Simon,
For the pass-through device's INTx emulation, we follow the policy: if 
virtual function 0, use INTA#, otherwise use hardware value. However, 
this policy only apply when bind_pt_pci_irq to xen, and always use 
physical value when exporting to guest. This discrepancy cause different 
INTx, thus different GSI in xen and guest, so that interrupts never got 
injected to guest. E.g. when assigning a USB controller with non-zero 
function(00:1d.2) to guest as 00:4.0, xen will see INTA#, while guest 
see INTC#.

This simple patch can fix it. Could you pls. review it?

Thanks,

-- 
best rgds,
edwin