[PATCH v2 1/5] KVM: s390: vsie: Fix region 1 ASCE sanity shadow address checks

[David Hildenbrand]

In case we have a region 1 ASCE, our shadow/g3 address can have any value.
Unfortunately, (-1UL << 64) is undefined and triggers sometimes,
rejecting valid shadow addresses when trying to walk our shadow table
hierarchy.

The result is that the prefix cannot get mapped and will loop basically
forever trying to map it (-EAGAIN loop).

After all, the broken check is only a sanity check, our table shadowing
code in kvm_s390_shadow_tables() already checks these conditions, injecting
proper translation exceptions. Turn it into a WARN_ON_ONCE().

Fixes: 4be130a08420 ("s390/mm: add shadow gmap support")
Tested-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Reported-by: Janosch Frank <frankja@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v4.8+
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
 arch/s390/mm/gmap.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 2fbece47ef6f..b93dd54b234a 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -787,14 +787,18 @@ static void gmap_call_notifier(struct gmap *gmap, unsigned long start,
 static inline unsigned long *gmap_table_walk(struct gmap *gmap,
 					     unsigned long gaddr, int level)
 {
+	const int asce_type = gmap->asce & _ASCE_TYPE_MASK;
 	unsigned long *table;
 
 	if ((gmap->asce & _ASCE_TYPE_MASK) + 4 < (level * 4))
 		return NULL;
 	if (gmap_is_shadow(gmap) && gmap->removed)
 		return NULL;
-	if (gaddr & (-1UL << (31 + ((gmap->asce & _ASCE_TYPE_MASK) >> 2)*11)))
+
+	if (WARN_ON_ONCE(asce_type != _ASCE_TYPE_REGION1 &&
+			 gaddr & (-1UL << (31 + (asce_type >> 2) * 11))))
 		return NULL;
+
 	table = gmap->table;
 	switch (gmap->asce & _ASCE_TYPE_MASK) {
 	case _ASCE_TYPE_REGION1:
-- 
2.25.1