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s390/mm: fix CMMA vs KSM vs others

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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.

Cc: stable@vger.kernel.org
Signed-of-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Christian Borntraeger 2017-04-09 22:09:38 +02:00 committed by Martin Schwidefsky
parent c08e611b7d
commit a8f60d1fad
1 changed files with 2 additions and 0 deletions
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arch/s390/include/asm/pgtable.h
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@ -1051,6 +1051,8 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
{
if (!MACHINE_HAS_NX)
pte_val(entry) &= ~_PAGE_NOEXEC;
if (pte_present(entry))
pte_val(entry) &= ~_PAGE_UNUSED;
if (mm_has_pgste(mm))
ptep_set_pte_at(mm, addr, ptep, entry);
else