Re: Problem with KVM guest switching to x86 long mode

[Pekka Enberg <penberg@cs.helsinki.fi>]

Avi Kivity wrote:
> On 04/11/2010 12:48 PM, Pekka Enberg wrote:
>>> So the guest is in long mode, happily trying to access pci config space.
>>>
>>> MAXPHYADDR comes from cpuid 80000008.eax[0:7].  Typical values are 
>>> 36-40 (number of physical address bits supported by the processor).  
>>> What value does your guest see?
>>
>>
>> Ah, nice catch! The host cpuid doesn't seem to support 80000008 at so 
>> I didn't set it up in the guest either. I now added dummy emulation 
>> for it and the triple fault is fixed.
> 
> It should work without 80000008 set up - failure should happen only if 
> it is setup incorrectly:
> 
> int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
> {
>     struct kvm_cpuid_entry2 *best;
> 
>     best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
>     if (best)
>         return best->eax & 0xff;
>     return 36;
> }

Well, like I said, if I don't add an entry for it in struct kvm_cpuid2 
that's passed to KVM_SET_CPUID2 ioctl, I see a triple fault on Core 2 
Duo CPU that doesn't seem to have native 0x80000008.

			Pekka