We have a quirky PCI device which requires PCI write config access. We had modified /etc/xen/xend-pci-permissive.sxp and /etc/xen/xend-pci-quirks.sxp for Xen to give full access to PCI config space of our home grown PCI device.

Kindly let me know how we can do the same in KVM. I'm using virsh create <XML> method to create a HVM guest.