KVM: arm64: pvtime: steal-time is only supported when configured

Don't confuse the guest by saying steal-time is supported when
it hasn't been configured by userspace and won't work.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200804170604.42662-2-drjones@redhat.com

arch/arm64/kvm/pvtime.c

@@ -43,7 +43,8 @@ long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu)
 	switch (feature) {
 	case ARM_SMCCC_HV_PV_TIME_FEATURES:
 	case ARM_SMCCC_HV_PV_TIME_ST:
-		val = SMCCC_RET_SUCCESS;
+		if (vcpu->arch.steal.base != GPA_INVALID)
+			val = SMCCC_RET_SUCCESS;
 		break;
 	}