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

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

[Wanpeng Li]

From: Wanpeng Li <wanpengli@tencent.com>

MSR IA32_MSIC_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@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Liran Alon <liran.alon@oracle.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
v1 -> v2:
 * to configure MSR_IA32_MISC_ENABLE_MWAIT bit in userspace
 * implements toggling of the CPUID bit based on guest writes to the MSR

 arch/x86/kvm/cpuid.c | 8 ++++++++
 arch/x86/kvm/x86.c   | 9 +++++++++
 2 files changed, 17 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index fd39516..0f82393 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -137,6 +137,14 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 		(best->eax & (1 << KVM_FEATURE_PV_UNHALT)))
 		best->eax &= ~(1 << KVM_FEATURE_PV_UNHALT);
 
+	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 3bbf3ab..4ed45ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2506,6 +2506,15 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		}
 		break;
 	case MSR_IA32_MISC_ENABLE:
+		if ((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