From fd35ca3d12cc9922d7d9a35f934e72132dbc4853 Mon Sep 17 00:00:00 2001 From: Alistair Popple Date: Fri, 2 Sep 2022 10:35:53 +1000 Subject: 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: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") Signed-off-by: Alistair Popple Acked-by: Peter Xu Reviewed-by: "Huang, Ying" Reported-by: "Huang, Ying" Acked-by: David Hildenbrand Cc: Alex Sierra Cc: Ben Skeggs Cc: Felix Kuehling Cc: huang ying Cc: Jason Gunthorpe Cc: John Hubbard Cc: Karol Herbst Cc: Logan Gunthorpe Cc: Lyude Paul Cc: Matthew Wilcox Cc: Nadav Amit Cc: Paul Mackerras Cc: Ralph Campbell Cc: Signed-off-by: Andrew Morton --- mm/migrate_device.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'mm/migrate_device.c') diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 4cc849c3b54c..dbf6c7a7a7c9 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -196,7 +197,7 @@ again: flush_cache_page(vma, addr, pte_pfn(*ptep)); anon_exclusive = PageAnon(page) && PageAnonExclusive(page); if (anon_exclusive) { - ptep_clear_flush(vma, addr, ptep); + pte = ptep_clear_flush(vma, addr, ptep); if (page_try_share_anon_rmap(page)) { set_pte_at(mm, addr, ptep, pte); @@ -206,11 +207,15 @@ again: goto next; } } else { - ptep_get_and_clear(mm, addr, ptep); + pte = ptep_get_and_clear(mm, addr, ptep); } 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 */ if (mpfn & MIGRATE_PFN_WRITE) entry = make_writable_migration_entry( -- cgit v1.2.3