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

[Jean Guyader <jean.guyader@xxxxxxxxxxxxx>]

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.

Jean

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