x86/kvm/hyper-v: Introduce nested_get_evmcs_version() helper

The upcoming KVM_GET_SUPPORTED_HV_CPUID ioctl will need to return
Enlightened VMCS version in HYPERV_CPUID_NESTED_FEATURES.EAX when
it was enabled.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3cbe67a..0762e81 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -7047,6 +7047,12 @@ static int svm_unregister_enc_region(struct kvm *kvm,
 	return ret;
 }
 
+static uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu)
+{
+	/* Not supported */
+	return 0;
+}
+
 static int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 				   uint16_t *vmcs_version)
 {
@@ -7185,6 +7191,7 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
 	.mem_enc_unreg_region = svm_unregister_enc_region,
 
 	.nested_enable_evmcs = nested_enable_evmcs,
+	.nested_get_evmcs_version = nested_get_evmcs_version,
 };
 
 static int __init svm_init(void)