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Re: [Xen-users] ATI VGA Passthrough / Xen 4.2 / Linux 3.8.10

On 05/09/2013 05:31 AM, Andrew Bobulsky wrote:
Hello Gordan,

A couple suggestions and questions for you!

Any suggestions gladly accepted. :)

The only two things that come to mind as possible causes are:
1) I'm on a dual socket system (dual Xeon X5650)

There's a thread on xen-devel right now.... Someone attempting iommu
with a dual socket Xeon system having trouble... Devices showing up
twice with different addresses.  It might not help at all, but it
could be worth a peek.

Do you have a thread name or archive link? I just signed up to the xen-devel list and had a quick look through the archives but haven't seen an obviously titled thread.

2) My motherboard's PCIe slots are behind NF200 PCIe bridges (yes, EVGA have 
decided in their infinite wisdom to put all 7 PCIe slots behind NF200s, none 
are directly attached to the Intel NB).

I'm so sorry :P. NF200 has probably caused a lot of xen tinkerers to
utter a few dozen cuss words a piece.

I can believe that. What is the solution, though?

The thing that drives me really nuts about the issues I'm seeing (which may or may not be specifically related to the NF200) is that it is so intermittent. It works well enough to boot up and work with a gaming type load for a few minutes. Then something happens that causes the VGA card to require a reset, and it all falls apart.

What about with PCIe devices behind NF200 bridges? I know the NF200s don't 
support PCI ACS, but that is a security feature (which I have disabled 
enforcement of to get this far), and AFAIK shouldn't actually affect the basic 
PCI passthrough capability.

Question: how'd you disable ACS?  I think it may be causing me some issues.


(pci-passthrough-strict-check no)
(pci-dev-assign-strict-check no)

in /etc/xen/xend-config.sxp

If it was causing you issues, however, I'd expect you to find errors in logs pointing at it.

Have you tried passing the NF200 bridge itself, along with the devices
behind it?  If its possible, it may enable a "cleaner" interaction as
the pcie bus ahead of it should be more well behaved.

I think I tried it, and the error I got back was that you can pass individual PCI devices, but not a PCI bridges.

All in all - rather deflating. I was really hoping that I wouldn't have to be 
stuck with rebooting between OS-es for another hardware generation.

Also, are you doing VGA pass through, or just pcie pass through of a
device that happens to be a video card?  I'm guessing you mean the
latter, but if not, it's definitely the more compatible option :)

I am doing the latter (secondary VGA passthrough). The packages / tools stack when combined with libvirt and virt-manager causes the VM configuration to end up in xenstore, and I have not yet figured out a clean way to migrate between a text config file and xenstore. I might try gfx_passthrough=1 once I've figured out how to toggle it in the xenstore configuration.


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