KVM: x86: hyper-v: Cache HYPERV_CPUID_NESTED_FEATURES CPUID leaf

KVM has to check guest visible HYPERV_CPUID_NESTED_FEATURES.EBX CPUID
leaf to know which Enlightened VMCS definition to use (original or 2022
update). Cache the leaf along with other Hyper-V CPUID feature leaves
to make the check quick.
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220830133737.1539624-12-vkuznets@redhat.comSigned-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -615,6 +615,8 @@ struct kvm_vcpu_hv {
 		u32 enlightenments_eax; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EAX */
 		u32 enlightenments_ebx; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EBX */
 		u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
+		u32 nested_eax; /* HYPERV_CPUID_NESTED_FEATURES.EAX */
+		u32 nested_ebx; /* HYPERV_CPUID_NESTED_FEATURES.EBX */
 	} cpuid_cache;
 };
 

arch/x86/kvm/hyperv.c

@@ -2018,6 +2018,12 @@ void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu, bool hyperv_enabled)
 	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES);
 	if (entry)
 		hv_vcpu->cpuid_cache.syndbg_cap_eax = entry->eax;
+
+	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_NESTED_FEATURES);
+	if (entry) {
+		hv_vcpu->cpuid_cache.nested_eax = entry->eax;
+		hv_vcpu->cpuid_cache.nested_ebx = entry->ebx;
+	}
 }
 
 int kvm_hv_set_enforce_cpuid(struct kvm_vcpu *vcpu, bool enforce)