linux-kernel - [PATCH] KVM: X86: Enable IA32_MSIC_ENABLE MONITOR bit when exposing mwait/monitor

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Date:   Mon, 13 May 2019 17:46:39 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: [PATCH] KVM: X86: Enable IA32_MSIC_ENABLE MONITOR bit when exposing mwait/monitor

From: Wanpeng Li <wanpengli@...cent.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). 

This bit should be set to 1, if BIOS enables MONITOR/MWAIT support on host and 
we intend to expose mwait/monitor to the guest.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Liran Alon <liran.alon@...cle.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/x86.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1d89cb9..664449e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2723,6 +2723,13 @@ static int get_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 *pdata, bool host)
 	return 0;
 }
 
+static inline bool kvm_can_mwait_in_guest(void)
+{
+	return boot_cpu_has(X86_FEATURE_MWAIT) &&
+		!boot_cpu_has_bug(X86_BUG_MONITOR) &&
+		boot_cpu_has(X86_FEATURE_ARAT);
+}
+
 int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	switch (msr_info->index) {
@@ -2801,6 +2808,8 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = (u64)vcpu->arch.ia32_tsc_adjust_msr;
 		break;
 	case MSR_IA32_MISC_ENABLE:
+		if (kvm_can_mwait_in_guest() && kvm_mwait_in_guest(vcpu->kvm))
+			vcpu->arch.ia32_misc_enable_msr |= MSR_IA32_MISC_ENABLE_MWAIT;
 		msr_info->data = vcpu->arch.ia32_misc_enable_msr;
 		break;
 	case MSR_IA32_SMBASE:
@@ -2984,13 +2993,6 @@ static int msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs __user *user_msrs,
 	return r;
 }
 
-static inline bool kvm_can_mwait_in_guest(void)
-{
-	return boot_cpu_has(X86_FEATURE_MWAIT) &&
-		!boot_cpu_has_bug(X86_BUG_MONITOR) &&
-		boot_cpu_has(X86_FEATURE_ARAT);
-}
-
 int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 {
 	int r = 0;
-- 
2.7.4