Patch "KVM: s390/mm: Fix CMMA reset during reboot" has been added to the 4.6-stable tree

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

KVM: s390/mm: Fix CMMA reset during reboot

to the 4.6-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:
kvm-s390-mm-fix-cmma-reset-during-reboot.patch
and it can be found in the queue-4.6 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: Mon, 13 Jun 2016 13:14:56 +0200
Subject: KVM: s390/mm: Fix CMMA reset during reboot

From: Christian Borntraeger <[email protected]>

commit 1c343f7b0e177e8ca7f4d4a5dd1fa790f85abbcc upstream.

commit 1e133ab296f ("s390/mm: split arch/s390/mm/pgtable.c") factored out the page table handling code from __gmap_zap and __s390_reset_cmma into ptep_zap_unused and added a simple flag that tells which one of the function (reset or not) is to be made. This also changed the behaviour, as it also zaps unused page table entries on reset.
Turns out that this is wrong as s390_reset_cmma uses the page walker, which DOES NOT take the ptl lock.

The most simple fix is to not do the zapping part on reset (which uses the walker)

---
 arch/s390/mm/pgtable.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -437,7 +437,7 @@ void ptep_zap_unused(struct mm_struct *m
 	pgste = pgste_get_lock(ptep);
 	pgstev = pgste_val(pgste);
 	pte = *ptep;
-	if (pte_swap(pte) &&
+	if (!reset && pte_swap(pte) &&
 	    ((pgstev & _PGSTE_GPS_USAGE_MASK) == _PGSTE_GPS_USAGE_UNUSED ||
 	     (pgstev & _PGSTE_GPS_ZERO))) {
 		ptep_zap_swap_entry(mm, pte_to_swp_entry(pte));

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

queue-4.6/kvm-s390-mm-fix-cmma-reset-during-reboot.patch