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RE: [Xen-devel] [RFC] Hypercalls from HVM guests

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, "Steve Ofsthun" <sofsthun@xxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [RFC] Hypercalls from HVM guests
From: "Nakajima, Jun" <jun.nakajima@xxxxxxxxx>
Date: Sat, 8 Apr 2006 16:33:19 -0700
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Thread-topic: [Xen-devel] [RFC] Hypercalls from HVM guests
Keir Fraser wrote:
> On 7 Apr 2006, at 20:30, Steve Ofsthun wrote:
>>> Actually, maybe using an unused index for CPUID (e.g. 0xb0000000)
>>> would be better? As that's defined to return all zero's, and not
>>> cause any traps whatever value you use (unless the CPU is so old
>>> that it doesn't support CPUID, of course).
>> This sounds encouraging, but is CPUID always trapped by the HVM code?
> It can be, and in practise yes it is so this could work.
>   -- Keir
If eax is set to a value outside the recognized range of CPUID currently
defined, CPUID does not necessarily return all zero's on Intel. It's
"Reserved" (Information returned for highest basic information leaf).
Also "an unused index" can have conflicts in the future.

If we just need to tell on which CPU the current HVM guest is running, I
think "GeunineIntel" or "AuthenticAMD" is the best because it's been
used by native systems as well. 

Intel Open Source Technology Center

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