PIRQ handling and PVH dom0?

[Alex Olson <this.is.a0lson@xxxxxxxxx>]

I further attempted to see how far PVH dom0 can get but had a general question 
regarding what is not yet implemented... 

With an initial version of Roger's recent "vpci/msix: fix PBA access" patches 
and after refreshing his earlier 2018 patchset "vpci: add support for SR-IOV 
capability" regarding SR-IOV support for PVH dom0, I was able to get both 
physical functions and virtual functions of an SR-IOV network card to operate 
correctly in PVH dom0.

However, it looks like any PCI-passthrough for HVM domUs with PVH dom0 is not 
yet implemented. I see the "PHYSDEVOP_map_pirq" call fails since the 
"emulation_flags" for dom0 do not include "XEN_X86_EMU_USE_PIRQ"...

        libxl: error: libxl_pci.c:1461:pci_add_dm_done: Domain 
1:xc_physdev_map_pirq irq=17 (error=-1): Function not implemented               
                                                                                
                                                                                
                                                                                
                                          
        libxl: error: libxl_pci.c:1781:device_pci_add_done: Domain 
1:libxl__device_pci_add failed for PCI device 0:5:0.1 (rc -3)                   
                                                                                
                                                                                
                                                                                
                                      
        libxl: error: libxl_create.c:1895:domcreate_attach_devices: Domain 
1:unable to add pci devices                                              


What is PVH dom0 missing at a conceptual level for PCI passthrough to domUs?  I 
naively assumed that an HVM domU guest wouldn't care much whether dom0 was PV 
or PVH in terms of passthrough device IRQ handling...

Thanks

-Alex