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>

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 556a8ec..95b254b 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/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 */

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 02b0ee1..7e7928f 100644 (file)
--- a/arch/x86/kvm/hyperv.c
+++ b/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 @@ ret_success:
 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)