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Subject[PATCH 3.16 147/178] s390/mm: fix CMMA vs KSM vs others
3.16.46-rc1 review patch.  If anyone has any objections, please let me know.


From: Christian Borntraeger <>

commit a8f60d1fadf7b8b54449fcc9d6b15248917478ba upstream.

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.

Signed-of-by: Christian Borntraeger <>
Signed-off-by: Martin Schwidefsky <>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <>
arch/s390/include/asm/pgtable.h | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -868,6 +868,8 @@ static inline void set_pte_at(struct mm_
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;
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