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Re: [Xen-devel] Does xen-4.2.0 support VGA passthrough with the virtual machine created by xl command?

On Nov 13, 10:02am, Ian Campbell wrote:
} Subject: Re: [Xen-devel] Does xen-4.2.0 support VGA passthrough with the v

Good afternoon, hope the week is going well for everyone.

> On Tue, 2012-11-13 at 06:30 +0000, Qian Hu wrote:
> > With spice tool, I have to create a VM by xl command, and now I am
> > wondering if it supports VGA passghrouth?

> This list is for the development of Xen. You';d probably have more
> luck with these sorts of support requests on the xen-users list.

That would normally be the case but I'm suspicious there are issues
with VGA passthrough in 4.2.0.

I worked through all the vagaries of getting VGA passthrough going
with ATI cards about two years ago using the patches which are
available through the xen-vel archives.  We have run literally
thousands of Windows 7 passthrough sessions since then under 4.0.x and

We've just started validating 4.2.0 and passthrough reliably generates
segmentation faults in qemu-dm on the first attempt to do an I/O port
read.  The fault occurs with an identical configuration file using
either xm or xl.  Testing is being done with a 3.4.18 dom0 kernel.

I'm thinking we may have initially hit this in 4.1.0.  Segmentation
faults in the device emulator were being experienced but these seemed
to go away when we the dom0 kernel was switched back to a 2.6.32.x
kernel which we were using from Jeremy's GIT tree.

We need to make the jump to 3.4.x so I'm going to see if I can hunt
the issue down.

For those who may want to assist in trying to get all of this working
a bit better I have a 4.2.0 port of the ATI patches available at the
following location:


You will minimally need the qemu-dm binary from a build with this
patch applied.

I have also made available a helper script which we use to automate
the binding/rebinding of the VGA card and the USB controller passed
through to provide mouse/keyboard support.   The script can be picked
up from the following location:


The script is straight forward but will need a bit of tweaking for
items such as the PCI configuration being passwed through.

The script uses vbetool to issue a VGA post reset after the passthough
session is completed.  We run all this from a VGA text mode console
(yes we are old fashioned) so the results are 'unspecified' for trying
do this from anything resembling a remotely sophisticated graphics

This all tends to not be for the faint of heart.  I recommend having a
network login session running from a separate machine in case things
decide to go south.  A 'sync && reboot' always being a bit more
palatable then yanking the power cord.

The VGA cards we have been using were some monstrous thing which was
in vogue 2-3 years ago.  The fundamentals are as follows:

01:00.0 VGA compatible controller: ATI Technologies Inc Device 6898
(prog-if 00
[VGA controller])
        Subsystem: ASUSTeK Computer Inc. Device 0346
        Flags: fast devsel, IRQ 16
        Memory at b0000000 (64-bit, prefetchable) [size=256M]
        Memory at c1a00000 (64-bit, non-prefetchable) [size=128K]
        I/O ports at 3000 [size=256]
        Expansion ROM at c1a40000 [disabled] [size=128K]
        Capabilities: <access denied>

I will continue to hunt to see if I can further isolate the problem.
If anyone else wants to experiment a bit please do so and let me know
the results from 4.2.0.

For the record we are using Intel S3420GP motherboards.  We found the
VT-D implementation to be solid on that motherboard.

> Ian.

Hope the above is helpful.

Have a good evening.


}-- End of excerpt from Ian Campbell

As always,
Dr. G.W. Wettstein, Ph.D.   Enjellic Systems Development, LLC.
4206 N. 19th Ave.           Specializing in information infra-structure
Fargo, ND  58102            development.
PH: 701-281-1686
FAX: 701-281-3949           EMAIL: greg@xxxxxxxxxxxx
"We have more to fear from the bungling of the incompetent than from
 the machinations of the wicked."
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