From 72c348fdb69125fb52deb018a4306dfe4bccfddd Mon Sep 17 00:00:00 2001 From: Alistair Popple Date: Tue, 16 Aug 2022 17:39:24 +1000 Subject: [PATCH] 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/6e77914685ede036c419fa65b6adc27f25a6c3e9.1660635033.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 Reported-by: Huang Ying Reviewed-by: Huang Ying Cc: Alex Sierra Cc: Ben Skeggs Cc: David Hildenbrand Cc: Felix Kuehling Cc: Jason Gunthorpe Cc: John Hubbard Cc: Karol Herbst Cc: Logan Gunthorpe Cc: Lyude Paul Cc: Matthew Wilcox (Oracle) Cc: Paul Mackerras Cc: Ralph Campbell Cc: Signed-off-by: Andrew Morton --- mm/migrate_device.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 27fb37d65476..e2d09e56a771 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -7,6 +7,7 @@ #include #include #include +#include #include #include #include @@ -61,7 +62,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, struct migrate_vma *migrate = walk->private; struct vm_area_struct *vma = walk->vma; struct mm_struct *mm = vma->vm_mm; - unsigned long addr = start, unmapped = 0; + unsigned long addr = start; spinlock_t *ptl; pte_t *ptep; @@ -193,11 +194,10 @@ again: bool anon_exclusive; pte_t swp_pte; + flush_cache_page(vma, addr, pte_pfn(*ptep)); + pte = ptep_clear_flush(vma, addr, ptep); anon_exclusive = PageAnon(page) && PageAnonExclusive(page); if (anon_exclusive) { - flush_cache_page(vma, addr, pte_pfn(*ptep)); - ptep_clear_flush(vma, addr, ptep); - if (page_try_share_anon_rmap(page)) { set_pte_at(mm, addr, ptep, pte); unlock_page(page); @@ -205,12 +205,14 @@ again: mpfn = 0; goto next; } - } else { - 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( @@ -242,9 +244,6 @@ again: */ page_remove_rmap(page, vma, false); put_page(page); - - if (pte_present(pte)) - unmapped++; } else { put_page(page); mpfn = 0; @@ -257,10 +256,6 @@ next: arch_leave_lazy_mmu_mode(); pte_unmap_unlock(ptep - 1, ptl); - /* Only flush the TLB if we actually modified any entries */ - if (unmapped) - flush_tlb_range(walk->vma, start, end); - return 0; } -- 2.50.1