Re: Help with Understanding vcpu xstate restore error during vm migration

[Fonyuy-Asheri Caleb <fonyuy-asheri.caleb@xxxxxxxx>]

>> PV Default policy: 30 leaves, 2 MSRs
>> ...
>>   0000000d:00000000 -> 00000003:00000000:00000240:00000000
>>   0000000d:00000001 -> 00000007:00000000:00000000:00000000
> 
> ... PV guests get nothing, while you're trying to migrate in a guest
> which...
> 
>> =========================================================================================================
>> VM xen-cpuid -p $domid
>> ---------------------------------------------------------------------------------------------------------
>> Domain 3 policy: 31 leaves, 2 MSRs
>> ...
>>   0000000d:00000000 -> 00000007:00000000:00000340:00000000
>>   0000000d:00000001 -> 00000001:00000000:00000000:00000000
>>   0000000d:00000002 -> 00000100:00000240:00000000:00000000
> 
> ... has AVX.

This makes much more sense now. 
> 
> This explains why you're hitting the "guest size > xen size" check.
> 
> Migration should have failed earlier with a clearer message about the VM
> having features not available on the target, but I suspect I know why it
> didn't, and sadly its an item I've had on the todo list for a few years.
> 
> Perhaps the more important question, are you booting the skylake with
> cpuid=no-avx on the command line by any chance?

No. I didn't boot any of the machines with any cpuid modification whatsoever. 

> 
> ~Andrew

Thanks a lot for these pointers Andrew.

Caleb.