Re: [Qemu-devel] [PATCH] Xen PCI passthrough: fix passthrough failure when irq map failure

[Zhao Yan <yan.y.zhao@intel.com>]

On Thu, Oct 18, 2018 at 03:56:36PM +0100, Roger Pau Monné wrote:
> On Thu, Oct 18, 2018 at 08:22:41AM +0000, Zhao, Yan Y wrote:
> > Hi
> > The background for this patch is that: for some pci device, even it's PCI_INTERRUPT_PIN is not 0, it actually does not support INTx mode, so we should just report error, disable INTx mode and continue the passthrough.
> > However, the commit 5a11d0f7 regards this as error condition and let qemu quit passthrough, which is too rigorous.
> > 
> > Error message is below:
> > libxl: error: libxl_qmp.c:287:qmp_handle_error_response: Domain 2:received an error message from QMP server: Mapping machine irq 0 to pirq -1 failed: Operation not permitted
> 
> I'm having issues figuring out what's happening here.
> s->real_device.irq is 0, yet the PCI config space read of
> PCI_INTERRUPT_PIN returns something different than 0.
> 
> AFAICT this is due to some kind of error in Linux, so that even when
> the device is supposed to have a valid IRQ the sysfs node it is set to
> 0, do you know the actual underlying cause of this?
> 
> Thanks, Roger.
Hi Roger
Sorry for the later reply, I just missed this mail...
On my side, it's because the hardware actually does not support INTx mode,
but its configuration space does not report PCI_INTERRUPT_PIN to 0. It's a
hardware bug, but previous version of qemu can tolerate it, switch to MSI
and make passthrough work.

Thanks
Yan