Re: [Xen-devel] PCI passthrough w/ shared IRQ in xen/master

[Michael D Labriola <mlabriol@xxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 02/19/2010 11:15:21 AM:

> > Is this a bug in something (kernel or hypervisor) or a known 
limitation
> > with pci passthrough...  I sure hope it's a bug, cause I need to fill 
all
> > my PCI slots with cards that are going to get passed into different
> > domUs...  :-/
> 
> I'm also very curious if this will be resolved at some point, so far 
I've
> run into similar problems using both 3.4-testing as well as 4.0.
> 
> When you do passthrough the device which has a shared IRQ, the domU will
> load the appropriate driver, but Xen refuses to assign the IRQ to the
> domU.
> In your case (and mine as well), the driver in domU is not aware that it
> has no IRQ, and thus starts generating interupts which are then caught 
by
> Dom0 as spurious interrupts, in my case even causing Dom0 to crash at
> times.

This actually sounds like 2 bugs when you describe it like that:

1. Can't assign shared IRQ PCI device to domU

2. Dom0 commit suicide when it gets spurious interrupts from a shared IRQ.

> 
> My way around this, is to try and move the other device IRQs out of the
> way (the ones that matter seem to be MSI capable), but i understand 
that's
> not always possible.
> If your other device is PCI based, and has no MSI, then for now I'm
> affraid you're out of luck...

The IRQ in question is shared with these devices (along with my NIC):

USB Controller
IDE Interface
FireWire

I don't really know what MSI is...  I'm assuming I'm out of luck, though.

> 
> Like you, I do hope this is considered a bug that will be fixed in a 
later
> release... anyone know what the xen policy is on this?

Well, if somebody wants to help with the kernel code, I can test it.

-Mike

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