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 <[email protected]>
Acked-by: Peter Xu <[email protected]>
Reviewed-by: "Huang, Ying" <[email protected]>
Reported-by: "Huang, Ying" <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Cc: Alex Sierra <[email protected]>
Cc: Ben Skeggs <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: huang ying <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: John Hubbard <[email protected]>
Cc: Karol Herbst <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Ralph Campbell <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions