[Pkg-xen-devel] Bug#776742: xen-utils-common: no support for VGA Passthrough

[Juergen Schinker]

can you add your hw specs and also what about Debian-Stretch?
J

----- On 12 Feb, 2017, at 18:05, Chuck Zmudzinski brchuckz at netscape.net wrote:

> This bug, at its core, is that currently there is no supported solution
> for VGA
> passthrough on Xen for stable version Jessie from Debian.
> 
> After browsing Xen's repositories, I found out that Xen did not claim to
> support
> VGA passthrough with the upstream qemu-xen device model until Sep 25,
> 2015, the
> date the xl.cfg man page was updated to indicate support for VGA passthrough
> with upstream qemu-xen. This change to the xl.cfg man page was only made
> on the
> Xen version 4.7 and 4.8 branches, so if you want to use VGA passthrough
> without
> the traditional qemu-dm binary, you must upgrade to at least Xen version
> 4.7.
> Debian testing (currently stretch) uses Xen 4.8 and it presumably
> supports VGA
> passthrough without qemu-xen-traditional but I have not tried it.
> 
> This situation leaves users of Debian stable (currently Jessie) with no
> supported solution from Debian for VGA passthrough on Xen. Obviously
> there are
> two solutions. Backport Xen 4.7 or greater to Jessie, or restore the
> traditional qemu-dm binary to the Xen 4.4.x package for Jessie.
> 
> A couple of months ago I decided to try and rebuild the Xen source package
> for Jessie with support for qemu-xen-traditional from upstream included.
> It did
> not take long to get a working package that solves this bug. I
> discovered the
> following facts:
> 
> 1. Adding qemu-xen-traditional in a way supported by Xen also requires
> rombios
>    which, like qemu-xen-traditional, is disabled in Debian's official
> build of
>    Xen for Jessie.
> 
> 2. After configuring the build for qemu-xen-traditional and rombios, the
> only
>    binary package that is modified significantly is xen-utils-4.4, which is
>    where the qemu-dm binary is installed, and where a modified
> hvmloader binary
>    is installed so it includes the statically linked rombios modules.
> 
> 3. With these changes to xen-utils-4.4, together with a few simple
> configuration
>    tweaks such as the location of the qemu keymaps directory, VGA
> passthrough
>    on Debian Jessie works with HVM domains that use qemu-xen-traditional,
>    and this feature can be enabled simply by adding 2 lines to the config
>    file: device_model_version = 'qemu-xen-traditional'
>          gfx_passthru = '1'
>    I think the second option is only needed if you want the passed through
>    video card to be the primary video adapter, but I have never tried VGA
>    passthrough as a secondary adapter in the HVM. Your mileage may vary.
> 
> 4. Also, with these changes to xen-utils, the qemu-xen upstream device model
>    and the seabios bios remain the defaults, so these changes will not do
>    violence to existing installations that use upstream qemu-xen and
> seabios.
> 
> 5. It is not possible to build the Xen source package with
> qemu-xen-traditional
>    in such a way that it meets all the requirements for inclusion in
> the main
>    area of Debian's archive of packages. Specifically, the build must
> access
>    remote repositories to download qemu-xen-traditional source files from
>    xen.org and ipxe source files from ipxe.org. Later I found it is
> possible to
>    build and configure a working package that supports VGA passthrough
> without
>    ipxe by making a couple of small configuration tweaks that remove
> etherboot
>    and ipxe support from the rombios modules that are statically linked
> into
>    hvmloader. But the requirement that the build not access the
> internet for
>    source files cannot be met unless the xen source package is modified
>    by adding another original source tar archive, something like the
>    xen_4.1.6.lts1.orig-qemu.tar.xz source file for the xen package for
> oldstable
>    Wheezy that does include support for qemu-xen-traditional and VGA
>    passthrough, in order for the build to succeed without needing to access
>    a remote repository.
> 
> With these discoveries, I would like to make the observation that
> although it is
> not trivial, it seems like it would not be too dificult for the Debian
> Xen team
> to add support for qemu-xen-traditional and rombios to the Xen source
> package so
> the resulting binary packages would support VGA passthrough when an HVM
> domain
> is configured to use qemu-xen-traditional.
> 
> After having said all this, the stage is set for my question: Why hasn't the
> Debian Xen team added support for VGA passthrough in Debian Jessie?
> 
> From Archived Bug #688311, Bastian Blank asserted that qemu-dm will not
> come
> back and that you have to use the normal (now called upstream) qemu.
> 
> Ian Campbell responded: "Just FYI position of upstream is that the
> 'traditional'
> qemu-dm will continue to be maintained for the foreseeable future for the
> benefit of users who are running guest OSes which are not as happy to
> have the
> "motherboard" changed from under them as Linux is."
> 
> That was over four years ago, and Debian still has not restored qemu-dm so
> users of a stable Debian system can have a working VGA Passthrough for any
> guest OS, not even Linux, much less users of those Oses that don't like the
> motherboard changed from other them.
> 
> As far as I can tell, Xen still maintains the traditional qemu-dm, and I was
> able to recently rebuild the xen package for Jessie and get VGA Passthrough
> working on Jessie with the most recent version of the traditional device
> model
> that is available from Xen for the stable 4.4 release of Xen.
> 
> So I ask again, why can't the Debian Xen team restore qemu-dm to its
> official
> Xen package for Jessie?
> 
> The only reasonable reasons I can think of is that there is some free
> software
> licensing issue with the rombios modules that are statically linked to
> hvmloader
> or with some necessary component of qemu-dm, or the Debian Xen team has
> too few
> resources and is devoting its efforts to developing Xen for stretch
> rather than
> adding feaatures that did not make it into Jessie when it was released.
> But why
> should oldstable Wheezy have a feature that stable Jessie does not have?
> 
> In any case, I hope the Debian Xen team can explain why qemu-dm cannot be
> restored to Debian Jessie's offical xen package.
> 
> Thank you for your consideration of my question.
> 
> Sincerely,
> 
> Chuck Zmudzinski