linux-kernel - Re: [PATCH v2 3/3] KVM: X86: Emulate MSR_IA32_MISC

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Date:   Tue, 4 Jun 2019 18:59:26 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Subject: Re: [PATCH v2 3/3] KVM: X86: Emulate MSR_IA32_MISC_ENABLE MWAIT bit

On 21/05/19 08:06, Wanpeng Li wrote:
> 
> 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 needs some adjustment so that the default is backwards-compatible:

diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index e3ae96b52a16..f9b021e16ebc 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -378,11 +378,11 @@ struct kvm_sync_regs {
 	struct kvm_vcpu_events events;
 };
 
-#define KVM_X86_QUIRK_LINT0_REENABLED	(1 << 0)
-#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_X86_QUIRK_LINT0_REENABLED	   (1 << 0)
+#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
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f54d266fd3b5..bfa1341ce6f1 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -137,10 +137,10 @@ 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)) {
+	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)
+			if (vcpu->arch.ia32_misc_enable_msr & MSR_IA32_MISC_ENABLE_NO_MWAIT)
 				best->ecx |= F(MWAIT);
 			else
 				best->ecx &= ~F(MWAIT);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 528935733fe0..0c1498da46c7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2548,17 +2548,15 @@ 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_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;
-			}
+		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_NO_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;
 		}
-		vcpu->arch.ia32_misc_enable_msr = data;
 		break;
 	case MSR_IA32_SMBASE:
 		if (!msr_info->host_initiated)

Please double check, in the meanwhile I've queued the patch.

Paolo