[PATCH v1 6/7] KVM: s390: vsie: Fix off-by-one when protecting guest page tables

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

When shadowing, the guest page tables are write-protected, in order to
trap changes and properly unshadow the shadow mapping for the nested
guest. Already shadowed levels are skipped, so that only the needed
levels are write protected.

Currently the levels that get write protected are exactly one level too
deep: the last level (nested guest memory) gets protected in the wrong
way, and will be protected again correctly a few lines afterwards; most
importantly, the highest non-shadowed level does *not* get write
protected.

This leads to all sorts of races and other issues.

Write protect the correct levels, so that all the levels that need to
be protected are protected, and avoid double protecting the last level.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
---
 arch/s390/kvm/gaccess.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 3bcf988d6faa..8b287fcf611d 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -1516,8 +1516,8 @@ static int _gaccess_do_shadow(struct kvm_s390_mmu_cache *mc, struct gmap *sg,
 	 * only the page containing the entry, not the whole table.
 	 */
 	for (i = gl ; i >= w->level; i--) {
-		rc = gmap_protect_rmap(mc, sg, entries[i - 1].gfn, gpa_to_gfn(saddr),
-				       entries[i - 1].pfn, i, entries[i - 1].writable);
+		rc = gmap_protect_rmap(mc, sg, entries[i].gfn, gpa_to_gfn(saddr),
+				       entries[i].pfn, i + 1, entries[i].writable);
 		if (rc)
 			return rc;
 		if (!sg->parent)
-- 
2.53.0