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Subject[PATCH v9 7/7] KVM: x86: virtualize cpuid faulting
Date
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>
---
arch/x86/include/asm/kvm_host.h | 2 ++
arch/x86/kvm/cpuid.c | 3 +++
arch/x86/kvm/x86.c | 28 ++++++++++++++++++++++++++++
3 files changed, 33 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index bdde807..5edef7b 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -592,16 +592,18 @@ struct kvm_vcpu_arch {
u64 pat;

unsigned switch_db_regs;
unsigned long db[KVM_NR_DB_REGS];
unsigned long dr6;
unsigned long dr7;
unsigned long eff_db[KVM_NR_DB_REGS];
unsigned long guest_debug_dr7;
+ bool cpuid_fault_supported;
+ bool cpuid_fault;

u64 mcg_cap;
u64 mcg_status;
u64 mcg_ctl;
u64 mcg_ext_ctl;
u64 *mce_banks;

/* Cache MMIO info */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index afa7bbb..ed8436a 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -862,16 +862,19 @@ void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx);
}
EXPORT_SYMBOL_GPL(kvm_cpuid);

void kvm_emulate_cpuid(struct kvm_vcpu *vcpu)
{
u32 function, eax, ebx, ecx, edx;

+ if (vcpu->arch.cpuid_fault && !kvm_require_cpl(vcpu, 0))
+ return;
+
function = eax = kvm_register_read(vcpu, VCPU_REGS_RAX);
ecx = kvm_register_read(vcpu, VCPU_REGS_RCX);
kvm_cpuid(vcpu, &eax, &ebx, &ecx, &edx);
kvm_register_write(vcpu, VCPU_REGS_RAX, eax);
kvm_register_write(vcpu, VCPU_REGS_RBX, ebx);
kvm_register_write(vcpu, VCPU_REGS_RCX, ecx);
kvm_register_write(vcpu, VCPU_REGS_RDX, edx);
kvm_x86_ops->skip_emulated_instruction(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3017de0..9cd6462 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -986,16 +986,18 @@ static u32 emulated_msrs[] = {

MSR_IA32_TSC_ADJUST,
MSR_IA32_TSCDEADLINE,
MSR_IA32_MISC_ENABLE,
MSR_IA32_MCG_STATUS,
MSR_IA32_MCG_CTL,
MSR_IA32_MCG_EXT_CTL,
MSR_IA32_SMBASE,
+ MSR_PLATFORM_INFO,
+ MSR_MISC_FEATURES_ENABLES,
};

static unsigned num_emulated_msrs;

bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer)
{
if (efer & efer_reserved_bits)
return false;
@@ -2269,16 +2271,29 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
vcpu->arch.osvw.length = data;
break;
case MSR_AMD64_OSVW_STATUS:
if (!guest_cpuid_has_osvw(vcpu))
return 1;
vcpu->arch.osvw.status = data;
break;
+ case MSR_PLATFORM_INFO:
+ if (!msr_info->host_initiated ||
+ data & ~PLATINFO_CPUID_FAULT ||
+ (!!(data & PLATINFO_CPUID_FAULT) && vcpu->arch.cpuid_fault))
+ return 1;
+ vcpu->arch.cpuid_fault_supported = !!(data & PLATINFO_CPUID_FAULT);
+ break;
+ case MSR_MISC_FEATURES_ENABLES:
+ if (data & ~CPUID_FAULT_ENABLE ||
+ !vcpu->arch.cpuid_fault_supported)
+ return 1;
+ vcpu->arch.cpuid_fault = !!(data & CPUID_FAULT_ENABLE);
+ break;
default:
if (msr && (msr == vcpu->kvm->arch.xen_hvm_config.msr))
return xen_hvm_config(vcpu, data);
if (kvm_pmu_is_valid_msr(vcpu, msr))
return kvm_pmu_set_msr(vcpu, msr_info);
if (!ignore_msrs) {
vcpu_unimpl(vcpu, "unhandled wrmsr: 0x%x data 0x%llx\n",
msr, data);
@@ -2483,16 +2498,26 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
return 1;
msr_info->data = vcpu->arch.osvw.length;
break;
case MSR_AMD64_OSVW_STATUS:
if (!guest_cpuid_has_osvw(vcpu))
return 1;
msr_info->data = vcpu->arch.osvw.status;
break;
+ case MSR_PLATFORM_INFO:
+ msr_info->data = 0;
+ if (vcpu->arch.cpuid_fault_supported)
+ msr_info->data |= PLATINFO_CPUID_FAULT;
+ break;
+ case MSR_MISC_FEATURES_ENABLES:
+ msr_info->data = 0;
+ if (vcpu->arch.cpuid_fault)
+ msr_info->data |= CPUID_FAULT_ENABLE;
+ break;
default:
if (kvm_pmu_is_valid_msr(vcpu, msr_info->index))
return kvm_pmu_get_msr(vcpu, msr_info->index, &msr_info->data);
if (!ignore_msrs) {
vcpu_unimpl(vcpu, "unhandled rdmsr: 0x%x\n", msr_info->index);
return 1;
} else {
vcpu_unimpl(vcpu, "ignored rdmsr: 0x%x\n", msr_info->index);
@@ -7508,16 +7533,19 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)

kvm_clear_async_pf_completion_queue(vcpu);
kvm_async_pf_hash_reset(vcpu);
vcpu->arch.apf.halted = false;

if (!init_event) {
kvm_pmu_reset(vcpu);
vcpu->arch.smbase = 0x30000;
+
+ vcpu->arch.cpuid_fault_supported = true;
+ vcpu->arch.cpuid_fault = false;
}

memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));
vcpu->arch.regs_avail = ~0;
vcpu->arch.regs_dirty = ~0;

kvm_x86_ops->vcpu_reset(vcpu, init_event);
}
--
2.10.2
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