Patch "s390/mm: fix CMMA vs KSM vs others" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

s390/mm: fix CMMA vs KSM vs others

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:

     s390-mm-fix-cmma-vs-ksm-vs-others.patch

and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Christian Borntraeger <[email protected]>
Date: Sun, 9 Apr 2017 22:09:38 +0200
Subject: s390/mm: fix CMMA vs KSM vs others

From: Christian Borntraeger <[email protected]>

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.

---
 arch/s390/include/asm/pgtable.h |    2 ++
 1 file changed, 2 insertions(+)

@@ -1029,6 +1029,8 @@ int get_guest_storage_key(struct mm_stru
 static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 			      pte_t *ptep, pte_t entry)
 {
+	if (pte_present(entry))
+		pte_val(entry) &= ~_PAGE_UNUSED;
 	if (mm_has_pgste(mm))
 		ptep_set_pte_at(mm, addr, ptep, entry);
 	else

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/s390-mm-fix-cmma-vs-ksm-vs-others.patch