[fedora-virt] No iommu_group links in /sys/bus/pci/devices/

[Alex Williamson]

On Thu, 2013-06-27 at 17:42 +0200, Mario Ceresa wrote:
> Thanks Alex for your prompt reply! I'll gather all the information you
> requested, make some more tests with command line qemu and then write back.
> In the meantime, I'll briefly comment on same of your lines:
> 
> > Looks like you're still trying to create an SDL window since I believe
> that's on by default, add -nographic
> 
> I'll try that. However, I thought that the purpose of this line (in the
> arch tutorial at [1]) was to show a running VM with seabios. How can I see
> what's going on in the VM with no graphic?

It should initialize the VGA device and you should get a seabios splash
there (though depending on the card, it may already be gone by the time
the monitor wakes up).

BTW, see this message for some tips I learned setting this up:
 http://lists.nongnu.org/archive/html/qemu-devel/2013-05/msg01172.html

> > Not good.  This is using the vfio-vga-reset branches?
> 
> No. I'm just using the fedora-virt-preview repository [2]. I would like to
> test that branch. Is it:
> 
> git://github.com/awilliam/linux-vfio.git
> git://github.com/awilliam/qemu-vfio.git
> 
> with vfio-vga-reset, right?

Yes.  Current upstream/fedora-virt-preview is missing some things, like
the bus reset that is both the key to making it more reproducible and
the thorn that's keeping it from upstream.

> * Are there any recommended build options apart of:
> 
> CONFIG_VFIO_IOMMU_TYPE1=y
> CONFIG_VFIO=y
> CONFIG_VFIO_PCI=y
> CONFIG_VFIO_PCI_VGA=y

That's it.  I tend to run with a pretty lean host config, so you may
still run into problems with unbinding host drivers like radeon,
nouveau, nvidia.  Some of them are not very robust in their unbind code
so you need to blacklist them to avoid them altogether.

> * This is not the version in fedora-virt-preview repo so I need to
> recompile qemu as well, right?

Correct

> * Should I stop using the virt-preview repo completely? It also ships
> libvirtd and seabios packages I think...

For this, yes.  It's still in development upstream.

> > Cayman, is this a Radeon HD 6xxx [...] retrieving the BIOS from the
> device?
> 
> It is a radeon HD 7850. I would say there are no rom-related failures on
> dmesg but I'll check it again and report.

I should have known that, I have one of those ;)

> > Remove or patch them for what?
> 
> I have two gpu: nvidia quadro 4000 which is the primary and the radeon
> which is the one to pass through. I read in [3, 4] that someone needed to
> patch the nvidia binary driver. I can also get rid of that and nouveau
> altogether, but then, how can I check what the VM is doing without X?

Oh right, yes.  IIRC, the nvidia driver uses the VGA arbiter
incorrectly, acquiring the VGA lock and never releasing it.  That means
a guest hangs on the first attempt to try to use VGA space.  Yes, if you
intend to continue using the nvidia binary in the host, you'll need to
patch it.  Thanks,

Alex