The patch titled Subject: mm/migrate_device.c: copy pte dirty bit to page has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Alistair Popple apopple@nvidia.com Subject: mm/migrate_device.c: copy pte dirty bit to page Date: Fri, 2 Sep 2022 10:35:53 +1000

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/dd48e4882ce859c295c1a77612f66d198b0403f9.166207852... Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") Signed-off-by: Alistair Popple apopple@nvidia.com Acked-by: Peter Xu peterx@redhat.com Reviewed-by: "Huang, Ying" ying.huang@intel.com Reported-by: "Huang, Ying" ying.huang@intel.com Acked-by: David 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: Andrew Morton akpm@linux-foundation.org ---

mm/migrate_device.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/mm/migrate_device.c~mm-migrate_devicec-copy-pte-dirty-bit-to-page +++ a/mm/migrate_device.c @@ -7,6 +7,7 @@ #include <linux/export.h> #include <linux/memremap.h> #include <linux/migrate.h> +#include <linux/mm.h> #include <linux/mm_inline.h> #include <linux/mmu_notifier.h> #include <linux/oom.h> @@ -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( _

Patches currently in -mm which might be from apopple@nvidia.com are

mm-migrate_devicec-flush-tlb-while-holding-ptl.patch mm-migrate_devicec-add-missing-flush_cache_page.patch mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch mm-gupc-simplify-and-fix-check_and_migrate_movable_pages-return-codes.patch selftests-hmm-tests-add-test-for-dirty-bits.patch mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch mm-gupc-refactor-check_and_migrate_movable_pages.patch mm-migrate_devicec-fix-a-misleading-and-out-dated-comment.patch