KVM: X86: Emulate MSR_IA32_MISC_ENABLE MWAIT bit

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@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>
[Fixes for backwards compatibility - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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_NO_MWAIT (1 << 4)
 
 #define KVM_STATE_NESTED_GUEST_MODE	0x00000001
 #define KVM_STATE_NESTED_RUN_PENDING	0x00000002

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_NO_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);

arch/x86/kvm/x86.c

@@ -2547,7 +2547,15 @@ 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_NO_MWAIT) &&
+		    ((vcpu->arch.ia32_misc_enable_msr ^ 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);
+		} else {
+			vcpu->arch.ia32_misc_enable_msr = data;
+		}
 		break;
 	case MSR_IA32_SMBASE:
 		if (!msr_info->host_initiated)