Re: A couple of HVMlite loose ends

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 13/01/16 16:13, Jan Beulich wrote:
>>>> On 13.01.16 at 16:49, <roger.pau@citrix.com> wrote:
>> Hello,
>>
>> While working on a HVMlite Dom0 implementation I've found a couple of
>> loose ends with the design that I would like to comment because it's not
>> clear to me what's the best direction to take.
>>
>> 1. HVM CPUID and Dom0.
>>
>> Sadly the way CPUID is handled inside of Xen varies between PV and HVM.
>> On PV guests AFAICT we mostly do black-listing (I think this is the
>> right term), which means we pick the native CPUID result and then
>> perform a series of filter operations in order to remove features which
>> should not be exposed to a PV guest. On the other hand, for HVM guests
>> we pre-populate an array (d->arch.cpuids) during domain build time, and
>> the contents of that array is what is returned to the guest when a CPUID
>> instruction is executed.
> This d->arch.cpuids[] mechanism is common to HVM and PV; the
> exception really is Dom0.

Dom0 is not special when it comes to cpuid, and shouldn't be treated as
such.  My longter term CPUID plans will be fixing this.

~Andrew