Re: Xen interrupts when using passthrough

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 04/10/11 17:29, Eli Cohen wrote:
> Hi,
> I am trying to debug a problem where a guest does not receive the
> correct interrupt. It's a passtrough system where the guest is given a
> virtual function and is using MSIX to recieve the interrupts.

Do you mean that it is receiving interrupts for another device, or are
you trying to pass through multiple interrupts for a device and the
interrupt is appearing in the wrong event channel?

Could you describe your hardware setup in detail please, especially
AMD/Intel, IOMMU features in use according to Xen, and the PCI topology
of the box.

>  I am
> trying to understand how is the guest supposed to recieve the
> interrupt: Is it handled by dom0 which is using event channels to pass
> the interrupt to domU, or is handled directly by domU. Please send
> pointers to the code.

(I am not very familiar with guest IRQs so the following might not be
accurate)

For a PCI passthrough system, the interrupts should be bound directly to
domU, with no dom0 interaction.  A PIRQ is bound to an event channel
using the EVTCHNOP_bind_pirq in common/event_channel.c, which should be
set up by qemu for the relevant domU, when it is interpreting the PCI
config space reads/writes.

> Thanks in advance,
> eli;
>
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-- 
Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer
T: +44 (0)1223 225 900, http://www.citrix.com