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SubjectRe: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512_4FMAPS features to kvm guest
Date
On Fri, 2016-10-28 at 17:12 +0800, He Chen wrote:
> The spec can be found in Intel Software Developer Manual or in
> Instruction Set Extensions Programming Reference.
>
> Signed-off-by: Luwei Kang <luwei.kang@intel.com>
> Signed-off-by: He Chen <he.chen@linux.intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index afa7bbb..328b169 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -376,6 +376,10 @@ static inline int __do_cpuid_ent(struct
> kvm_cpuid_entry2 *entry, u32 function,
>   /* cpuid 7.0.ecx*/
>   const u32 kvm_cpuid_7_0_ecx_x86_features = F(PKU) | 0
> /*OSPKE*/;
>  
> + /* cpuid 7.0.edx*/
> + const u32 kvm_cpuid_7_0_edx_x86_features =
> +        0x4 /* AVX512-4VNNIW */ | 0x8 /* AVX512-4FMAPS */;
> +
>   /* all calls to cpuid_count() should be made on the same cpu
> */
>   get_cpu();
>  
> @@ -458,12 +462,13 @@ static inline int __do_cpuid_ent(struct
> kvm_cpuid_entry2 *entry, u32 function,
>   /* PKU is not yet implemented for shadow
> paging. */
>   if (!tdp_enabled)
>   entry->ecx &= ~F(PKU);
> +            entry->edx &= kvm_cpuid_7_0_edx_x86_features;

The cpu_mask() is missed here.
I understand that it doesn't work for this scattered features but the
bits in edx must be zeroed if corresponding flags were cleared in
fpu__xstate_clear_all_cpu_caps.
So this implies more work unfortunately.

>   } else {
>   entry->ebx = 0;
>   entry->ecx = 0;
> +            entry->edx = 0;
>   }
>   entry->eax = 0;
> - entry->edx = 0;
>   break;
>   }
>   case 9:
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