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

On Wed, Jul 02, 2014 at 01:33:09PM +0200, Paolo Bonzini wrote:
> 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.
> 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.

And then this discussion will come back again in a year when folks
rebase and ask: Why hasn't this been done upstream.

Then the discussion resumes ..

With this long thread I lost a bit context about the challenges
that exists. But let me try summarizing it here - which will hopefully
get some consensus.

1). Fix IGD hardware to not use Southbridge magic addresses.
    We can moan and moan but I doubt it is going to change.

2). Since we need the Southbridge magic addresses, we can expose
    an bridge. [I think everybody agrees that we need to do
    that since 1) is no go).

3). What kind of bridge. We can do:

     a) Two bridges - one 'passthrough' and the legacy ISA bridge
        that QEMU emulates. Both Linux and Windows are OK with
        two bridges (even thought it is pretty weird).

     b) One bridge - the one that QEMU emulates - and lets emulate
        more of the registers (by emulate - I mean for some get the
        data from the real hardware).

           b1). We can't use the legacy because the registers are
                above 256 (is that correct? Did I miss something?)

           b2)  We would need to use the Q35.
                b2a). If we need Q35, that needs to be exposed in
                      for Xen guests. That means exposing the 
                      MMCONFIG and restructing the E820 to fit that
                        - Migration is not working with Q35.
                          (But for v1 you wouldn't migrate, however
                           later hardware will surely have SR-IOV so
                           we will need to migrate).

                        - There are no developers who have an OK
                          from their management to focus on this.
                           (Potential solution: Poke Intel management to see
                            if they can get more developers on it)

4). Code does a bit of sysfs that could use some refacturing with
    the KVM code.
    Problem: More time needed to do the code restructing.

Is that about correct?

What are folks timezones and the best days next week to talk about
this on either Google Hangout or the phone?

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