Re: [Xen-devel] [PATCH] x86: correct CPUID output for out of bounds input

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/09/16 16:27, Jan Beulich wrote:
>
>>> +        {
>>> +            if ( d->arch.x86_vendor == X86_VENDOR_AMD )
>>> +            {
>>> +                *eax = 0;
>>> +                *ebx = 0;
>>> +                *ecx = 0;
>>> +                *edx = 0;
>>> +                return;
>>> +            }
>>> +            if ( input >> 16 )
>>> +                hvm_cpuid(0, &lvl, NULL, NULL, NULL);
>> Is this really the right way round?  The AMD method of "reserved always
>> as zero" is the more sane default to take.
> If anything I'd then say let's _always_ follow the AMD model.

It would certainly be better to default to AMD, and special case others
on an as-needed basis.

Strictly speaking, following the AMD model is compatible with the
"Reserved" nature specified for Intel.

Lets just go with this.

~Andrew

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