Re: [Xen-devel] vga passthrough with qemu-xen (or qemu upstream)

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 2014-01-20 13:24, Wu, Feng wrote:
> > -----Original Message-----
> > From: xen-devel-bounces@xxxxxxxxxxxxx
> > [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Gordan Bobic
> > Sent: Monday, January 20, 2014 8:50 PM
> > To: xen-devel@xxxxxxxxxxxxx
> > Subject: Re: [Xen-devel] vga passthrough with qemu-xen (or qemu 
> > upstream)
> > On 2014-01-20 12:31, Shakeel Butt wrote:
> > > On Mon, Jan 20, 2014 at 4:09 AM, Stefano Stabellini
> > > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > >> On Mon, 20 Jan 2014, Wu, Feng wrote:
> > >>> > -----Original Message-----
> > >>> > From: xen-devel-bounces@xxxxxxxxxxxxx
> > >>> > [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Shakeel Butt
> > >>> > Sent: Monday, January 20, 2014 1:48 PM
> > >>> > To: xen-devel@xxxxxxxxxxxxx
> > >>> > Subject: [Xen-devel] vga passthrough with qemu-xen (or qemu upstream)
> > >>> >
> > >>> > 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?
I never managed to get it working - it certainly isn't just a matter of
enabling the option. There is at least the matter of also side-loading
the VGA BIOS, and IIRC that was limited to 64KB in size, which rules
out all ATI and Nvidia GPUs of the past 2-3 generations.

Having said that - I never found a particularly good use-case for
primary passthrough. Once the GPU driver loads it works just the
same for all intents and purposes.

Gordan

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