Xen HVM cpuid problem

[Christoph Egger <Christoph.Egger@amd.com>]

Hi Keir,

For HVM guests, all cpuid Fn's going through domain_cpuid()
iterate over the loop and then return 0 for all four registers.

Guests OS's and cpuid tools in HVM which query for
cpuid Fn 0000.0000 %eax and 8000.0000 %eax, see the value 0 and think,
Xen emulates oldish 386/486 CPUs.

This leads to strange boot failures, "your CPU does not support long mode"
or "minimum required CPU is a 486DX CPU" when launching 32bit or 64bit HVM 
guests.

To reproduce this, cpuid is NOT explicitely configured
in the guest config file.

BTW: Is there a reason for not handling cpuid in one central place?

Christoph


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