Re: [PATCH 0/3] x86: enlightenment for ticket spinlocks

From: Jan Beulich
Date: Mon Feb 01 2010 - 02:56:45 EST


>>> "H. Peter Anvin" <hpa@xxxxxxxxx> 31.01.10 19:43 >>>
>On 01/31/2010 10:02 AM, Jan Beulich wrote:
>>>>> "H. Peter Anvin" 01/31/10 2:42 AM >>>
>>> + * EBX-EDX: "XenVMMXenVMM" signature, allowing positive identification
>>> + * of a Xen host.
>>> + */
>>> +#define XEN_CPUID_SIGNATURE_EBX 0x566e6558 /* "XenV" */
>>> +#define XEN_CPUID_SIGNATURE_ECX 0x65584d4d /* "MMXe" */
>>> +#define XEN_CPUID_SIGNATURE_EDX 0x4d4d566e /* "nVMM" */
>>>
>>> I hope you know this spells "MMXenVMMXenV". The ordering is ecx-edx-ebx
>>> (register numbers 1, 2, 3).
>>
>> According to the documentation I have, the ordering is EBX-EDX-ECX,
>> so indeed the spelling would seem broken, but since this is an interface
>> header taken directly from Xen, it's got to be (and it works) that way.
>> Odd.
>>
>
>It's probably a bug that's now cast in stone. That happends. I just
>had to be picky. (And yes, it's ebx-edx-ecx; see my second email.)

The "good" thing is that this is not on leaf 0, but on leaf 0x4000??00,
i.e. "normal" code would never display this garbled string.

Jan

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