Re: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough support

["Michael S. Tsirkin" <mst@xxxxxxxxxx>]

On Wed, Jul 02, 2014 at 03:15:02PM +0000, Ross Philipson wrote:
> > -----Original Message-----
> > From: Paolo Bonzini [mailto:pbonzini@xxxxxxxxxx]
> > Sent: Wednesday, July 02, 2014 7:33 AM
> > To: Ross Philipson; Michael S. Tsirkin; Stefano Stabellini
> > Cc: peter.maydell@xxxxxxxxxx; xen-devel@xxxxxxxxxxxxxxxxxxx; Allen M.
> > Kay; Kelly.Zytaruk@xxxxxxx; qemu-devel@xxxxxxxxxx;
> > yang.z.zhang@xxxxxxxxx; anthony@xxxxxxxxxxxxx; Anthony Perard; Chen,
> > Tiejun
> > Subject: Re: [Xen-devel] [v5][PATCH 0/5] xen: add Intel IGD passthrough
> > support
> > 
> > Il 01/07/2014 19:39, Ross Philipson ha scritto:
> > >
> > > We do IGD pass-through in our project (XenClient). The patches
> > > originally came from our project. We surface the same ISA bridge and
> > > have never had activation issues on any version of Widows from XP to
> > > Win8. We do not normally run server platforms so I can't say for sure
> > > there.
> > 
> > The problem is not activation, the problem is that the patches are
> > making assumptions on the driver and the firmware that might work today
> > but are IMHO just not sane.
> 
> Sure I don't think anybody is suggesting that activation is
> the main problem. It was just a potential problem with respect
> to one of the proposed solutions.
> 
> When we first started doing this (back in 2009ish) we ran into
> all these problems with surfacing ISA bridges, giving guest
> drivers access to registers in the host bridge. etc. Nothing seemed
> sane; I sympathize. 

At some level, maybe Paolo is right.  Ignore existing drivers and ask
intel developers to update their drivers to do something sane on
hypervisors, even if they do ugly things on real hardware.

A simple proposal since what I wrote earlier though apparently wasn't
very clear:

  Detect Xen subsystem vendor id on vga card.
  If there, avoid poking at chipset. Instead
        - use subsystem device # for card type
        - use second half of BAR0 of device
        - instead of access to pci host

hypervisors will simply take BAR0 and double it in size,
make second part map to what would be the pci host.

Tiejun, is there a chance this can be done not only
on Linux but on windows as well?


> > 
> > I would have no problem with a clean patchset that adds a new machine
> > type and doesn't touch code in "-M pc", but it looks like mst disagrees.
> >   Ultimately, if a patchset is too hacky for upstream, you can include
> > it in your downstream XenClient (and XenServer) QEMU branch.  It
> > happens.
> > 
> > Paolo
> > 
> > -----
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