linux-kernel - Re: [PATCH] kvm: x86: emulate MSR_PLATFORM

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Date:   Wed, 23 Aug 2023 11:41:46 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Hao Xiang <hao.xiang@...ux.alibaba.com>, kvm@...r.kernel.org
Cc:     shannon.zhao@...ux.alibaba.com, pbonzini@...hat.com,
        seanjc@...gle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: x86: emulate MSR_PLATFORM_INFO msr bits

On 8/21/2023 11:22 AM, Hao Xiang wrote:
> For intel platform, The BzyMhz field of Turbostat shows zero
> due to the missing of part msr bits of MSR_PLATFORM_INFO.
> 
> Acquire necessary msr bits, and expose following msr info to guest,
> to make sure guest can get correct turbo frequency info.
>
> MSR_PLATFORM_INFO bits
> bit 15:8, Maximum Non-Turbo Ratio (MAX_NON_TURBO_LIM_RATIO)
> bit 47:40, Maximum Efficiency Ratio (MAX_EFFICIENCY_RATIO)

I'm curious. How are they related to turbo frequency info?

bits 15:8, tell the Non-turbo frequency and bits 47:40 tells the min 
frequency.

> Signed-off-by: Hao Xiang <hao.xiang@...ux.alibaba.com>
> ---
>   arch/x86/include/asm/msr-index.h |  4 ++++
>   arch/x86/kvm/x86.c               | 25 ++++++++++++++++++++++++-
>   2 files changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
> index 1d11135..1c8a276 100644
> --- a/arch/x86/include/asm/msr-index.h
> +++ b/arch/x86/include/asm/msr-index.h
> @@ -68,6 +68,10 @@
>   #define MSR_PLATFORM_INFO		0x000000ce
>   #define MSR_PLATFORM_INFO_CPUID_FAULT_BIT	31
>   #define MSR_PLATFORM_INFO_CPUID_FAULT		BIT_ULL(MSR_PLATFORM_INFO_CPUID_FAULT_BIT)
> +/* MSR_PLATFORM_INFO bit 15:8, Maximum Non-Turbo Ratio (MAX_NON_TURBO_LIM_RATIO) */
> +#define MSR_PLATFORM_INFO_MAX_NON_TURBO_LIM_RATIO	0x00000000ff00
> +/* MSR_PLATFORM_INFO bit 47:40, Maximum Efficiency Ratio (MAX_EFFICIENCY_RATIO) */
> +#define MSR_PLATFORM_INFO_MAX_EFFICIENCY_RATIO		0xff0000000000

They are mask not the value, please name them with _MASK suffix.

>   
>   #define MSR_IA32_UMWAIT_CONTROL			0xe1
>   #define MSR_IA32_UMWAIT_CONTROL_C02_DISABLE	BIT(0)
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c381770..621c3e1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1679,6 +1679,29 @@ static u64 kvm_get_arch_capabilities(void)
>   	return data;
>   }
>   
> +
> +static u64 kvm_get_msr_platform_info(void)
> +{
> +	u64 msr_platform_info = 0;
> +
> +	rdmsrl_safe(MSR_PLATFORM_INFO, &msr_platform_info);
> +	/*
> +	 * MSR_PLATFORM_INFO bits:
> +	 * bit 15:8, Maximum Non-Turbo Ratio (MAX_NON_TURBO_LIM_RATIO)
> +	 * bit 31, CPUID Faulting Enabled (CPUID_FAULTING_EN)
> +	 * bit 47:40, Maximum Efficiency Ratio (MAX_EFFICIENCY_RATIO)
> +	 *
> +	 * Emulate part msr bits, expose above msr info to guest,
> +	 * to make sure guest can get correct turbo frequency info.
> +	 */
> +
> +	msr_platform_info &= (MSR_PLATFORM_INFO_MAX_NON_TURBO_RATIO |
> +			MSR_PLATFORM_INFO_MAX_EFFICIENCY_RATIO);
> +	msr_platform_info |= MSR_PLATFORM_INFO_CPUID_FAULT;
> +
> +	return msr_platform_info;
> +}
> +
>   static int kvm_get_msr_feature(struct kvm_msr_entry *msr)
>   {
>   	switch (msr->index) {
> @@ -11919,7 +11942,7 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
>   		goto free_guest_fpu;
>   
>   	vcpu->arch.arch_capabilities = kvm_get_arch_capabilities();
> -	vcpu->arch.msr_platform_info = MSR_PLATFORM_INFO_CPUID_FAULT;
> +	vcpu->arch.msr_platform_info = kvm_get_msr_platform_info();
>   	kvm_xen_init_vcpu(vcpu);
>   	kvm_vcpu_mtrr_init(vcpu);
>   	vcpu_load(vcpu);