On heavy paging with KSM I see guest data corruption. Turns out that
KSM will add pages to its tree, where the mapping return true for
pte_unused (or might become as such later). KSM will unmap such pages
and reinstantiate with different attributes (e.g. write protected or
special, e.g. in replace_page or write_protect_page)). This uncovered
a bug in our pagetable handling: We must remove the unused flag as
soon as an entry becomes present again.
upstream commit id: a8f60d1fadf7b8b54449fcc9d6b15248917478ba
Cc: stable@xxxxxxxxxxxxxxx
Signed-of-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
(cherry picked from commit a8f60d1fadf7b8b54449fcc9d6b15248917478ba)
Signed-of-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
[backport for 4.4]
---
arch/s390/include/asm/pgtable.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 024f85f..e2c0e4e 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -829,6 +829,8 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
{
pgste_t pgste;
+ if (pte_present(entry))
+ pte_val(entry) &= ~_PAGE_UNUSED;
if (mm_has_pgste(mm)) {
pgste = pgste_get_lock(ptep);
pgste_val(pgste) &= ~_PGSTE_GPS_ZERO;
--
2.7.4