Hi everybody.
For begin, congratulation for your excellent jobs...
xen work fine on my main server.
But I would to push with vga passtrough,
with an dell laptop latitude E6520.
modprobe pci-stub

echo "10de 1056" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:01:00.0" > /sys/bus/pci/devices/0000\:01\:00.0/driver/unbind
echo "0000:01:00.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "10de 0e08" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:01:00.1" > /sys/bus/pci/devices/0000\:01\:00.1/driver/unbind
echo "0000:01:00.1" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c26" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1d.0" > /sys/bus/pci/devices/0000\:00\:1d.0/driver/unbind
echo "0000:00:1d.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c2d" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1a.0" > /sys/bus/pci/devices/0000\:00\:1a.0/driver/unbind
echo "0000:00:1a.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c20" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1b.0" > /sys/bus/pci/devices/0000\:00\:1b.0/driver/unbind
echo "0000:00:1b.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "14e4 4727" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:03:00.0" > /sys/bus/pci/devices/0000\:03\:00.0/driver/unbind
echo "0000:03:00.0" > /sys/bus/pci/drivers/pci-stub/bind

here all was right, juste 01:00.0 and 01:00.1 doesn't work
for have screen given to domU....
for search little more, I have try (PCI express):
echo "8086 1c10" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1c.0" > /sys/bus/pci/devices/0000\:00\:1c.0/driver/unbind
echo "0000:00:1c.0" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c12" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1c.1" > /sys/bus/pci/devices/0000\:00\:1c.1/driver/unbind
echo "0000:00:1c.1" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c14" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1c.2" > /sys/bus/pci/devices/0000\:00\:1c.2/driver/unbind
echo "0000:00:1c.2" > /sys/bus/pci/drivers/pci-stub/bind
echo "8086 1c16" > /sys/bus/pci/drivers/pci-stub/new_id
echo "0000:00:1c.3" > /sys/bus/pci/devices/0000\:00\:1c.3/driver/unbind
echo "0000:00:1c.3" > /sys/bus/pci/drivers/pci-stub/bind

with Xen 4.4 and last linux kernel from :
git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git

that was good until 10-15minutes,
when an moment, .... shutdown...
and never can reboot.
no bios access, sadly, I thing the laptop is dead.

I'm so sorry, I can have more information about kernel conf,
just not forgetten with in begin the last debian installation server.7

thanks for heard me.
good luck and fine jobs.