Commit fd35ca3d authored by Alistair Popple's avatar Alistair Popple Committed by Andrew Morton

mm/migrate_device.c: copy pte dirty bit to page

migrate_vma_setup() has a fast path in migrate_vma_collect_pmd() that
installs migration entries directly if it can lock the migrating page. 
When removing a dirty pte the dirty bit is supposed to be carried over to
the underlying page to prevent it being lost.

Currently migrate_vma_*() can only be used for private anonymous mappings.
That means loss of the dirty bit usually doesn't result in data loss
because these pages are typically not file-backed.  However pages may be
backed by swap storage which can result in data loss if an attempt is made
to migrate a dirty page that doesn't yet have the PageDirty flag set.

In this case migration will fail due to unexpected references but the
dirty pte bit will be lost.  If the page is subsequently reclaimed data
won't be written back to swap storage as it is considered uptodate,
resulting in data loss if the page is subsequently accessed.

Prevent this by copying the dirty bit to the page when removing the pte to
match what try_to_migrate_one() does.

Link: https://lkml.kernel.org/r/dd48e4882ce859c295c1a77612f66d198b0403f9.1662078528.git-series.apopple@nvidia.com
Fixes: 8c3328f1 ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Signed-off-by: default avatarAlistair Popple <apopple@nvidia.com>
Acked-by: default avatarPeter Xu <peterx@redhat.com>
Reviewed-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Reported-by: default avatar"Huang, Ying" <ying.huang@intel.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Alex Sierra <alex.sierra@amd.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: huang ying <huang.ying.caritas@gmail.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Karol Herbst <kherbst@redhat.com>
Cc: Logan Gunthorpe <logang@deltatee.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Nadav Amit <nadav.amit@gmail.com>
Cc: Paul Mackerras <paulus@ozlabs.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a3589e1d
...@@ -7,6 +7,7 @@ ...@@ -7,6 +7,7 @@
#include <linux/export.h> #include <linux/export.h>
#include <linux/memremap.h> #include <linux/memremap.h>
#include <linux/migrate.h> #include <linux/migrate.h>
#include <linux/mm.h>
#include <linux/mm_inline.h> #include <linux/mm_inline.h>
#include <linux/mmu_notifier.h> #include <linux/mmu_notifier.h>
#include <linux/oom.h> #include <linux/oom.h>
...@@ -196,7 +197,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, ...@@ -196,7 +197,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
flush_cache_page(vma, addr, pte_pfn(*ptep)); flush_cache_page(vma, addr, pte_pfn(*ptep));
anon_exclusive = PageAnon(page) && PageAnonExclusive(page); anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
if (anon_exclusive) { if (anon_exclusive) {
ptep_clear_flush(vma, addr, ptep); pte = ptep_clear_flush(vma, addr, ptep);
if (page_try_share_anon_rmap(page)) { if (page_try_share_anon_rmap(page)) {
set_pte_at(mm, addr, ptep, pte); set_pte_at(mm, addr, ptep, pte);
...@@ -206,11 +207,15 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, ...@@ -206,11 +207,15 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
goto next; goto next;
} }
} else { } else {
ptep_get_and_clear(mm, addr, ptep); pte = ptep_get_and_clear(mm, addr, ptep);
} }
migrate->cpages++; migrate->cpages++;
/* Set the dirty flag on the folio now the pte is gone. */
if (pte_dirty(pte))
folio_mark_dirty(page_folio(page));
/* Setup special migration page table entry */ /* Setup special migration page table entry */
if (mpfn & MIGRATE_PFN_WRITE) if (mpfn & MIGRATE_PFN_WRITE)
entry = make_writable_migration_entry( entry = make_writable_migration_entry(
......
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