linux-kernel - Re: [PATCH v1 7/8] KVM: x86: Expose PEBS feature to guest

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Message-ID: <20191029150531.GN4097@hirez.programming.kicks-ass.net>
Date:   Tue, 29 Oct 2019 16:05:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luwei Kang <luwei.kang@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, rkrcmar@...hat.com,
        sean.j.christopherson@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, ak@...ux.intel.com, thomas.lendacky@....com,
        acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org
Subject: Re: [PATCH v1 7/8] KVM: x86: Expose PEBS feature to guest

On Sun, Oct 27, 2019 at 07:11:16PM -0400, Luwei Kang wrote:
> Expose PEBS feature to guest by IA32_MISC_ENABLE[bit12].
> IA32_MISC_ENABLE[bit12] is Processor Event Based Sampling (PEBS)
> Unavailable (RO) flag:
> 1 = PEBS is not supported; 0 = PEBS is supported.

Why does it make sense to expose this on SVM?

> Signed-off-by: Luwei Kang <luwei.kang@...el.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/svm.c              |  6 ++++++
>  arch/x86/kvm/vmx/vmx.c          |  1 +
>  arch/x86/kvm/x86.c              | 22 +++++++++++++++++-----
>  4 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 24a0ab9..76f5fa5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1127,6 +1127,7 @@ struct kvm_x86_ops {
>  	bool (*xsaves_supported)(void);
>  	bool (*umip_emulated)(void);
>  	bool (*pt_supported)(void);
> +	bool (*pebs_supported)(void);
>  	bool (*pdcm_supported)(void);
>  
>  	int (*check_nested_events)(struct kvm_vcpu *vcpu, bool external_intr);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 7e0a7b3..3a1bbb3 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5975,6 +5975,11 @@ static bool svm_pt_supported(void)
>  	return false;
>  }
>  
> +static bool svm_pebs_supported(void)
> +{
> +	return false;
> +}
> +
>  static bool svm_pdcm_supported(void)
>  {
>  	return false;
> @@ -7277,6 +7282,7 @@ static bool svm_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
>  	.xsaves_supported = svm_xsaves_supported,
>  	.umip_emulated = svm_umip_emulated,
>  	.pt_supported = svm_pt_supported,
> +	.pebs_supported = svm_pebs_supported,
>  	.pdcm_supported = svm_pdcm_supported,
>  
>  	.set_supported_cpuid = svm_set_supported_cpuid,
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 5c4dd05..3c370a3 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7879,6 +7879,7 @@ static __exit void hardware_unsetup(void)
>  	.xsaves_supported = vmx_xsaves_supported,
>  	.umip_emulated = vmx_umip_emulated,
>  	.pt_supported = vmx_pt_supported,
> +	.pebs_supported = vmx_pebs_supported,
>  	.pdcm_supported = vmx_pdcm_supported,
>  
>  	.request_immediate_exit = vmx_request_immediate_exit,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 661e2bf..5f59073 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2591,6 +2591,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
>  int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  {
>  	bool pr = false;
> +	bool update_cpuid = false;
>  	u32 msr = msr_info->index;
>  	u64 data = msr_info->data;
>  
> @@ -2671,11 +2672,17 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		    ((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;
> +			update_cpuid = true;
>  		}
> +
> +		if (kvm_x86_ops->pebs_supported())
> +			data &=  ~MSR_IA32_MISC_ENABLE_PEBS;

whitespace damage

> +		else
> +			data |= MSR_IA32_MISC_ENABLE_PEBS;
> +
> +		vcpu->arch.ia32_misc_enable_msr = data;
> +		if (update_cpuid)
> +			kvm_update_cpuid(vcpu);
>  		break;
>  	case MSR_IA32_SMBASE:
>  		if (!msr_info->host_initiated)
> @@ -2971,7 +2978,12 @@ 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:
> -		msr_info->data = vcpu->arch.ia32_misc_enable_msr;
> +		if (kvm_x86_ops->pebs_supported())
> +			msr_info->data = (vcpu->arch.ia32_misc_enable_msr &
> +						~MSR_IA32_MISC_ENABLE_PEBS);
> +		else
> +			msr_info->data = (vcpu->arch.ia32_misc_enable_msr |
> +						MSR_IA32_MISC_ENABLE_PEBS);

Coding style violation.

>  		break;
>  	case MSR_IA32_SMBASE:
>  		if (!msr_info->host_initiated)
> -- 
> 1.8.3.1
>