@roxie yeah
open /etc/mkinitcpio.conf
add to MODULES (inside the parentheses): vfio_pci vfio vfio_iommu_type1 vfio_virqfd
go to /etc/modprobe.d/vfio.conf (or wherever you have this configured)
ensure there is a line like
options vfio-pci ids=aaaa:bbbb,cccc:dddd...
then do
sudo mkinitcpio -P