linux-kernel - [PATCH 4.6 079/203] KVM: s390/mm: Fix CMMA reset during reboot

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Date:	Mon, 25 Jul 2016 13:54:54 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: [PATCH 4.6 079/203] KVM: s390/mm: Fix CMMA reset during reboot

4.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Christian Borntraeger <borntraeger@...ibm.com>

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)

Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
Fixes: 1e133ab296f ("s390/mm: split arch/s390/mm/pgtable.c")
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -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));