KVM: x86: virtualize cpuid faulting

Hardware support for faulting on the cpuid instruction is not required to
emulate it, because cpuid triggers a VM exit anyways. KVM handles the relevant
MSRs (MSR_PLATFORM_INFO and MSR_MISC_FEATURES_ENABLE) and upon a
cpuid-induced VM exit checks the cpuid faulting state and the CPL.
kvm_require_cpl is even kind enough to inject the GP fault for us.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Reviewed-by: David Matlack <dmatlack@google.com>
[Return "1" from kvm_emulate_cpuid, it's not void. - Paolo]
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 2cc5ec7cc6f55d67e2483f8e1f3f4c89bdba1990..f5c942edbc86c050ca595aa450b3a254c15f2233 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -611,6 +611,8 @@ struct kvm_vcpu_arch {
        unsigned long dr7;
        unsigned long eff_db[KVM_NR_DB_REGS];
        unsigned long guest_debug_dr7;
+       u64 msr_platform_info;
+       u64 msr_misc_features_enables;
 
        u64 mcg_cap;
        u64 mcg_status;

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index efde6cc50875184bd51e86ba08116a6095dd070b..a181ae76c71ce102f88f6a4ee9cc3233677c55e2 100644 (file)
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -876,6 +876,9 @@ int kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
 {
        u32 eax, ebx, ecx, edx;
 
+       if (cpuid_fault_enabled(vcpu) && !kvm_require_cpl(vcpu, 0))
+               return 1;
+
        eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
        ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
        kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 35058c2c0eeabe0fd9dedd45999478d5cb61fabb..a6fd40aade7cbf9e798591382c2382267d3141fc 100644 (file)
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -205,4 +205,15 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu)
        return x86_stepping(best->eax);
 }
 
+static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
+{
+       return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;
+}
+
+static inline bool cpuid_fault_enabled(struct kvm_vcpu *vcpu)
+{
+       return vcpu->arch.msr_misc_features_enables &
+                 MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
+}
+
 #endif

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 45c7306c8780b23494f22d8a775f1486ea29eafc..6a2ea945d01f124c0ecd254bf29d047908bb8167 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3854,6 +3854,13 @@ static int em_sti(struct x86_emulate_ctxt *ctxt)
 static int em_cpuid(struct x86_emulate_ctxt *ctxt)
 {
        u32 eax, ebx, ecx, edx;
+       u64 msr = 0;
+
+       ctxt->ops->get_msr(ctxt, MSR_MISC_FEATURES_ENABLES, &msr);
+       if (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
+           ctxt->ops->cpl(ctxt)) {
+               return emulate_gp(ctxt, 0);
+       }
 
        eax = reg_read(ctxt, VCPU_REGS_RAX);
        ecx = reg_read(ctxt, VCPU_REGS_RCX);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 34bf64fb4dea827fb34acc09f4047d5ad3b8945c..49a69c0a0d50777cd2c9dbb116b71f9334da838c 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1007,6 +1007,8 @@ static u32 emulated_msrs[] = {
        MSR_IA32_MCG_CTL,
        MSR_IA32_MCG_EXT_CTL,
        MSR_IA32_SMBASE,
+       MSR_PLATFORM_INFO,
+       MSR_MISC_FEATURES_ENABLES,
 };
 
 static unsigned num_emulated_msrs;
@@ -2314,6 +2316,21 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                        return 1;
                vcpu->arch.osvw.status = data;
                break;
+       case MSR_PLATFORM_INFO:
+               if (!msr_info->host_initiated ||
+                   data & ~MSR_PLATFORM_INFO_CPUID_FAULT ||
+                   (!(data & MSR_PLATFORM_INFO_CPUID_FAULT) &&
+                    cpuid_fault_enabled(vcpu)))
+                       return 1;
+               vcpu->arch.msr_platform_info = data;
+               break;
+       case MSR_MISC_FEATURES_ENABLES:
+               if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT ||
+                   (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
+                    !supports_cpuid_fault(vcpu)))
+                       return 1;
+               vcpu->arch.msr_misc_features_enables = data;
+               break;
        default:
                if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
                        return xen_hvm_config(vcpu, data);
@@ -2529,6 +2546,12 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                        return 1;
                msr_info->data = vcpu->arch.osvw.status;
                break;
+       case MSR_PLATFORM_INFO:
+               msr_info->data = vcpu->arch.msr_platform_info;
+               break;
+       case MSR_MISC_FEATURES_ENABLES:
+               msr_info->data = vcpu->arch.msr_misc_features_enables;
+               break;
        default:
                if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
                        return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
@@ -7710,6 +7733,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
        if (!init_event) {
                kvm_pmu_reset(vcpu);
                vcpu->arch.smbase = 0x30000;
+
+               vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
+               vcpu->arch.msr_misc_features_enables = 0;
        }
 
        memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));