Re: vga passthrough with qemu-xen (or qemu upstream)

["Pasi Kärkkäinen" <pasik@iki.fi>]

Hello,

On Mon, Jan 20, 2014 at 01:24:23PM +0000, Wu, Feng wrote:
> 
> 
> > >>> >
> > >>> > Hi all,
> > >>> >
> > >>> > Is it possible to do vga passthrough on xen-unstable with qemu-xen as
> > >>> > device model? I tried but I am getting error 'gfx_passthru' invalid
> > >>> > parameter for qemu-xen. I am able to do passthrough with qemu
> > >>> > traditional i.e. qemu-dm.
> > >>>
> > >>> As far as I know, only qemu-traditional supports vga pass-through
> > >>> right now.
> > >>
> > >> Right.
> > >> It is not possible to assign your primary VGA card to a VM with
> > >> qemu-xen. You should be able to assign your secondary VGA card though.
> > >
> > > Let me understand this correctly. If I have two VGA cards then I can
> > > passthrough
> > > secondary VGA card (in Dom0) to HVM as its primary VGA card. Is this
> > > right and
> > > if yes how can I do it?
> > 
> > Passing any VGA card as a primary-in-domU has always been problematic.
> 
> I think passing VGA card as a primary-in-domU works well in Qemu-traditional, right?
> 

primary-in-domU requires vendor specific hacks in Xen qemu.
qemu-traditional includes many patches for Intel IGD primary passthru support,
but patches for AMD/ATI and Nvidia GPUs aren't merged to qemu-traditional. 

There unapplied patches for qemu-traditional (AMD/Nvidia) GPU passthru are in 
various source trees, mailinglist archives, and on some blogs around the internet.

Also for Intel IGD I think there's at least one outstanding patch/fix that 
hasn't been merged to qemu-traditional yet, see:

http://lists.xenproject.org/archives/html/xen-devel/2013-02/msg00538.html
http://lists.xen.org/archives/html/xen-devel/2013-07/msg01385.html

The patch in question probably needs some work before it is suitable for being applied to qemu-traditional.


> 
> Thanks,
> Feng
> 

-- Pasi