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

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Message-ID: <0F74F27F-2403-441D-8702-373BDA21E3A7@oracle.com>
Date:   Mon, 13 May 2019 07:22:32 -0400
From:   Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:     Wanpeng Li <kernellwp@...il.com>, 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: Re: [PATCH] KVM: X86: Enable IA32_MSIC_ENABLE MONITOR bit when exposing mwait/monitor

On May 13, 2019 5:46:39 AM EDT, Wanpeng Li <kernellwp@...il.com> wrote:
>From: Wanpeng Li <wanpengli@...cent.com>
>
>MSR IA32_MSIC_ENABLE bit 18, according to SDM:
>

 MSIC? (Also the $subject)


>| 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;