Re: [Xen-devel] [PATCH] hvmloader: Intel GPU passthrough, reverse OpRegion

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 24 Nov 2011, Jean Guyader wrote:
> On 24/11 11:18, Stefano Stabellini wrote:
> > On Wed, 23 Nov 2011, Jean Guyader wrote:
> > > On 23 November 2011 17:28, Jean Guyader <jean.guyader@xxxxxxxxx> wrote:
> > > > On 23 November 2011 17:20, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> > > >> On 23/11/2011 16:07, "Jean Guyader" <jean.guyader@xxxxxxxxxxxxx> wrote:
> > > >>
> > > >>>
> > > >>> The Intel GPU uses a two pages NVS region called OpRegion.
> > > >>> In order to get full support for the driver in the guest
> > > >>> we need to map this region.
> > > >>>
> > > >>> This patch reserves 2 pages on the top of the RAM and
> > > >>> mark this region as NVS in the e820. Then we write the
> > > >>> address to the config space (offset 0xfc) so the device
> > > >>> model can map the OpRegion at this address in the guest.
> > > >>
> > > >> Please use mem_hole_alloc() rather than adjusting {low,high}_mem_pgend.
> > > >>
> > > >
> > > > Ok, that is handy.
> > > >
> > > >> Is it correct to do this for *all* gfx devices with Intel vendor id?
> > > >>
> > > >
> > > > The OpRegion is a Intel GPU specific thing.
> > > >
> > > 
> > > Sorry didn't read carefully the first time, yes I think it's correct
> > > to do that for
> > > all the Intel GPU. Maybe I can do a read on 0xfc first to check if I 
> > > don't get
> > > something dodgy like 0xfffffff or 0. I could also double check in Qemu 
> > > that it's
> > > a NVS region on the host, but that won't work for stub domain.
> > 
> > access to physical memory through /dev/mem should work from the stubdom
> 
> I would think that /dev/mem in a stubdom will expose the memory of the guest 
> but
> maybe I'm wrong.
> 
 
Nope, it maps host memory. Of course you need to make sure you have
given enough privileges to the stubdom so that it can actually map the
memory area.

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