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Re: [Xen-devel] Strange PCI Passthrough problem

  • To: "Cui, Dexuan" <dexuan.cui@xxxxxxxxx>
  • From: "Todd Deshane" <deshantm@xxxxxxxxx>
  • Date: Tue, 14 Oct 2008 19:16:38 -0400
  • Cc: xen-devel mailing list <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Delivery-date: Tue, 14 Oct 2008 16:17:03 -0700
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2008/10/10 Cui, Dexuan <dexuan.cui@xxxxxxxxx>:
> Hi Todd,
> According to the logs, we can see the 03:00.0 and 03:02.0 are behind the same 
> bridge, and both PCI devices lack the proper standard FLR capabilities.
> So currently in xend, the policy under this situation (sure, this limit is 
> not nice...) is:
> we can choose to assign both devices to the same guest;
> or,
> we can assign either device to a guest and the other becomes un-assignable 
> temporarily for another guest.

I applied the patch and was able to assign both device to the same guest fine.

> For the long run, should we add a bool parameter, like 'pci_force_assign', in 
> guest config file? If the end user sets the paramter to true, under such a 
> situation, if needed, we ignore the current policy and try to use the unsafe 
> D-state method (if available) to do FLR?

After applying the patch, I needed to hide the second card on the PCI
bridge and then restart
dom0, late binding could be used, but doesn't the pci_force_assign
need to apply to dom0/xend
and not the domU guest config?

xm pci-list-assignable-devices (after applying the patch), showed the
two 03: device on the same
line, which implied that they should be used on the same guest, but
maybe this could be made
more explicit?

I think that the limitation of assigning the devices to the same domU
is acceptable in many cases
and should somehow be enabled out of the box. Even if you need to
specify that it should happen
with a xend config option etc.


> Comments are welcome.
> Thanks,
> -- Dexuan
> ________________________________

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