZE) {
2484                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2485
2486                 if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
2487                         continue;
2488
2489                 remove_migration_pte(page, migrate->vma, addr, page);
2490
2491                 migrate->src[i] = 0;
2492                 unlock_page(page);
2493                 put_page(page);
2494                 restore--;
2495         }
2496 }
2497
2498 /*
2499  * migrate_vma_unmap() - replace page mapping with special migration pte entry
2500  * @migrate: migrate struct containing all migration information
2501  *
2502  * Replace page mapping (CPU page table pte) with a special migration pte entry
2503  * and check again if it has been pinned. Pinned pages are restored because we
2504  * cannot migrate them.
2505  *
2506  * This is the last step before we call the device driver callback to allocate
2507  * destination memory and copy contents of original page over to new page.
2508  */
2509 static void migrate_vma_unmap(struct migrate_vma *migrate)
2510 {
2511         int flags = TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
2512         const unsigned long npages = migrate->npages;
2513         const unsigned long start = migrate->start;
2514         unsigned long addr, i, restore = 0;
2515
2516         for (i = 0; i < npages; i++) {
2517                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2518
2519                 if (!page || !(migrate->src[i] & MIGRATE_PFN_MIGRATE))
2520                         continue;
2521
2522                 if (page_mapped(page)) {
2523                         try_to_unmap(page, flags);
2524                         if (page_mapped(page))
2525                                 goto restore;
2526                 }
2527
2528                 if (migrate_vma_check_page(page))
2529                         continue;
2530
2531 restore:
2532                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2533                 migrate->cpages--;
2534                 restore++;
2535         }
2536
2537         for (addr = start, i = 0; i < npages && restore; addr += PAGE_SIZE, i++) {
2538                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2539
2540                 if (!page || (migrate->src[i] & MIGRATE_PFN_MIGRATE))
2541                         continue;
2542
2543                 remove_migration_ptes(page, page, false);
2544
2545                 migrate->src[i] = 0;
2546                 unlock_page(page);
2547                 restore--;
2548
2549                 if (is_zone_device_page(page))
2550                         put_page(page);
2551                 else
2552                         putback_lru_page(page);
2553         }
2554 }
2555
2556 static void migrate_vma_insert_page(struct migrate_vma *migrate,
2557                                     unsigned long addr,
2558                                     struct page *page,
2559                                     unsigned long *src,
2560                                     unsigned long *dst)
2561 {
2562         struct vm_area_struct *vma = migrate->vma;
2563         struct mm_struct *mm = vma->vm_mm;
2564         struct mem_cgroup *memcg;
2565         bool flush = false;
2566         spinlock_t *ptl;
2567         pte_t entry;
2568         pgd_t *pgdp;
2569         p4d_t *p4dp;
2570         pud_t *pudp;
2571         pmd_t *pmdp;
2572         pte_t *ptep;
2573
2574         /* Only allow populating anonymous memory */
2575         if (!vma_is_anonymous(vma))
2576                 goto abort;
2577
2578         pgdp = pgd_offset(mm, addr);
2579         p4dp = p4d_alloc(mm, pgdp, addr);
2580         if (!p4dp)
2581                 goto abort;
2582         pudp = pud_alloc(mm, p4dp, addr);
2583         if (!pudp)
2584                 goto abort;
2585         pmdp = pmd_alloc(mm, pudp, addr);
2586         if (!pmdp)
2587                 goto abort;
2588
2589         if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
2590                 goto abort;
2591
2592         /*
2593          * Use pte_alloc() instead of pte_alloc_map().  We can't run
2594          * pte_offset_map() on pmds where a huge pmd might be created
2595          * from a different thread.
2596          *
2597          * pte_alloc_map() is safe to use under down_write(mmap_sem) or when
2598          * parallel threads are excluded by other means.
2599          *
2600          * Here we only have down_read(mmap_sem).
2601          */
2602         if (pte_alloc(mm, pmdp, addr))
2603                 goto abort;
2604
2605         /* See the comment in pte_alloc_one_map() */
2606         if (unlikely(pmd_trans_unstable(pmdp)))
2607                 goto abort;
2608
2609         if (unlikely(anon_vma_prepare(vma)))
2610                 goto abort;
2611         if (mem_cgroup_try_charge(page, vma->vm_mm, GFP_KERNEL, &memcg, false))
2612                 goto abort;
2613
2614         /*
2615          * The memory barrier inside __SetPageUptodate makes sure that
2616          * preceding stores to the page contents become visible before
2617          * the set_pte_at() write.
