KVM: arm64: Don't skip cache maintenance for read-only memslots

If a guest performs cache maintenance on a read-only memslot, we should
inform userspace rather than skip the instruction altogether.
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20200729102821.23392-4-will@kernel.org

arch/arm64/kvm/mmu.c

@@ -2121,7 +2121,7 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		 * So let's assume that the guest is just being
 		 * cautious, and skip the instruction.
 		 */
-		if (kvm_vcpu_dabt_is_cm(vcpu)) {
+		if (kvm_is_error_hva(hva) && kvm_vcpu_dabt_is_cm(vcpu)) {
 			kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu));
 			ret = 1;
 			goto out_unlock;