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

On 07/01/2014 01:02 PM, Michael S. Tsirkin wrote:
On Tue, Jul 01, 2014 at 05:47:39PM +0100, Stefano Stabellini wrote:
On Tue, 1 Jul 2014, Michael S. Tsirkin wrote:
On Mon, Jun 30, 2014 at 03:31:05PM -0400, Ross Philipson wrote:
On 06/30/2014 03:22 PM, Stefano Stabellini wrote:
On Mon, 30 Jun 2014, Michael S. Tsirkin wrote:
On Mon, Jun 30, 2014 at 03:24:58PM +0800, Chen, Tiejun wrote:
On 2014/6/30 14:48, Michael S. Tsirkin wrote:
On Mon, Jun 30, 2014 at 10:51:49AM +0800, Chen, Tiejun wrote:
On 2014/6/26 18:03, 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

As I mentioned previously, the IGD guy told me we have no any unused a
offset or BAR in the config space.

And guy who are responsible for the native driver seems not be accept to
extend some magic offset of an existing MMIO BAR.

In addition I think in a short time its not possible to migrate i440fx to
q35 as a PCIe machine of xen.

That seems like a weak motivation.  I don't see a need to get something
merged upstream in a short time: this seems sure to miss 2.1,
so you have the time to make it architecturally sound.
"Making existing guests work" would be a better motivation.


So focus on this then. Existing guests will probably work
fine on a newer chipset - likely better than on i440fx.
xen management tools need to do some work to support this?

Unfortunately existing Windows guests don't take well chipset changes.
Windows might request a new activation.

That is a very good point. A while back I did a bunch of work to try to keep
Windows activated between running an instance of Windows on bare metal and
as a VM. There were numerous bits of hardware and firmware that went into
the calculation as to whether Windows thought it was the same platform for
activation purposes. Changing the chipset sounds like a likely candidate for
inspection. Somewhere out there on the webs is a partial list of the things
that are inspected - lost the URL.

It's not hard to try it out with kvm (you just need to remember to use ide with
q35: ahci is the default there).  I did, and windows did not ask me to

The detailed info is not hard to find:
links to:

Display Adapter
00010 (5)
SCSI Adapter
00011 (5)
IDE Adapter
0011 (4)
Network Adapter MAC Address
1001011000 (10)
RAM Amount Range (i.e. 0-64mb, 64-128mb, etc)
101 (3)
Processor Type
011 (3)
Processor Serial Number
000000 (6)
Hard Drive Device
1101100 (7)
Hard Drive Volume Serial Number
1001000001 (10)
010111 (6)
0 (1)
Hardware Hash version (version of algorithm used)
001 (3)

So no, chipset version won't cause re-activation.

The page you linked is about Windows XP. Newer Windows versions have
stricter activation rules.  I don't think that moving existing VM images
from piix to q35 could be done without extensive testing of all the
major existing operating system images. I certainly wouldn't rely on a
wikipedia page for this.

So do the testing then.
You don't even need to do anything on xen - run them all on kvm.
This testing will benefit everyone.

BTW is there a chance that adding the ISA bridge or doing other
tricks that Tiejun's patches do, will trigger windows activation?
Looks like this logic can cut both ways.

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.

Also I don't like the idea of tying Tiejun's patch series, that covers a
very narrow use case, to something as important and general purpose as
upgrading chipset.

If it's true that implementing igd passthrough on top of q35 is much
cleaner architecturally, then I don't see why we should merge a stop-gap
solution that we'll need to then support indefinitely.

We are talking about upstreaming functionality that xen already has, right?
So there's no time to market concern, whoever wants a solution today
has it.  Why not do it in the cleanest possible way?

Ross Philipson

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