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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 9 Apr 2006, at 00:33, Nakajima, Jun wrote:

> 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.
Then how do you tell whether you are running on a hypervisor without 
executing some instruction that might fault? We would like to avoid 
requiring that.
There is quite a lot of CPUID and MSR address space, and a random 
return value for CPUID when running natively is practically-speaking 
fine if we're looking for a 128-bit signature.
The only other option I think would be a BIOS table, probably below 
1MB. I prefer the CPUID/MSR method.
 -- Keir


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