gfx card passthrough broken with latest head

gfx card passthrough broken with latest head

[André Weidemann]

Hi,
I pulled latest git yesterday and noticed that graphics card pass 
through does not work anymore. The VM hangs (probably when initializing 
the gfx card) when passing a graphics card to the VM.

I started to do a git bisect but device assignment does not work at all 
when doing it.

I started like this:

cd /usr/local/src
git clone git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git 
qemu-kvm-2011-08-12
cd qemu-kvm-2011-08-12
git bisect start
git bisect good fda19064e889d4419dd3dc69ca8e6e7a1535fdf5
git bisect bad 44755ea36fee3f0b1093ef27404def8857602274

Bisecting: 229 revisions left to test after this
[55c0975c5b358e948b9ae7bd7b07eff92508e756] Do constant folding for shift 
operations.

./configure --audio-drv-list=alsa --target-list=x86_64-softmmu 
--enable-kvm-device-assignment

ERROR: unknown option --enable-kvm-device-assignment

What am I doing wrong?

Regards
  André

Re: gfx card passthrough broken with latest head

[André Weidemann]

Hi,

On 13.08.2011 15:35, André Weidemann wrote:
> Hi,
> I pulled latest git yesterday and noticed that graphics card pass
> through does not work anymore. The VM hangs (probably when initializing
> the gfx card) when passing a graphics card to the VM.
>
> I started to do a git bisect but device assignment does not work at all
> when doing it.
>
> I started like this:
>
> cd /usr/local/src
> git clone git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git
> qemu-kvm-2011-08-12
> cd qemu-kvm-2011-08-12
> git bisect start
> git bisect good fda19064e889d4419dd3dc69ca8e6e7a1535fdf5
> git bisect bad 44755ea36fee3f0b1093ef27404def8857602274
>
> Bisecting: 229 revisions left to test after this
> [55c0975c5b358e948b9ae7bd7b07eff92508e756] Do constant folding for shift
> operations.
>
> ./configure --audio-drv-list=alsa --target-list=x86_64-softmmu
> --enable-kvm-device-assignment
>
> ERROR: unknown option --enable-kvm-device-assignment
>
> What am I doing wrong?

I continued with "git bisect bad" from this point on, but up to where I 
started, no revision supported device assignment.

I then did a "git bisect reset" and started over again. Now I continued 
with a few "git bisect good" until a revision came up that supported 
device assignment, but then after compiling and running 
qemu-system-x86_64, it exited with a segmentation fault. I continued 
with "git bisect good" until the end but all revision supporting device 
assignment existed with a segmentation fault.

How come so many revision do not support device assignment? Is there a 
trick to enable it?

Any help in this matter is greatly appreciated.

Regards
  André

Re: gfx card passthrough broken with latest head

[Chris Wright]

* André Weidemann (Andre.Weidemann@web.de) wrote:
<snip>
> >git clone git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git
<snip>
> >./configure --audio-drv-list=alsa --target-list=x86_64-softmmu
> >--enable-kvm-device-assignment
> >
> >ERROR: unknown option --enable-kvm-device-assignment
<snip>
> How come so many revision do not support device assignment? Is there
> a trick to enable it?

Bisection qemu-kvm userspace is tricky.  The upstream qemu repo
(git://git.qemu.org/qemu.git) does not have PCI device assignment
support.  The qemu-kvm repo does regular merges w/ the upstream qemu
repo.  As you bisect through the qemu-kvm repo history, you are likely
to land on a commit that is from upstream (meaning a tree w/out
downstream qemu-kvm additions, like device assignment).

Depending on where you suspect the issue is coming from, you can be
careful to bisect only through the qemu-kvm tree (by skipping back to a
merge point), or you can remerge the qemu-kvm tree to the qemu tree when
you bisect into the qemu tree.

Note...gfx assignment has many issues associated w/ it and often does
not work.  You can check out Allen Kay's presentation at the recent KVM
Forum for some examples: http://goo.gl/Hyk13

thanks,
-chris