[PATCH v4 06/25] KVM: x86: hyper-v: Cache HYPERV_CPUID_NESTED_FEATURES CPUID leaf

[Vitaly Kuznetsov <vkuznets@redhat.com>]

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.

While on it, wipe the whole 'hv_vcpu->cpuid_cache' with memset() instead
of having to zero each particular member when the corresponding CPUID entry
was not found.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/hyperv.c           | 17 ++++++++---------
 2 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index de5a149d0971..077ec9cf3169 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -616,6 +616,8 @@ 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;
 };
 
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index e08189211d9a..a8e4944ca110 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2005,31 +2005,30 @@ void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
 
 	hv_vcpu = to_hv_vcpu(vcpu);
 
+	memset(&hv_vcpu->cpuid_cache, 0, sizeof(hv_vcpu->cpuid_cache));
+
 	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_FEATURES, 0);
 	if (entry) {
 		hv_vcpu->cpuid_cache.features_eax = entry->eax;
 		hv_vcpu->cpuid_cache.features_ebx = entry->ebx;
 		hv_vcpu->cpuid_cache.features_edx = entry->edx;
-	} else {
-		hv_vcpu->cpuid_cache.features_eax = 0;
-		hv_vcpu->cpuid_cache.features_ebx = 0;
-		hv_vcpu->cpuid_cache.features_edx = 0;
 	}
 
 	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_ENLIGHTMENT_INFO, 0);
 	if (entry) {
 		hv_vcpu->cpuid_cache.enlightenments_eax = entry->eax;
 		hv_vcpu->cpuid_cache.enlightenments_ebx = entry->ebx;
-	} else {
-		hv_vcpu->cpuid_cache.enlightenments_eax = 0;
-		hv_vcpu->cpuid_cache.enlightenments_ebx = 0;
 	}
 
 	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES, 0);
 	if (entry)
 		hv_vcpu->cpuid_cache.syndbg_cap_eax = entry->eax;
-	else
-		hv_vcpu->cpuid_cache.syndbg_cap_eax = 0;
+
+	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_NESTED_FEATURES, 0);
+	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)
-- 
2.35.3