KVM: nSVM: Use KVM-governed feature framework to track "TSC scaling enabled"

Track "TSC scaling exposed to L1" via a governed feature flag instead of
using a dedicated bit/flag in vcpu_svm.

Note, this fixes a benign bug where KVM would mark TSC scaling as exposed
to L1 even if overall nested SVM supported is disabled, i.e. KVM would let
L1 write MSR_AMD64_TSC_RATIO even when KVM didn't advertise TSCRATEMSR
support to userspace.

Reviewed-by: Yuan Yao <yuan.yao@intel.com>
Link: https://lore.kernel.org/r/20230815203653.519297-10-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/governed_features.h

@@ -9,6 +9,7 @@ KVM_GOVERNED_X86_FEATURE(GBPAGES)
 KVM_GOVERNED_X86_FEATURE(XSAVES)
 KVM_GOVERNED_X86_FEATURE(VMX)
 KVM_GOVERNED_X86_FEATURE(NRIPS)
+KVM_GOVERNED_X86_FEATURE(TSCRATEMSR)
 
 #undef KVM_GOVERNED_X86_FEATURE
 #undef KVM_GOVERNED_FEATURE

arch/x86/kvm/svm/nested.c

@@ -695,7 +695,7 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
 
 	vmcb02->control.tsc_offset = vcpu->arch.tsc_offset;
 
-	if (svm->tsc_scaling_enabled &&
+	if (guest_can_use(vcpu, X86_FEATURE_TSCRATEMSR) &&
 	    svm->tsc_ratio_msr != kvm_caps.default_tsc_scaling_ratio)
 		nested_svm_update_tsc_ratio_msr(vcpu);
 

arch/x86/kvm/svm/svm.c

@@ -2795,7 +2795,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 
 	switch (msr_info->index) {
 	case MSR_AMD64_TSC_RATIO:
-		if (!msr_info->host_initiated && !svm->tsc_scaling_enabled)
+		if (!msr_info->host_initiated &&
+		    !guest_can_use(vcpu, X86_FEATURE_TSCRATEMSR))
 			return 1;
 		msr_info->data = svm->tsc_ratio_msr;
 		break;
@@ -2937,7 +2938,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 	switch (ecx) {
 	case MSR_AMD64_TSC_RATIO:
 
-		if (!svm->tsc_scaling_enabled) {
+		if (!guest_can_use(vcpu, X86_FEATURE_TSCRATEMSR)) {
 
 			if (!msr->host_initiated)
 				return 1;
@@ -2959,7 +2960,8 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 
 		svm->tsc_ratio_msr = data;
 
-		if (svm->tsc_scaling_enabled && is_guest_mode(vcpu))
+		if (guest_can_use(vcpu, X86_FEATURE_TSCRATEMSR) &&
+		    is_guest_mode(vcpu))
 			nested_svm_update_tsc_ratio_msr(vcpu);
 
 		break;
@@ -4260,8 +4262,8 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 		kvm_governed_feature_set(vcpu, X86_FEATURE_XSAVES);
 
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_NRIPS);
+	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_TSCRATEMSR);
 
-	svm->tsc_scaling_enabled = tsc_scaling && guest_cpuid_has(vcpu, X86_FEATURE_TSCRATEMSR);
 	svm->lbrv_enabled = lbrv && guest_cpuid_has(vcpu, X86_FEATURE_LBRV);
 
 	svm->v_vmload_vmsave_enabled = vls && guest_cpuid_has(vcpu, X86_FEATURE_V_VMSAVE_VMLOAD);

arch/x86/kvm/svm/svm.h

@@ -259,7 +259,6 @@ struct vcpu_svm {
 	bool soft_int_injected;
 
 	/* optional nested SVM features that are enabled for this guest  */
-	bool tsc_scaling_enabled          : 1;
 	bool v_vmload_vmsave_enabled      : 1;
 	bool lbrv_enabled                 : 1;
 	bool pause_filter_enabled         : 1;