2618          */
2619         __SetPageUptodate(page);
2620
2621         if (is_zone_device_page(page)) {
2622                 if (is_device_private_page(page)) {
2623                         swp_entry_t swp_entry;
2624
2625                         swp_entry = make_device_private_entry(page, vma->vm_flags & VM_WRITE);
2626                         entry = swp_entry_to_pte(swp_entry);
2627                 } else if (is_device_public_page(page)) {
2628                         entry = pte_mkold(mk_pte(page, READ_ONCE(vma->vm_page_prot)));
2629                         if (vma->vm_flags & VM_WRITE)
2630                                 entry = pte_mkwrite(pte_mkdirty(entry));
2631                         entry = pte_mkdevmap(entry);
2632                 }
2633         } else {
2634                 entry = mk_pte(page, vma->vm_page_prot);
2635                 if (vma->vm_flags & VM_WRITE)
2636                         entry = pte_mkwrite(pte_mkdirty(entry));
2637         }
2638
2639         ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
2640
2641         if (pte_present(*ptep)) {
2642                 unsigned long pfn = pte_pfn(*ptep);
2643
2644                 if (!is_zero_pfn(pfn)) {
2645                         pte_unmap_unlock(ptep, ptl);
2646                         mem_cgroup_cancel_charge(page, memcg, false);
2647                         goto abort;
2648                 }
2649                 flush = true;
2650         } else if (!pte_none(*ptep)) {
2651                 pte_unmap_unlock(ptep, ptl);
2652                 mem_cgroup_cancel_charge(page, memcg, false);
2653                 goto abort;
2654         }
2655
2656         /*
2657          * Check for usefaultfd but do not deliver the fault. Instead,
2658          * just back off.
2659          */
2660         if (userfaultfd_missing(vma)) {
2661                 pte_unmap_unlock(ptep, ptl);
2662                 mem_cgroup_cancel_charge(page, memcg, false);
2663                 goto abort;
2664         }
2665
2666         inc_mm_counter(mm, MM_ANONPAGES);
2667         page_add_new_anon_rmap(page, vma, addr, false);
2668         mem_cgroup_commit_charge(page, memcg, false, false);
2669         if (!is_zone_device_page(page))
2670                 lru_cache_add_active_or_unevictable(page, vma);
2671         get_page(page);
2672
2673         if (flush) {
2674                 flush_cache_page(vma, addr, pte_pfn(*ptep));
2675                 ptep_clear_flush_notify(vma, addr, ptep);
2676                 set_pte_at_notify(mm, addr, ptep, entry);
2677                 update_mmu_cache(vma, addr, ptep);
2678         } else {
2679                 /* No need to invalidate - it was non-present before */
2680                 set_pte_at(mm, addr, ptep, entry);
2681                 update_mmu_cache(vma, addr, ptep);
2682         }
2683
2684         pte_unmap_unlock(ptep, ptl);
2685         *src = MIGRATE_PFN_MIGRATE;
2686         return;
2687
2688 abort:
2689         *src &= ~MIGRATE_PFN_MIGRATE;
2690 }
2691
2692 /*
2693  * migrate_vma_pages() - migrate meta-data from src page to dst page
2694  * @migrate: migrate struct containing all migration information
2695  *
2696  * This migrates struct page meta-data from source struct page to destination
2697  * struct page. This effectively finishes the migration from source page to the
2698  * destination page.
2699  */
2700 static void migrate_vma_pages(struct migrate_vma *migrate)
2701 {
2702         const unsigned long npages = migrate->npages;
2703         const unsigned long start = migrate->start;
2704         struct vm_area_struct *vma = migrate->vma;
2705         struct mm_struct *mm = vma->vm_mm;
2706         unsigned long addr, i, mmu_start;
2707         bool notified = false;
2708
2709         for (i = 0, addr = start; i < npages; addr += PAGE_SIZE, i++) {
2710                 struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
2711                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2712                 struct address_space *mapping;
2713                 int r;
2714
2715                 if (!newpage) {
2716                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2717                         continue;
2718                 }
2719
2720                 if (!page) {
2721                         if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE)) {
2722                                 continue;
2723                         }
2724                         if (!notified) {
2725                                 mmu_start = addr;
2726                                 notified = true;
2727                                 mmu_notifier_invalidate_range_start(mm,
2728                                                                 mmu_start,
2729                                                                 migrate->end);
2730                         }
2731                         migrate_vma_insert_page(migrate, addr, newpage,
2732                                                 &migrate->src[i],
2733                                                 &migrate->dst[i]);
2734                         continue;
2735                 }
2736
2737                 mapping = page_mapping(page);
2738
2739                 if (is_zone_device_page(newpage)) {
2740                         if (is_device_private_page(newpage)) {
2741                                 /*
2742                                  * For now only support private anonymous when
2743                                  * migrating to un-addressable device memory.
