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

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Date:	Mon, 01 Feb 2010 07:56:34 +0000
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<mingo@...e.hu>, <jeremy@...p.org>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] x86: enlightenment for ticket spinlocks

>>> "H. Peter Anvin" <hpa@...or.com> 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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