Re: [libvirt] [PATCH 0/3] sample: vfio mdev display devices.

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 24 Apr 2018 09:17:37 +0200
Gerd Hoffmann <kraxel@redhat.com> wrote:

>   Hi,
> 
> > Here's another proposal that's really growing on me:
> > 
> >  * Fix the vendor drivers!  Allow devices to be opened and probed
> >    without these external dependencies.  
> 
> Hmm.  If you try use gvt with tcg then, wouldn't qemu think "device
> probed ok, all green" then even though that isn't the case?

Well, is there a way to make it work with tcg?  That would be the best
solution.  Perhaps KVM could be handled as an accelerator rather than a
required component.  I don't really understand how the page tracking
interface is used and why it's not required by NVIDIA if it's so
fundamental to GVT-g.  Otherwise, are there other points at which the
device could refuse to be enabled, for instance what if the write to
enable bus-master in the PCI command register returned an error if the
device isn't fully configured.  Paolo had suggested offline that maybe
there could be a read-only mode of the device that allows probing.  I
think that would be a fair bit of work and complexity to support, but
I'm open to those sorts of ideas.  I can't be sure the NVIDIA
requirement isn't purely for accounting purposes within their own
proprietary userspace manager, without any real technical requirement.
Hoping Intel and NVIDIA can comment on these so we really understand
why these are in place before we bend over backwards for a secondary API
interface. Thanks,

Alex