arm64: KVM: Inject a vSerror if detecting a bad GICV access at EL2

If, when proxying a GICV access at EL2, we detect that the guest is
doing something silly, report an EL1 SError instead ofgnoring the
access.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 8b81cc6..731519c 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -311,9 +311,21 @@
 			!kvm_vcpu_dabt_isextabt(vcpu) &&
 			!kvm_vcpu_dabt_iss1tw(vcpu);
 
-		if (valid && __vgic_v2_perform_cpuif_access(vcpu)) {
-			__skip_instr(vcpu);
-			goto again;
+		if (valid) {
+			int ret = __vgic_v2_perform_cpuif_access(vcpu);
+
+			if (ret == 1) {
+				__skip_instr(vcpu);
+				goto again;
+			}
+
+			if (ret == -1) {
+				/* Promote an illegal access to an SError */
+				__skip_instr(vcpu);
+				exit_code = ARM_EXCEPTION_EL1_SERROR;
+			}
+
+			/* 0 falls through to be handler out of EL2 */
 		}
 	}