On Mon, Aug 24, 2020 at 06:31:28PM +1000, Alistair Popple wrote:
During memory migration a pte is temporarily replaced with a migration swap pte. Some pte bits from the existing mapping such as the soft-dirty and uffd write-protect bits are preserved by copying these to the temporary migration swap pte.
However these bits are not stored at the same location for swap and non-swap ptes. Therefore testing these bits requires using the appropriate helper function for the given pte type.
Unfortunately several code locations were found where the wrong helper function is being used to test soft_dirty and uffd_wp bits which leads to them getting incorrectly set or cleared during page-migration.
Fix these by using the correct tests based on pte type.
Fixes: a5430dda8a3a ("mm/migrate: support un-addressable ZONE_DEVICE page in migration") Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration") Signed-off-by: Alistair Popple alistair@popple.id.au Cc: stable@vger.kernel.org
mm/migrate.c | 6 ++++-- mm/rmap.c | 9 +++++++-- 2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c index ddb64253fe3e..5bea19c496af 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -2427,9 +2427,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, entry = make_migration_entry(page, mpfn & MIGRATE_PFN_WRITE); swp_pte = swp_entry_to_pte(entry);
if (pte_soft_dirty(pte))
if ((is_swap_pte(pte) && pte_swp_soft_dirty(pte))|| (!is_swap_pte(pte) && pte_soft_dirty(pte))) swp_pte = pte_swp_mksoft_dirty(swp_pte);
if (pte_uffd_wp(pte))
if ((is_swap_pte(pte) && pte_swp_uffd_wp(pte))|| (!is_swap_pte(pte) && pte_uffd_wp(pte))) swp_pte = pte_swp_mkuffd_wp(swp_pte); set_pte_at(mm, addr, ptep, swp_pte);
The worst case is we'll call is_swap_pte() four times for each entry. Also considering we know it's not a pte_none() when reach here, how about:
if (pte_present(pte)) { // pte handling of both soft dirty and uffd-wp } else { // swap handling of both soft dirty and uffd-wp }
?
Thanks,