RE: [Xen-devel] Experimental results for VGA passthrough

[<djmagee@xxxxxxxxxxxx>]

The DQ45CB does not have enough PCI Express lanes to drive the IGD and a
x16 graphics card at the same time.
 
-----Original Message-----
From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
[mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Beng Heng,
Ng
Sent: Thursday, June 04, 2009 11:09 AM
To: xen-devel
Subject: [Xen-devel] Experimental results for VGA passthrough

Hi,

I tried patching Xen 3.4 Testing c/s 19628 with vga passthrough code
(less HID passthrough), and did some tests. I made some modifications in
pci_setup to skip loading the emulated VGA bios and pci_load_option_roms
to load the passthrough VGA bios. My setup uses Intel DQ45CB and ATI
HD2600XT.

The BDFs for the relevant devices are:
Intel IGD  00:02.0
ATI gfx    01:00.0, 01:00.1
There's 2 BDFs for ATI because one of them is for the Audio. Both have
to be passed through simultaneously.

In the first scenario, Intel IGD is set up as the primary for Dom0. The
ATI gfx is passed through to DomU. Interestingly, it is the screen that
is connected to Intel's output that displays DomU (albeit with few
colors and low resolution). However, in the Device Manager, ATI is
reported. I believe this is because Intel's address space is being
mapped, instead of ATI's. Shutting down DomU does not return the display
to Dom0. The display remains at the last screen showing DomU shutting
down. Except for the shutting down phase, I've recorded the observations
in the first attachment.

In the second scenario, Intel IGD is passed through to DomU. The ATI gfx
is thus absent. However, when DomU is booted, there is an IOMMU page
fault. This is shown in the second attachment starting from Line 659.
The system subsequently hangs. Does anyone have an explanation to what's
going on in this case?

So, VGA passthrough works, but seems extremely flaky. Any
comments/suggestions to correct the problems observed will be greatly
appreciated.

Thanks.

- Beng Heng


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