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SubjectRe: [PATCH 6/6] KVM: x86: Set KVM LASS based on hardware capability
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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@intel.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)
> );

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