KVM: x86: hyper-v: Cache guest CPUID leaves determining features availability

Limiting exposed Hyper-V features requires a fast way to check if the
particular feature is exposed in guest visible CPUIDs or not. To aboid
looping through all CPUID entries on every hypercall/MSR access cache
the required leaves on CPUID update.
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20210521095204.2161214-4-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -544,6 +544,14 @@ struct kvm_vcpu_hv {
 	DECLARE_BITMAP(stimer_pending_bitmap, HV_SYNIC_STIMER_COUNT);
 	cpumask_t tlb_flush;
 	bool enforce_cpuid;
+	struct {
+		u32 features_eax; /* HYPERV_CPUID_FEATURES.EAX */
+		u32 features_ebx; /* HYPERV_CPUID_FEATURES.EBX */
+		u32 features_edx; /* HYPERV_CPUID_FEATURES.EDX */
+		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 */
+	} cpuid_cache;
 };
 
 /* Xen HVM per vcpu emulation context */

arch/x86/kvm/hyperv.c

@@ -274,15 +274,10 @@ static int synic_set_msr(struct kvm_vcpu_hv_synic *synic,
 
 static bool kvm_hv_is_syndbg_enabled(struct kvm_vcpu *vcpu)
 {
-	struct kvm_cpuid_entry2 *entry;
-
-	entry = kvm_find_cpuid_entry(vcpu,
-				     HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES,
-				     0);
-	if (!entry)
-		return false;
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 
-	return entry->eax & HV_X64_SYNDBG_CAP_ALLOW_KERNEL_DEBUGGING;
+	return hv_vcpu->cpuid_cache.syndbg_cap_eax &
+		HV_X64_SYNDBG_CAP_ALLOW_KERNEL_DEBUGGING;
 }
 
 static int kvm_hv_syndbg_complete_userspace(struct kvm_vcpu *vcpu)
@@ -1845,12 +1840,46 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpuid_entry2 *entry;
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
 
 	entry = kvm_find_cpuid_entry(vcpu, HYPERV_CPUID_INTERFACE, 0);
-	if (entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX)
+	if (entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX) {
 		vcpu->arch.hyperv_enabled = true;
-	else
+	} else {
 		vcpu->arch.hyperv_enabled = false;
+		return;
+	}
+
+	if (!to_hv_vcpu(vcpu) && kvm_hv_vcpu_init(vcpu))
+		return;
+
+	hv_vcpu = to_hv_vcpu(vcpu);
+
+	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;
 }
 
 int kvm_hv_set_enforce_cpuid(struct kvm_vcpu *vcpu, bool enforce)