Re: [Xen-devel] [PATCH] x86/traps: hypervisor leaf 0x40000010 timing info

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 17.09.14 at 18:36, <eshelton@xxxxxxxxx> wrote:
> On Wed, Sep 17, 2014 at 6:05 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>> >>> On 17.09.14 at 06:11, <eshelton@xxxxxxxxx> wrote:
>> As to the patch itself - is this
>>
>> > +    case 5 ... 15:
>> > +        *eax = 0;          /* Reserved */
>> > +        *ebx = 0;          /* Reserved */
>> > +        *ecx = 0;          /* Reserved */
>> > +        *edx = 0;          /* Reserved */
>> > +        break;
>>
>> really needed?
>>
>> Jan
>>
> 
> While looking into this issue, I noticed some CPUID scanning utilities will
> read 0x40000000 to determine the largest leaf, and then read each and every
> leaf up to the largest one (e.g., leaves 0x40000001-0x40000010).  Is it a
> problem if reads to leaves 0x40000005-0x4000000e fall through to the BUG()
> in the default case?  If not, then the 5 ... 15 portion of the switch is
> not needed.

Falling through to a BUG() is of course a problem, but the question
was more towards the zero-initialization (which I thought happens
elsewhere already).

Jan


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