Re: [Xen-users] can't passthrough video card

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 10/27/2013 07:16 AM, bob evans wrote:
> Hi, I have been trying to find help with a problem I am having passing a video 
> card to a Xen domu. I do have VT-d enabled in BIOS and I can pass some PCI 
> cards to the domu, but trying to pass my video card results in an error. My 
> dom0 is Kubuntu 3.10, the video card I am trying to pass is a Radeon 7970 ghz. 
> I am using Xen version 4.3.0(preserve-AS), my motherboard is an Asrock Extreme4 
> z87, and my CPU is an Intel i7-4771.
>
> When I tried to run my HVM for the first time I had the error: "Error: pci: PCI 
> Backend  and pci-stub don't own device 0000:02:00.0"
>
> I found that I had to unbind my PCI devices from the Linux kernel drivers and 
> bind them to pciback. I found these instructions for doing this:
>
> echo 0000:08:00.0 > /sys/bus/pci/devices/0000:08:00.0/driver/unbind
> echo 0000:08:00.0 > /sys/bus/pci/drivers/pciback/new_slot
> echo 0000:08:00.0 > /sys/bus/pci/drivers/pciback/bind
>
> These commands worked great for PCI USB controller, I was able to passthrough 
> without any problems. When it was time to pass my video card I ran into 
> problems. Here is the relevant output of lspci -k
You need to do a few things:

1) Put something like this in your /etc/modprobe.d/xen-pciback.conf (or 
equivalent on your distro)
options xen-pciback hide=(08:00.0)(08:00.1)

where 08:00.0 and 08:00.1 are PCI IDs of the device in question.
Alternatively, you may need to do the equivalent of this on your kernel 
boot line if your xen-pciback module is built into the kernel.
If any of the devices were bound to a different driver first, for those 
devices it is easier to do something like:
xl pci-assignable-remove 0000:08.00.0

instead of what you did above.

> 02:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] 
> Tahiti XT [Radeon HD 7970/R9 280X]
>          Subsystem: Hightech Information System Ltd. Tahiti XT2 [Radeon HD 7970 
> GHz Edition]
>          Kernel driver in use: radeon
> 02:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti XT HDMI 
> Audio [Radeon HD 7970 Series]
>          Subsystem: Hightech Information System Ltd. Device aaa0
>          Kernel driver in use: snd_hda_intel
>
> I was able to unbind the VGA controller with this command: echo -n 0000:02:00.0 
> > /sys/bus/pci/drivers/radeon/unbind
> I couldn't get it to work with this command: echo 0000:02:00.0 > 
> /sys/bus/pci/devices/0000:02:00.0/driver/unbind
This is a problem - if the radeon driver has already initialized the 
card, it's not going to work. ATI cards' BIOS and drivers aren't good 
enough to handle this situation properly.
> This is ok though, because lspci -k now shows:
>
> 02:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] 
> Tahiti XT [Radeon HD 7970/R9 280X]
>          Subsystem: Hightech Information System Ltd. Tahiti XT2 [Radeon HD 7970 
> GHz Edition]
> 02:00.1 Audio device: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti XT HDMI 
> Audio [Radeon HD 7970 Series]
>          Subsystem: Hightech Information System Ltd. Device aaa0
>          Kernel driver in use: snd_hda_intel
>
> Now I run into the issue I am currently stuck at. When I issue the commands
>
> echo 0000:02:00.0 > /sys/bus/pci/drivers/pciback/new_slot
> echo 0000:02:00.0 > /sys/bus/pci/drivers/pciback/bind
>
> The first command works fine, but the second results in an error: -bash: echo: 
> write error: No such device
Use xl command as described above. It is simpler and less error prone.

Gordan

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