2744                                  */
2745                                 if (mapping) {
2746                                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2747                                         continue;
2748                                 }
2749                         } else if (!is_device_public_page(newpage)) {
2750                                 /*
2751                                  * Other types of ZONE_DEVICE page are not
2752                                  * supported.
2753                                  */
2754                                 migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2755                                 continue;
2756                         }
2757                 }
2758
2759                 r = migrate_page(mapping, newpage, page, MIGRATE_SYNC_NO_COPY);
2760                 if (r != MIGRATEPAGE_SUCCESS)
2761                         migrate->src[i] &= ~MIGRATE_PFN_MIGRATE;
2762         }
2763
2764         /*
2765          * No need to double call mmu_notifier->invalidate_range() callback as
2766          * the above ptep_clear_flush_notify() inside migrate_vma_insert_page()
2767          * did already call it.
2768          */
2769         if (notified)
2770                 mmu_notifier_invalidate_range_only_end(mm, mmu_start,
2771                                                        migrate->end);
2772 }
2773
2774 /*
2775  * migrate_vma_finalize() - restore CPU page table entry
2776  * @migrate: migrate struct containing all migration information
2777  *
2778  * This replaces the special migration pte entry with either a mapping to the
2779  * new page if migration was successful for that page, or to the original page
2780  * otherwise.
2781  *
2782  * This also unlocks the pages and puts them back on the lru, or drops the extra
2783  * refcount, for device pages.
2784  */
2785 static void migrate_vma_finalize(struct migrate_vma *migrate)
2786 {
2787         const unsigned long npages = migrate->npages;
2788         unsigned long i;
2789
2790         for (i = 0; i < npages; i++) {
2791                 struct page *newpage = migrate_pfn_to_page(migrate->dst[i]);
2792                 struct page *page = migrate_pfn_to_page(migrate->src[i]);
2793
2794                 if (!page) {
2795                         if (newpage) {
2796                                 unlock_page(newpage);
2797                                 put_page(newpage);
2798                         }
2799                         continue;
2800                 }
2801
2802                 if (!(migrate->src[i] & MIGRATE_PFN_MIGRATE) || !newpage) {
2803                         if (newpage) {
2804                                 unlock_page(newpage);
2805                                 put_page(newpage);
2806                         }
2807                         newpage = page;
2808                 }
2809
2810                 remove_migration_ptes(page, newpage, false);
2811                 unlock_page(page);
2812                 migrate->cpages--;
2813
2814                 if (is_zone_device_page(page))
2815                         put_page(page);
2816                 else
2817                         putback_lru_page(page);
2818
2819                 if (newpage != page) {
2820                         unlock_page(newpage);
2821                         if (is_zone_device_page(newpage))
2822                                 put_page(newpage);
2823                         else
2824                                 putback_lru_page(newpage);
2825                 }
2826         }
2827 }
2828
2829 /*
2830  * migrate_vma() - migrate a range of memory inside vma
2831  *
2832  * @ops: migration callback for allocating destination memory and copying
2833  * @vma: virtual memory area containing the range to be migrated
2834  * @start: start address of the range to migrate (inclusive)
2835  * @end: end address of the range to migrate (exclusive)
2836  * @src: array of hmm_pfn_t containing source pfns
2837  * @dst: array of hmm_pfn_t containing destination pfns
2838  * @private: pointer passed back to each of the callback
2839  * Returns: 0 on success, error code otherwise
2840  *
2841  * This function tries to migrate a range of memory virtual address range, using
2842  * callbacks to allocate and copy memory from source to destination. First it
2843  * collects all the pages backing each virtual address in the range, saving this
2844  * inside the src array. Then it locks those pages and unmaps them. Once the pages
2845  * are locked and unmapped, it checks whether each page is pinned or not. Pages
2846  * that aren't pinned have the MIGRATE_PFN_MIGRATE flag set (by this function)
2847  * in the corresponding src array entry. It then restores any pages that are
2848  * pinned, by remapping and unlocking those pages.
