[PATCH v3 8/8] KVM: s390: Fix race in _destroy_pages_crste()

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

Use READ_ONCE() in _destroy_pages_crste() to read the crste, avoid
dereferencing the pointer multiple times.

Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/gmap/gmap.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/gmap/gmap.c b/arch/s390/kvm/gmap/gmap.c
index 4968330e9553..3f3fa864cc36 100644
--- a/arch/s390/kvm/gmap/gmap.c
+++ b/arch/s390/kvm/gmap/gmap.c
@@ -994,11 +994,13 @@ static long _destroy_pages_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct da
 static long _destroy_pages_crste(union crste *crstep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
 {
 	phys_addr_t origin, cur, end;
+	union crste crste;
 
-	if (!crstep->h.fc || !crstep->s.fc1.pr)
+	crste = READ_ONCE(*crstep);
+	if (!crste.h.fc || !crste.s.fc1.pr)
 		return 0;
 
-	origin = crste_origin_large(*crstep);
+	origin = crste_origin_large(crste);
 	cur = ((max(gfn, walk->start) - gfn) << PAGE_SHIFT) + origin;
 	end = ((min(next, walk->end) - gfn) << PAGE_SHIFT) + origin;
 	for ( ; cur < end; cur += PAGE_SIZE)
-- 
2.55.0