From: Ralph Campbell <rcampbell@xxxxxxxxxx> Subject: mm/migrate: properly preserve write attribute in special migrate entry Use of pte_write(pte) is only valid for present pte, the common code which set the migration entry can be reach for both valid present pte and special swap entry (for device memory). Fix the code to use the mpfn value which properly handle both cases. On x86 this did not have any bad side effect because pte write bit is below PAGE_BIT_GLOBAL and thus special swap entry have it set to 0 which in turn means we were always creating read only special migration entry. So once migration did finish we always write protected the CPU page table entry (moreover this is only an issue when migrating from device memory to system memory). End effect is that CPU write access would fault again and restore write permission. This behaviour isn't too bad; it just burns CPU cycles by forcing CPU to take a second fault on write access. ie, double faulting the same address. There is no corruption or incorrect states (it behaves as a COWed page from a fork with a mapcount of 1). Link: http://lkml.kernel.org/r/20180402023506.12180-1-jglisse@xxxxxxxxxx Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/migrate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff -puN mm/migrate.c~mm-migrate-properly-preserve-write-attribute-in-special-migrate-entry mm/migrate.c --- a/mm/migrate.c~mm-migrate-properly-preserve-write-attribute-in-special-migrate-entry +++ a/mm/migrate.c @@ -2346,7 +2346,8 @@ again: ptep_get_and_clear(mm, addr, ptep); /* Setup special migration page table entry */ - entry = make_migration_entry(page, pte_write(pte)); + entry = make_migration_entry(page, mpfn & + MIGRATE_PFN_WRITE); swp_pte = swp_entry_to_pte(entry); if (pte_soft_dirty(pte)) swp_pte = pte_swp_mksoft_dirty(swp_pte); _ -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
