Re: [Qemu-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

[Paolo Bonzini <pbonzini@redhat.com>]

Il 25/06/2014 16:10, Michael S. Tsirkin ha scritto:
> On Wed, Jun 25, 2014 at 03:53:30PM +0200, Paolo Bonzini wrote:
>> Il 25/06/2014 15:47, Michael S. Tsirkin ha scritto:
>>> OK, so how about doing this: either for the ISA
>>> bridge, or for the VGA card itself:
>>>
>>>    set subsystem vendor id to PCI_VENDOR_ID_XEN,
>>>    set subsystem device id to PCH device id
>>
>> That would work, but the same problem would then arise for the MCH.  The
>> driver there is banging at random places in the configuration space.
>>
>> This is why I asked for a solution that is future-proof, and since you can
>> make one that works for both MCH and PCH it is nice to do the work just
>> once.
>
> Q35 has MCH, so I don't see why we can't make that work,
> extending it as appropriate.

Is Q35's MCH configuration space entirely compatible with newer chipsets 
that are in the host and that the IGD driver expects?  I dont think it's 
safe to assume that.

> Doing that for PIIX is iffy.
> Should we really do that? Q35 is there.

Xen doesn't support Q35, and Q35 is still lacking migration.  So it's 
really a chicken-and-egg problem.

Paolo