linux-kernel - Re: [PATCH v5 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT

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Message-ID: <b2cfa1d015315c74af6cee1c00185e5c68cfa397.camel@linux.intel.com>
Date:   Thu, 20 Jun 2019 17:46:45 +0800
From:   Xiaoyao Li <xiaoyao.li@...ux.intel.com>
To:     Tao Xu <tao3.xu@...el.com>, pbonzini@...hat.com,
        rkrcmar@...hat.com, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        sean.j.christopherson@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        fenghua.yu@...el.com, jingqi.liu@...el.com
Subject: Re: [PATCH v5 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

On Thu, 2019-06-20 at 16:46 +0800, Tao Xu wrote:
> UMWAIT and TPAUSE instructions use IA32_UMWAIT_CONTROL at MSR index E1H
> to determines the maximum time in TSC-quanta that the processor can reside
> in either C0.1 or C0.2.
> 
> This patch emulates MSR IA32_UMWAIT_CONTROL in guest and differentiate
> IA32_UMWAIT_CONTROL between host and guest. The variable
> mwait_control_cached in arch/x86/power/umwait.c caches the MSR value, so
> this patch uses it to avoid frequently rdmsr of IA32_UMWAIT_CONTROL.
> 
> Co-developed-by: Jingqi Liu <jingqi.liu@...el.com>
> Signed-off-by: Jingqi Liu <jingqi.liu@...el.com>
> Signed-off-by: Tao Xu <tao3.xu@...el.com>
> ---
> 
> Changes in v5:
> 	remove vmx_waitpkg_supported() to fix guest can rdmsr or wrmsr
> 	when the feature is off (Xiaoyao)
> 	remove the atomic_switch_ia32_umwait_control() and move the
> 	codes into vmx_set_msr()
> 	rebase the patch because the kernel dependcy patch updated to
> 	v5: https://lkml.org/lkml/2019/6/19/972
> ---
>  arch/x86/kernel/cpu/umwait.c |  3 ++-
>  arch/x86/kvm/vmx/vmx.c       | 24 ++++++++++++++++++++++++
>  arch/x86/kvm/vmx/vmx.h       |  3 +++
>  arch/x86/kvm/x86.c           |  1 +
>  4 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/umwait.c b/arch/x86/kernel/cpu/umwait.c
> index 4b2aff7b2d4d..db5c193ef136 100644
> --- a/arch/x86/kernel/cpu/umwait.c
> +++ b/arch/x86/kernel/cpu/umwait.c
> @@ -15,7 +15,8 @@
>   * MSR value. By default, umwait max time is 100000 in TSC-quanta and C0.2
>   * is enabled
>   */
> -static u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000,
> UMWAIT_C02_ENABLED);
> +u32 umwait_control_cached = UMWAIT_CTRL_VAL(100000, UMWAIT_C02_ENABLED);
> +EXPORT_SYMBOL_GPL(umwait_control_cached);
>  
>  /*
>   * Serialize access to umwait_control_cached and IA32_UMWAIT_CONTROL MSR
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b35bfac30a34..0fb55c8426e2 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1679,6 +1679,12 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct
> msr_data *msr_info)
>  #endif
>  	case MSR_EFER:
>  		return kvm_get_msr_common(vcpu, msr_info);
> +	case MSR_IA32_UMWAIT_CONTROL:
> +		if (!guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
> +			return 1;
> +
> +		msr_info->data = vmx->msr_ia32_umwait_control;
> +		break;
>  	case MSR_IA32_SPEC_CTRL:
>  		if (!msr_info->host_initiated &&
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
> @@ -1841,6 +1847,22 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct
> msr_data *msr_info)
>  			return 1;
>  		vmcs_write64(GUEST_BNDCFGS, data);
>  		break;
> +	case MSR_IA32_UMWAIT_CONTROL:
> +		if (!guest_cpuid_has(vcpu, X86_FEATURE_WAITPKG))
> +			return 1;
> +
> +		/* The reserved bit IA32_UMWAIT_CONTROL[1] should be zero */
> +		if (data & BIT_ULL(1))
> +			return 1;
> +
> +		vmx->msr_ia32_umwait_control = data;
> +		if (vmx->msr_ia32_umwait_control != umwait_control_cached)
> +			add_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL,
> +				vmx->msr_ia32_umwait_control,
> +				umwait_control_cached, false);
> +		else
> +			clear_atomic_switch_msr(vmx, MSR_IA32_UMWAIT_CONTROL);

You cannot put the atomic switch here. What if umwait_control_cached is changed
at runtime? Host kernel patch exposed a sysfs interface to let it happen.

> +		break;
>  	case MSR_IA32_SPEC_CTRL:
>  		if (!msr_info->host_initiated &&
>  		    !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL))
> @@ -4126,6 +4148,8 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool
> init_event)
>  	vmx->rmode.vm86_active = 0;
>  	vmx->spec_ctrl = 0;
>  
> +	vmx->msr_ia32_umwait_control = 0;
> +
>  	vcpu->arch.microcode_version = 0x100000000ULL;
>  	vmx->vcpu.arch.regs[VCPU_REGS_RDX] = get_rdx_init_val();
>  	kvm_set_cr8(vcpu, 0);
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 61128b48c503..8485bec7c38a 100644
> --- a/arch/x86/kvm/vmx/vmx.h
> +++ b/arch/x86/kvm/vmx/vmx.h
> @@ -14,6 +14,8 @@
>  extern const u32 vmx_msr_index[];
>  extern u64 host_efer;
>  
> +extern u32 umwait_control_cached;
> +
>  #define MSR_TYPE_R	1
>  #define MSR_TYPE_W	2
>  #define MSR_TYPE_RW	3
> @@ -194,6 +196,7 @@ struct vcpu_vmx {
>  #endif
>  
>  	u64		      spec_ctrl;
> +	u64		      msr_ia32_umwait_control;
>  
>  	u32 vm_entry_controls_shadow;
>  	u32 vm_exit_controls_shadow;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 83aefd759846..4480de459bf4 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1138,6 +1138,7 @@ static u32 msrs_to_save[] = {
>  	MSR_IA32_RTIT_ADDR1_A, MSR_IA32_RTIT_ADDR1_B,
>  	MSR_IA32_RTIT_ADDR2_A, MSR_IA32_RTIT_ADDR2_B,
>  	MSR_IA32_RTIT_ADDR3_A, MSR_IA32_RTIT_ADDR3_B,
> +	MSR_IA32_UMWAIT_CONTROL,
>  };
>  
>  static unsigned num_msrs_to_save;