2849  *
2850  * At this point it calls the alloc_and_copy() callback. For documentation on
2851  * what is expected from that callback, see struct migrate_vma_ops comments in
2852  * include/linux/migrate.h
2853  *
2854  * After the alloc_and_copy() callback, this function goes over each entry in
2855  * the src array that has the MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag
2856  * set. If the corresponding entry in dst array has MIGRATE_PFN_VALID flag set,
2857  * then the function tries to migrate struct page information from the source
2858  * struct page to the destination struct page. If it fails to migrate the struct
2859  * page information, then it clears the MIGRATE_PFN_MIGRATE flag in the src
2860  * array.
2861  *
2862  * At this point all successfully migrated pages have an entry in the src
2863  * array with MIGRATE_PFN_VALID and MIGRATE_PFN_MIGRATE flag set and the dst
2864  * array entry with MIGRATE_PFN_VALID flag set.
2865  *
2866  * It then calls the finalize_and_map() callback. See comments for "struct
2867  * migrate_vma_ops", in include/linux/migrate.h for details about
2868  * finalize_and_map() behavior.
2869  *
2870  * After the finalize_and_map() callback, for successfully migrated pages, this
2871  * function updates the CPU page table to point to new pages, otherwise it
2872  * restores the CPU page table to point to the original source pages.
2873  *
2874  * Function returns 0 after the above steps, even if no pages were migrated
2875  * (The function only returns an error if any of the arguments are invalid.)
2876  *
2877  * Both src and dst array must be big enough for (end - start) >> PAGE_SHIFT
2878  * unsigned long entries.
2879  */
2880 int migrate_vma(const struct migrate_vma_ops *ops,
2881                 struct vm_area_struct *vma,
2882                 unsigned long start,
2883                 unsigned long end,
2884                 unsigned long *src,
2885                 unsigned long *dst,
2886                 void *private)
2887 {
2888         struct migrate_vma migrate;
2889
2890         /* Sanity check the arguments */
2891         start &= PAGE_MASK;
2892         end &= PAGE_MASK;
2893         if (!vma || is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL) ||
2894                         vma_is_dax(vma))
2895                 return -EINVAL;
2896         if (start < vma->vm_start || start >= vma->vm_end)
2897                 return -EINVAL;
2898         if (end <= vma->vm_start || end > vma->vm_end)
2899                 return -EINVAL;
2900         if (!ops || !src || !dst || start >= end)
2901                 return -EINVAL;
2902
2903         memset(src, 0, sizeof(*src) * ((end - start) >> PAGE_SHIFT));
2904         migrate.src = src;
2905         migrate.dst = dst;
2906         migrate.start = start;
2907         migrate.npages = 0;
2908         migrate.cpages = 0;
2909         migrate.end = end;
2910         migrate.vma = vma;
2911
2912         /* Collect, and try to unmap source pages */
2913         migrate_vma_collect(&migrate);
2914         if (!migrate.cpages)
2915                 return 0;
2916
2917         /* Lock and isolate page */
2918         migrate_vma_prepare(&migrate);
2919         if (!migrate.cpages)
2920                 return 0;
2921
2922         /* Unmap pages */
2923         migrate_vma_unmap(&migrate);
2924         if (!migrate.cpages)
2925                 return 0;
2926
2927         /*
2928          * At this point pages are locked and unmapped, and thus they have
2929          * stable content and can safely be copied to destination memory that
2930          * is allocated by the callback.
2931          *
2932          * Note that migration can fail in migrate_vma_struct_page() for each
2933          * individual page.
2934          */
2935         ops->alloc_and_copy(vma, src, dst, start, end, private);
2936
2937         /* This does the real migration of struct page */
2938         migrate_vma_pages(&migrate);
2939
2940         ops->finalize_and_map(vma, src, dst, start, end, private);
2941
2942         /* Unlock and remap pages */
2943         migrate_vma_finalize(&migrate);
2944
2945         return 0;
2946 }
2947 EXPORT_SYMBOL(migrate_vma);
2948 #endif /* defined(MIGRATE_VMA_HELPER) */