[PATCH v2 3/3] KVM: X86: Emulate MSR_IA32_MISC_ENABLE MWAIT bit

[Wanpeng Li]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

MSR IA32_MISC_ENABLE bit 18, according to SDM:

| When this bit is set to 0, the MONITOR feature flag is not set (CPUID.01H:ECX[bit 3] = 0).
| This indicates that MONITOR/MWAIT are not supported.
|
| Software attempts to execute MONITOR/MWAIT will cause #UD when this bit is 0.
|
| When this bit is set to 1 (default), MONITOR/MWAIT are supported (CPUID.01H:ECX[bit 3] = 1).

The CPUID.01H:ECX[bit 3] ought to mirror the value of the MSR bit,
CPUID.01H:ECX[bit 3] is a better guard than kvm_mwait_in_guest().
kvm_mwait_in_guest() affects the behavior of MONITOR/MWAIT, not its
guest visibility.

This patch implements toggling of the CPUID bit based on guest writes
to the MSR.

Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Cc: Liran Alon <liran.alon@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
---
v1 -> v2:
 * hide behind KVM_CAP_DISABLE_QUIRKS

 arch/x86/include/uapi/asm/kvm.h |  1 +
 arch/x86/kvm/cpuid.c            | 10 ++++++++++
 arch/x86/kvm/x86.c              | 10 ++++++++++
 3 files changed, 21 insertions(+)

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 7a0e64c..e3ae96b5 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -382,6 +382,7 @@ struct kvm_sync_regs {
 #define KVM_X86_QUIRK_CD_NW_CLEARED	(1 << 1)
 #define KVM_X86_QUIRK_LAPIC_MMIO_HOLE	(1 << 2)
 #define KVM_X86_QUIRK_OUT_7E_INC_RIP	(1 << 3)
+#define KVM_X86_QUIRK_MISC_ENABLE_MWAIT (1 << 4)
 
 #define KVM_STATE_NESTED_GUEST_MODE	0x00000001
 #define KVM_STATE_NESTED_RUN_PENDING	0x00000002
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index e18a9f9..f54d266 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -137,6 +137,16 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 		(best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
 		best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
 
+	if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_MWAIT)) {
+		best = kvm_find_cpuid_entry(vcpu, 0x1, 0);
+		if (best) {
+			if (vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_MWAIT)
+				best->ecx |= F(MWAIT);
+			else
+				best->ecx &= ~F(MWAIT);
+		}
+	}
+
 	/* Update physical-address width */
 	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
 	kvm_mmu_reset_context(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 765fe59..a4eb711 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2547,6 +2547,16 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		}
 		break;
 	case MSR_IA32_MISC_ENABLE:
+		if (kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_MISC_ENABLE_MWAIT) &&
+			((vcpu->arch.ia32_misc_enable_msr ^ data) & MSR_IA32_MISC_ENABLE_MWAIT)) {
+			if ((vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_MWAIT) &&
+				!(data & MSR_IA32_MISC_ENABLE_MWAIT)) {
+				if (!guest_cpuid_has(vcpu, X86_FEATURE_XMM3))
+					return 1;
+			}
+			vcpu->arch.ia32_misc_enable_msr = data;
+			kvm_update_cpuid(vcpu);
+		}
 		vcpu->arch.ia32_misc_enable_msr = data;
 		break;
 	case MSR_IA32_SMBASE:
-- 
2.7.4