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

Il 26/06/2014 13:26, Michael S. Tsirkin ha scritto:
On Thu, Jun 26, 2014 at 12:03:58PM +0200, Paolo Bonzini wrote:
Il 26/06/2014 11:18, Chen, Tiejun ha scritto:

- offsets 0x0000..0x0fff map to configuration space of the host MCH

Are you saying the config space in the video device?

No, I am saying in a new BAR, or at some magic offset of an existing MMIO


I think v5 goes a bit overboard and overrides too many registers,
driver likely needs much less.

But IMHO retro-fitting this into PIIX is where the problem is.
We could invent 1000 ways to do this, all of varying levels of

But why don't we start by more or less cleanly emulating what the driver
needs?  If we start with Q35 - it shouldn't be hard to tweak it's MCH to
add the necessary config space, right?

I know xen doesn't support q35 now but it's opensource :)

I think that's a good step 1. We can do PV hacks on top if we
decide they aren't too painful.

I don't think it's a PV hack. It should be this way in real hardware too (not exactly _this_ hack, but at least no improper relationship among IGD/MCH/PCH).

Once you add nested virtualization and nested device assignment to the mix, hacking subsystem IDs simply does not scale.


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