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

[Roger Pau Monné]

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.