Re: [PATCH RFC] kvm: x86: Expose AVX512_BF16 feature to guest

[Jing Liu]

Hi Paolo,

After thinking more, I found way to satisfy all cases in a easy way.
How about things like this?

@@ -507,12 +510,26 @@ static inline int __do_cpuid_ent(struct 
kvm_cpuid_entry2 *entry, u32 fu
                         * if the host doesn't support it.
                         */
                        entry->edx |= F(ARCH_CAPABILITIES);
+               } else if (index == 1) {
+                       entry->eax &= kvm_cpuid_7_1_eax_x86_features;
+                       entry->ebx = 0;
+                       entry->ecx = 0;
+                       entry->edx = 0;
                } else {
+                       entry->eax = 0;
                        entry->ebx = 0;
                        entry->ecx = 0;
                        entry->edx = 0;
                }
-               entry->eax = 0;
+
+               if (index == 0 && entry->eax >= 1) {
+                       entry[1].eax &= kvm_cpuid_7_1_eax_x86_features;
+                       entry[1].ebx = 0;
+                       entry[1].ecx = 0;
+                       entry[1].edx = 0;
+                       entry[1].flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+                       ++*nent;
+               }
                break;
        }


Or you prefer that I update this into another version later?

Thanks!
Jing

On 6/20/2019 11:09 PM, Liu, Jing2 wrote:
> Hi Paolo,
>
> On 6/20/2019 8:16 PM, Paolo Bonzini wrote:
> > On 20/06/19 13:21, Jing Liu wrote:
> > > +ÂÂÂÂÂÂÂ for (i = 1; i <= times; i++) {
> > > +ÂÂÂÂÂÂÂÂÂÂÂ if (*nent >= maxnent)
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ goto out;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ do_cpuid_1_ent(&entry[i], function, i);
> > > +ÂÂÂÂÂÂÂÂÂÂÂ entry[i].eax &= F(AVX512_BF16);
> > > +ÂÂÂÂÂÂÂÂÂÂÂ entry[i].ebx = 0;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ entry[i].ecx = 0;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ entry[i].edx = 0;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ entry[i].flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> > > +ÂÂÂÂÂÂÂÂÂÂÂ ++*nent;
> >
> > This woud be wrong for i > 1, so instead make this
> >
> > ÂÂÂÂif (entry->eax >= 1)
>
> I am confused about the @index parameter. @index seems not used for
> every case except 0x07. Since the caller function only has @index=0, so
> all other cases except 0x07 put cpuid info from subleaf=0 to max subleaf.
>
> What do you think about @index in current function? Does it mean, we
> need put cpuid from index to max subleaf to @entry[i]? If so, the logic
> seems as follows,
>
> if (index == 0) {
>  ÂÂÂ // Put subleaf 0 into @entry
>  ÂÂÂ // Put subleaf 1 into @entry[1]
> } else if (index < entry->eax) {
>  ÂÂÂ // Put subleaf 1 into @entry
> } else {
>  ÂÂÂ // Put all zero into @entry
> }
>
> But this seems not identical with other cases, for current caller
> function. Or we can simply ignore @index in 0x07 and just put all possible
> subleaf info back?
>
> > and define F(AVX512_BF16) as a new constant kvm_cpuid_7_1_eax_features.
> Got it.
>
>
> Thanks,
> Jing
>
> > Paolo