[PATCH v2 1/2] KVM: s390: fix ESSA addressing exception injection in migration mode

[Gautam Gala <ggala@linux.ibm.com>]

__do_essa() treated any negative return from dat_perform_essa() as the
normal "no CBRL entry appended" case and returned 0, so a page-table
walk failure silently dropped the addressing exception.

Return -PGM_ADDRESSING on a walk failure and inject the program
interrupt in __do_essa() for the -PGM_ADDRESSING return value.

DAT_WALK_ANY is required in the dat_entry_walk() call so that a GFN
backed by a large page (segment or region entry) does not return an
error: the walk stops early but succeeds, leaving ptep as NULL, which is
already handled by the existing "set exception state, return -1" path.
Without DAT_WALK_ANY such addresses would fall through to the new error
path and incorrectly inject PGM_ADDRESSING.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Reported-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Suggested-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Gautam Gala <ggala@linux.ibm.com>
---
 arch/s390/kvm/gmap/dat.c  | 5 ++++-
 arch/s390/kvm/s390/priv.c | 2 ++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/s390/kvm/gmap/dat.c b/arch/s390/kvm/gmap/dat.c
index ff80d02c9f56..a2031aece4ed 100644
--- a/arch/s390/kvm/gmap/dat.c
+++ b/arch/s390/kvm/gmap/dat.c
@@ -1084,6 +1084,7 @@ int dat_set_prefix_notif_bit(union asce asce, gfn_t gfn)
  * * %1 if the page state has been altered and the page is to be added to the CBRL
  * * %0 if the page state has been altered, but the page is not to be added to the CBRL
  * * %-1 if the page state has not been altered and the page is not to be added to the CBRL
+ * * %PGM_ADDRESSING if the guest page-table walk failed
  */
 int dat_perform_essa(union asce asce, gfn_t gfn, int orc, union essa_state *state, bool *dirty)
 {
@@ -1092,7 +1093,9 @@ int dat_perform_essa(union asce asce, gfn_t gfn, int orc, union essa_state *stat
 	union pte *ptep;
 	int res = 0;
 
-	if (dat_entry_walk(NULL, gfn, asce, 0, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep)) {
+	if (dat_entry_walk(NULL, gfn, asce, DAT_WALK_ANY, TABLE_TYPE_PAGE_TABLE, &crstep, &ptep))
+		return PGM_ADDRESSING;
+	if (!ptep) {
 		*state = (union essa_state) { .exception = 1 };
 		return -1;
 	}
diff --git a/arch/s390/kvm/s390/priv.c b/arch/s390/kvm/s390/priv.c
index b3cb2c2c3aa7..9089b8f5d550 100644
--- a/arch/s390/kvm/s390/priv.c
+++ b/arch/s390/kvm/s390/priv.c
@@ -1168,6 +1168,8 @@ static inline int __do_essa(struct kvm_vcpu *vcpu, const int orc)
 	entries = (vcpu->arch.sie_block->cbrlo & ~PAGE_MASK) >> 3;
 
 	nappended = dat_perform_essa(vcpu->arch.gmap->asce, gfn, orc, &state, &dirtied);
+	if (nappended == PGM_ADDRESSING)
+		return kvm_s390_inject_program_int(vcpu, PGM_ADDRESSING);
 	vcpu->run->s.regs.gprs[r1] = state.val;
 	if (nappended < 0)
 		return 0;
-- 
2.55.0