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: NVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1186,6 +1186,7 @@ struct kvm_x86_ops {
 
 	int (*nested_enable_evmcs)(struct kvm_vcpu *vcpu,
 				   uint16_t *vmcs_version);
+	uint16_t (*nested_get_evmcs_version)(struct kvm_vcpu *vcpu);
 };
 
 struct kvm_arch_async_pf {

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)

arch/x86/kvm/vmx/evmcs.c

@@ -313,19 +313,28 @@ void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf)
 }
 #endif
 
+uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu)
+{
+       struct vcpu_vmx *vmx = to_vmx(vcpu);
+       /*
+        * vmcs_version represents the range of supported Enlightened VMCS
+        * versions: lower 8 bits is the minimal version, higher 8 bits is the
+        * maximum supported version. KVM supports versions from 1 to
+        * KVM_EVMCS_VERSION.
+        */
+       if (vmx->nested.enlightened_vmcs_enabled)
+               return (KVM_EVMCS_VERSION << 8) | 1;
+
+       return 0;
+}
+
 int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 			uint16_t *vmcs_version)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 
-	/*
-	 * vmcs_version represents the range of supported Enlightened VMCS
-	 * versions: lower 8 bits is the minimal version, higher 8 bits is the
-	 * maximum supported version. KVM supports versions from 1 to
-	 * KVM_EVMCS_VERSION.
-	 */
 	if (vmcs_version)
-		*vmcs_version = (KVM_EVMCS_VERSION << 8) | 1;
+		*vmcs_version = nested_get_evmcs_version(vcpu);
 
 	/* We don't support disabling the feature for simplicity. */
 	if (vmx->nested.enlightened_vmcs_enabled)

arch/x86/kvm/vmx/evmcs.h

@@ -195,6 +195,7 @@ static inline void evmcs_sanitize_exec_ctrls(struct vmcs_config *vmcs_conf) {}
 static inline void evmcs_touch_msr_bitmap(void) {}
 #endif /* IS_ENABLED(CONFIG_HYPERV) */
 
+uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu);
 int nested_enable_evmcs(struct kvm_vcpu *vcpu,
 			uint16_t *vmcs_version);
 

arch/x86/kvm/vmx/nested.c

@@ -5669,6 +5669,7 @@ __init int nested_vmx_hardware_setup(int (*exit_handlers[])(struct kvm_vcpu *))
 	kvm_x86_ops->set_nested_state = vmx_set_nested_state;
 	kvm_x86_ops->get_vmcs12_pages = nested_get_vmcs12_pages,
 	kvm_x86_ops->nested_enable_evmcs = nested_enable_evmcs;
+	kvm_x86_ops->nested_get_evmcs_version = nested_get_evmcs_version;
 
 	return 0;
 }