The patch titled
Subject: mm/migrate: properly preserve write attribute in special migrate entry
has been removed from the -mm tree. Its filename was
mm-migrate-properly-preserve-write-attribute-in-special-migrate-entry.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
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);
_
Patches currently in -mm which might be from rcampbell@xxxxxxxxxx are
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