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.

Kyle Huey committed 9 years ago

Commit db2336a1 parent bd171175 files · +49 −0Browse files

Unified · Split

5 files

arch/x86/include/asm/kvm_host.h +2 −0
arch/x86/kvm/cpuid.c +3 −0
arch/x86/kvm/cpuid.h +11 −0
arch/x86/kvm/emulate.c +7 −0
arch/x86/kvm/x86.c +26 −0

arch/x86/include/asm/kvm_host.h+2−0

@@ -611,6 +611,8 @@ struct kvm_vcpu_arch { · 610 unmodified lines
611	611	unsigned long dr7;
612	612	unsigned long eff_db[KVM_NR_DB_REGS];
613	613	unsigned long guest_debug_dr7;
	614	+ u64 msr_platform_info;
	615	+ u64 msr_misc_features_enables;
614	616
615	617	u64 mcg_cap;
616	618	u64 mcg_status;

arch/x86/kvm/cpuid.c+3−0

@@ -876,6 +876,9 @@ int kvm_emulate_cpuid(struct kvm_vcpu *vcpu) · 875 unmodified lines
876	876	{
877	877	u32 eax, ebx, ecx, edx;
878	878
	879	+ if (cpuid_fault_enabled(vcpu) && !kvm_require_cpl(vcpu, 0))
	880	+ return 1;
	881	+
879	882	eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
880	883	ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
881	884	kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);

arch/x86/kvm/cpuid.h+11−0

@@ -205,4 +205,15 @@ static inline int guest_cpuid_stepping(struct kvm_vcpu *vcpu) · 204 unmodified lines
205	205	return x86_stepping(best->eax);
206	206	}
207	207
	208	+static inline bool supports_cpuid_fault(struct kvm_vcpu *vcpu)
	209	+{
	210	+ return vcpu->arch.msr_platform_info & MSR_PLATFORM_INFO_CPUID_FAULT;
	211	+}
	212	+
	213	+static inline bool cpuid_fault_enabled(struct kvm_vcpu *vcpu)
	214	+{
	215	+ return vcpu->arch.msr_misc_features_enables &
	216	+ MSR_MISC_FEATURES_ENABLES_CPUID_FAULT;
	217	+}
	218	+
208	219	#endif

arch/x86/kvm/emulate.c+7−0

@@ -3854,6 +3854,13 @@ static int em_sti(struct x86_emulate_ctxt *ctxt) · 3853 unmodified lines
3854	3854	static int em_cpuid(struct x86_emulate_ctxt *ctxt)
3855	3855	{
3856	3856	u32 eax, ebx, ecx, edx;
	3857	+ u64 msr = 0;
	3858	+
	3859	+ ctxt->ops->get_msr(ctxt, MSR_MISC_FEATURES_ENABLES, &msr);
	3860	+ if (msr & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
	3861	+ ctxt->ops->cpl(ctxt)) {
	3862	+ return emulate_gp(ctxt, 0);
	3863	+ }
3857	3864
3858	3865	eax = reg_read(ctxt, VCPU_REGS_RAX);
3859	3866	ecx = reg_read(ctxt, VCPU_REGS_RCX);

arch/x86/kvm/x86.c+26−0

@@ -1007,6 +1007,8 @@ static u32 emulated_msrs[] = { · 1006 unmodified lines
1007	1007	MSR_IA32_MCG_CTL,
1008	1008	MSR_IA32_MCG_EXT_CTL,
1009	1009	MSR_IA32_SMBASE,
	1010	+ MSR_PLATFORM_INFO,
	1011	+ MSR_MISC_FEATURES_ENABLES,
1010	1012	};
1011	1013
1012	1014	static unsigned num_emulated_msrs;
@@ -2314,6 +2316,21 @@ int kvm_set_msr_common(struct kvm_vcpu vcpu, struct msr_data msr_info) · 1301 unmodified lines
2314	2316	return 1;
2315	2317	vcpu->arch.osvw.status = data;
2316	2318	break;
	2319	+ case MSR_PLATFORM_INFO:
	2320	+ if (!msr_info->host_initiated \|\|
	2321	+ data & ~MSR_PLATFORM_INFO_CPUID_FAULT \|\|
	2322	+ (!(data & MSR_PLATFORM_INFO_CPUID_FAULT) &&
	2323	+ cpuid_fault_enabled(vcpu)))
	2324	+ return 1;
	2325	+ vcpu->arch.msr_platform_info = data;
	2326	+ break;
	2327	+ case MSR_MISC_FEATURES_ENABLES:
	2328	+ if (data & ~MSR_MISC_FEATURES_ENABLES_CPUID_FAULT \|\|
	2329	+ (data & MSR_MISC_FEATURES_ENABLES_CPUID_FAULT &&
	2330	+ !supports_cpuid_fault(vcpu)))
	2331	+ return 1;
	2332	+ vcpu->arch.msr_misc_features_enables = data;
	2333	+ break;
2317	2334	default:
2318	2335	if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
2319	2336	return xen_hvm_config(vcpu, data);
@@ -2529,6 +2546,12 @@ int kvm_get_msr_common(struct kvm_vcpu vcpu, struct msr_data msr_info) · 209 unmodified lines
2529	2546	return 1;
2530	2547	msr_info->data = vcpu->arch.osvw.status;
2531	2548	break;
	2549	+ case MSR_PLATFORM_INFO:
	2550	+ msr_info->data = vcpu->arch.msr_platform_info;
	2551	+ break;
	2552	+ case MSR_MISC_FEATURES_ENABLES:
	2553	+ msr_info->data = vcpu->arch.msr_misc_features_enables;
	2554	+ break;
2532	2555	default:
2533	2556	if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
2534	2557	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) · 5175 unmodified lines
7710	7733	if (!init_event) {
7711	7734	kvm_pmu_reset(vcpu);
7712	7735	vcpu->arch.smbase = 0x30000;
	7736	+
	7737	+ vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
	7738	+ vcpu->arch.msr_misc_features_enables = 0;
7713	7739	}
7714	7740
7715	7741	memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));