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

[Paolo Bonzini]

On 31/10/2016 11:30, Borislav Petkov wrote:
> On Mon, Oct 31, 2016 at 10:18:41AM +0000, Luc, Piotr wrote:
>> The cpuid_mask function, which usually used in kvm, read bit from this
>> x86_capabity and mask out. This prevents passing disabled features to
>> guest. If we use cpu_count instead, which reports bits directly from
> 
> Ah, you mean cpuid_count().
> 
>> CPU, then the bits of features that are disabled in host are passed to
>> guest as enabled. This seems be inconsistent.
> 
> Ok, I see what you mean.
> 
> So I guess we'll have to iterate over the cpuid_bits[] array and
> recreate the CPUID leaf for KVM instead, as I suggested earlier.

Yes, indeed. :(

The information is all in arch/x86/kernel/cpu/scattered.c's cpuid_bits
array.  Borislav, would it be okay to export the cpuid_regs enum?

Paolo