Re: [PATCH] x86/cpuid: expose AVX512_4VNNIW and AVX512_4FMAPS features to kvm guest

[He Chen]

On Fri, Oct 28, 2016 at 11:54:13AM +0200, Paolo Bonzini wrote:
> 
> 
> On 28/10/2016 11:46, He Chen wrote:
> > On Fri, Oct 28, 2016 at 11:31:05AM +0200, Paolo Bonzini wrote:
> >>
> >>
> >> On 28/10/2016 11:12, 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@xxxxxxxxx>
> >>> Signed-off-by: He Chen <he.chen@xxxxxxxxxxxxxxx>
> >>> ---
> >>>  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 */;
> >>
> >> Please define the new features in cpufeature.h first.
> >>
> > These 2 new features defined as scattered features in kernel.
> > In cpufeature.h, there are:
> > #define X86_FEATURE_AVX512_4VNNIW (7*32+16)
> > #define X86_FEATURE_AVX512_4FMAPS (7*32+17)
> > 
> > Please see disscusion here:
> > https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1250183.html
> 
> Uff, that sucks. :(  I'd agree with hpa's position in that thread.
> 
> Please do something like
> 
> 	/* These are scattered features in cpufeature.h.  */
> 	#define KVM_CPUID_BIT_AVX512_4VNNIW	2
> 	#define KVM_CPUID_BIT_AVX512_4FMAPS	3
> 	#define KF(x)	bit(KVM_CPUID_BIT_##x)
> 
> and then
> 
> 	const u32 kvm_cpuid_7_0_edx_x86_features =
> 		KF(AVX512_4VNNIW) | KF(AVX512_4FMAPS)
> 
> I'll think of a trick to avoid using F for scattered features...
> 
Appreciate it :-)