@ajpri1998
Thank you so much, I've been beating my head against this all day.

I am trying to pass-through a dual NIC ethernet card. I turned VT-d on in the BIOS and ran

# /opt/xensource/libexec/xen-cmdline --set-dom0 "xen-pciback.hide(0000:03:00.0)(0000:03:00.1)" 

and rebooted, but they don't show up in the "xl pci-assignable-list" and still show the normal kernel driver being loaded for the card in dmesg

dmesg output