PCI devices on PCI to PCI bridges stopped being accessable from Xen with QEMU 2.3.0

The change set:

commit 3996e85c1822e05c50250f8d2d1e57b6bea1229d
Author: Paul Durrant <email address hidden>
Date:   Tue Jan 20 11:06:19 2015 +0000

    Xen: Use the ioreq-server API when available
...

Added calls to xen_map_pcidev()  when available.  However these call are only done at startup, not when the guest configures the PCI to PCI bridge.  So Xen 4.5.0 (which has these) using a QEMU 2.3.0 or later can no longer access PCI devices that are not on a root bridge.