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

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

Note, checking KVM's capabilities instead of the "vgif" param means that
the code isn't strictly equivalent, as vgif_enabled could have been set
if nested=false where as that the governed feature cannot.  But that's a
glorified nop as the feature/flag is consumed only by paths that are

Link: https://lore.kernel.org/r/20230815203653.519297-14-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

arch/x86/kvm/governed_features.h

@@ -14,6 +14,7 @@ KVM_GOVERNED_X86_FEATURE(V_VMSAVE_VMLOAD)
 KVM_GOVERNED_X86_FEATURE(LBRV)
 KVM_GOVERNED_X86_FEATURE(PAUSEFILTER)
 KVM_GOVERNED_X86_FEATURE(PFTHRESHOLD)
+KVM_GOVERNED_X86_FEATURE(VGIF)
 
 #undef KVM_GOVERNED_X86_FEATURE
 #undef KVM_GOVERNED_FEATURE

arch/x86/kvm/svm/nested.c

@@ -660,7 +660,8 @@ static void nested_vmcb02_prepare_control(struct vcpu_svm *svm,
 	 * exit_int_info, exit_int_info_err, next_rip, insn_len, insn_bytes.
 	 */
 
-	if (svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK))
+	if (guest_can_use(vcpu, X86_FEATURE_VGIF) &&
+	    (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK))
 		int_ctl_vmcb12_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);
 	else
 		int_ctl_vmcb01_bits |= (V_GIF_MASK | V_GIF_ENABLE_MASK);

arch/x86/kvm/svm/svm.c

@@ -4273,8 +4273,7 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_PAUSEFILTER);
 	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_PFTHRESHOLD);
-
-	svm->vgif_enabled = vgif && guest_cpuid_has(vcpu, X86_FEATURE_VGIF);
+	kvm_governed_feature_check_and_set(vcpu, X86_FEATURE_VGIF);
 
 	svm->vnmi_enabled = vnmi && guest_cpuid_has(vcpu, X86_FEATURE_VNMI);
 

arch/x86/kvm/svm/svm.h

@@ -22,6 +22,7 @@
 #include <asm/svm.h>
 #include <asm/sev-common.h>
 
+#include "cpuid.h"
 #include "kvm_cache_regs.h"
 
 #define __sme_page_pa(x) __sme_set(page_to_pfn(x) << PAGE_SHIFT)
@@ -259,7 +260,6 @@ struct vcpu_svm {
 	bool soft_int_injected;
 
 	/* optional nested SVM features that are enabled for this guest  */
-	bool vgif_enabled                 : 1;
 	bool vnmi_enabled                 : 1;
 
 	u32 ldr_reg;
@@ -485,7 +485,8 @@ static inline bool svm_is_intercept(struct vcpu_svm *svm, int bit)
 
 static inline bool nested_vgif_enabled(struct vcpu_svm *svm)
 {
-	return svm->vgif_enabled && (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK);
+	return guest_can_use(&svm->vcpu, X86_FEATURE_VGIF) &&
+	       (svm->nested.ctl.int_ctl & V_GIF_ENABLE_MASK);
 }
 
 static inline struct vmcb *get_vgif_vmcb(struct vcpu_svm *svm)