linux-kernel - Re: [PATCH 6/6] KVM: x86: Set KVM LASS based on hardware capability

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Date:   Tue, 25 Apr 2023 10:57:08 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     Zeng Guang <guang.zeng@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        H Peter Anvin <hpa@...or.com>, kvm@...r.kernel.org
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Gao Chao <chao.gao@...el.com>
Subject: Re: [PATCH 6/6] KVM: x86: Set KVM LASS based on hardware capability



On 4/20/2023 9:37 PM, Zeng Guang wrote:
> Host kernel may clear LASS capability in boot_cpu_data.x86_capability
Is there some option to do it?

> besides explicitly using clearcpuid parameter. That will cause guest
> not being able to manage LASS independently. So set KVM LASS directly
> based on hardware capability to eliminate the dependency.
>
> Add new helper functions to facilitate getting result of CPUID sub-leaf.
>
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> ---
>   arch/x86/include/asm/cpuid.h | 36 ++++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/cpuid.c         |  4 ++++
>   2 files changed, 40 insertions(+)
>
> diff --git a/arch/x86/include/asm/cpuid.h b/arch/x86/include/asm/cpuid.h
> index 9bee3e7bf973..a25dd00b7c0a 100644
> --- a/arch/x86/include/asm/cpuid.h
> +++ b/arch/x86/include/asm/cpuid.h
> @@ -127,6 +127,42 @@ static inline unsigned int cpuid_edx(unsigned int op)
>   	return edx;
>   }
>   
> +static inline unsigned int cpuid_count_eax(unsigned int op, int count)
> +{
> +	unsigned int eax, ebx, ecx, edx;
> +
> +	cpuid_count(op, count, &eax, &ebx, &ecx, &edx);
> +
> +	return eax;
> +}
> +
> +static inline unsigned int cpuid_count_ebx(unsigned int op, int count)
> +{
> +	unsigned int eax, ebx, ecx, edx;
> +
> +	cpuid_count(op, count, &eax, &ebx, &ecx, &edx);
> +
> +	return ebx;
> +}
> +
> +static inline unsigned int cpuid_count_ecx(unsigned int op, int count)
> +{
> +	unsigned int eax, ebx, ecx, edx;
> +
> +	cpuid_count(op, count, &eax, &ebx, &ecx, &edx);
> +
> +	return ecx;
> +}
> +
> +static inline unsigned int cpuid_count_edx(unsigned int op, int count)
> +{
> +	unsigned int eax, ebx, ecx, edx;
> +
> +	cpuid_count(op, count, &eax, &ebx, &ecx, &edx);
> +
> +	return edx;
> +}
> +
>   static __always_inline bool cpuid_function_is_indexed(u32 function)
>   {
>   	switch (function) {
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 5facb8037140..e99b99ebe1fe 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -667,6 +667,10 @@ void kvm_set_cpu_caps(void)
>   		F(AMX_FP16) | F(AVX_IFMA)
>   	);
>   
> +	/* Set LASS based on hardware capability */
> +	if (cpuid_count_eax(7, 1) & F(LASS))
> +		kvm_cpu_cap_set(X86_FEATURE_LASS);
> +
>   	kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX,
>   		F(AVX_VNNI_INT8) | F(AVX_NE_CONVERT) | F(PREFETCHITI)
>   	);