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Re: [Xen-users] USB pci passthrough, also iommu groups

Hi Jo,

thanks for the response. I probably should have said - it does work if you use KVM, so it's not the hardware. The 'interesting' quirk in passing through USB, though, is that you can pass through only in two groups of four ports and one port, rather than something more equal.

In your two NIC case, however - it might be. Xen does not seem to identify iommu groups. This is an issue on the S3210 chipset which is too old to have ACS protection (the expansion cards on the same segment can talk to each other without IOMMU protection, which is a problem if they're not assigned to the same VM).

Unfortunately the S3210 is not very friendly in this regard. All of the PCI slots are on the same segment, and in the same IOMMU group, as is the second built in NIC, which hangs off a PCI-X bridge. The other NIC is supposed to be on a different segment according to the manual and this tallies with my memory.

The specification does lie, however. I'm pretty certain that the system put the embedded Matrox G200e and one of the PCIe slots (the x8 one, hanging off the MCH, IIRC) in the same IOMMU group, when the G200e is supposed to be attached to the ICH instead.

In my case I'm not taking chances - all Âdevices in a PCI slot including the second embedded NIC are passed through to the same VM.

I don't mind this board too much, as I think the hardware is broadly functional, but the 1x transfer limit for VGA cards in the 16x/8x slots rankles somewhat, and the fact that Intel were lazy enough to keep the audio functionality from the X38 chipset present but uninitialised, results in it hanging Linux every few dozen boots.. Would it have hurt to disable it properly, or enable it and stick on some speaker connectors?


On 27 August 2014 14:32, Jo Mills <jo@xxxxxxxxxxxxxxxx> wrote:
On Wed, Aug 27, 2014 at 10:17:32AM +0100, Peter Kay wrote:
> I have pci passthrough working on my SH3210 motherboard for a VGA
> card, sound card, firewire and LAN. Unfortunately when I pass through
> the USB controllers and the VM boots, it hard resets the entire
> machine. Is anyone else experiencing problems, before I report this
> as a bug? Happens on unpatched 4.4 and -unstable
> I can work round this on 4.4 with host device passthrough (although
> this seems not to work in -unstable, currently?) But I'd prefer the
> whole controller.
> Also, where are iommu groups shown in Xen? There doesn't seem to be
> any enforcement of having go pass through an entire group of devices
> that aren't protected by ACS.

Hi Peter,

Please excuse me if this is a bit wide of the mark, but I spent ages
and ages trying to get two PCI network cards passed through on the
following hardware:

  Hardware: ÂIntel S3200SHV motherboard
  BIOS  : ÂS3200X38.86B.00.00.0052
  CPU  Â: ÂIntel Core 2 (quad)

It was all OK until I tried to start a VM using the second passed
through NIC at which point everything fell over. Xen-devel got
involved but in the end I just ran out time to try and solve it and
had to get on with my life ;-)Â So maybe it's the hardware?

Good luck,


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