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[Xen-users] VGA Passthrough & PCIBack inquiry

  • To: xen-users@xxxxxxxxxxxxx
  • From: Casey DeLorme <cdelorme@xxxxxxxxx>
  • Date: Wed, 7 Mar 2012 17:58:17 -0500
  • Delivery-date: Wed, 07 Mar 2012 23:00:04 +0000
  • List-id: Xen user discussion <xen-users.lists.xen.org>


Testing VGA Passthrough, and need some tips.

I am running Debian Wheezy with a Custom Linux Kernel 3.2.9, and have compiled pciback into the kernel.

I have successfully grabbed devices with pciback.

Running xm pci-list-assignable-devices shows me the devices, and I have successfully passed onboard HD Audio & USB 3.0 controllers, and tested them successfully in a Windows 7 HVM.

Problem #1:

I don't get any messages in dmesg about seized devices.

Problem #2:

GPU is sitting behind a NF200 chip, which doesn't have ACS, and so I get the following error:

Error: pci: to avoid potential security issue, 0000:03:00.0 is not allowed to be assigned to guest since it is behind PCIe switch that does not support or enable ACS.

Problem #3:

I tried plugging the card into a separate PCIe Slot not behind the NF200 chip, but it was sitting behind a layer attached to several other devices, including the network adapters.

Suddenly, no eth0 (no internet), and a long list of devices from the xm command.

I removed the xen-pciback.hide line from the grub, and rebooted.  The devices are still being taken hostage and unavailable to the Dom0 host.  When I boot into the normal Linux Kernel it has working internet again, so something in Xen must need a modification.

So, my questions are:

Why doesn't dmesg show me any pciback messages?  Is it because I'm not using a module?

Is there a way to ignore the ACS security problem?  I read about flags in the xend-config, but don't know if anyone has tested them on Xen 4.1.2:
> pci-passthrough-strict-check no
> pci-dev-assign-strict-check no

Also, since Xen is moving to the xl toolstack, does it still use the xend-config file?  If not, what is the xl alternative?

Also, how can I reset devices taken by pciback and rebind them to Dom0?  Is there a xen-pciback.unhide option, or a reset command?  Given that the regular Linux kernel boots, I want to think that something was changed in the Xen config that I need to reset someplace.

If anyone has any ideas, please let me know, for now I'm moving onto installation 49 and going to give those flags a try.

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