Re: [Qemu-devel] Cirrus bugs vs endian: how two bugs cancel each other out

[Benjamin Herrenschmidt]

On Tue, 2012-08-07 at 07:30 +0200, Gerd Hoffmann wrote:
> On 08/06/12 23:16, Benjamin Herrenschmidt wrote:
> > On Mon, 2012-08-06 at 15:20 +0200, Gerd Hoffmann wrote:
> >> There are discussions about re-doing the guest/host interface (command
> >> rings etc) now and then, by adding a qxl2 device (or maybe even extend
> >> stdvga), dropping a bunch of backward compatibility stuff in qxl.c.
> >>
> >> Sending the spice commands over virtio is certainly an option here.
> >> I'm
> >> not sure it is possible to drive virtio rings from userspace (Xorg
> >> driver), but that issue should go away with the qxl kms driver in the
> >> works.
> > 
> > Anything that gets rid of the qxl memory region API is welcome ;-) Some
> > of that stuff is really gross.
> 
> Well, it is needed for sanity checking memory references (to images etc)
> in qxl commands, so we can't just zap it.  But having a kms driver in
> kernel space makes things easier again:  You could simply register a
> single memory region for the guest ram, then basically use guest
> physical addresses for qxl memory references.  qxl commands & data can
> live in guest ram and you can stick references to the commands into
> virtio rings ...

Or you use a sane model in the first place that hides memory references
behind object IDs :-) Yes, going via a KMS driver will go a long way
toward fixing some of that.

I would still like to experiment a bit if time permits with a different
model which is basically GL paravirt via a virtio channel on top of
virtio-vga (possibly limited to GL/ES at least initially).

Guest side, we'd then have a simple DRM and use Glamor to turn all 2D
rendering into GL.

Cheers,
Ben.