This hook require new device nodes to appear in /dev. If devtmpfs is
used, it's not a problem ("simple" initramfs case), but otherwise udevd
is needed - and it isn't running in pre-udev hook yet.
QubesOS/qubes-issues#2577
When PV Grub will be used, VM initramfs should not contain /lib/modules
mounting code, as the VM root.img will already contains kernel modules.
Make it possible by splitting the module.
QubesOS/qubes-issues#1354