dotfiles/example/microvm/pci-devices.nix

{
  config,
  lib,
  pkgs,
  ...
}:

let
  pciDevices = builtins.filter ({ bus, ... }: bus == "pci") config.microvm.devices;

  # TODO: don't hardcode but obtain from host config
  user = "microvm";
  group = "kvm";

in
{
  microvm.binScripts.pci-setup = lib.mkIf (pciDevices != [ ]) (
    ''
      set -eou pipefail
      ${pkgs.kmod}/bin/modprobe vfio-pci
    ''
    + lib.concatMapStrings (
      { path, ... }:
      ''
        cd /sys/bus/pci/devices/${path}
        if [ -e driver ]; then
          echo ${path} > driver/unbind
        fi
        echo vfio-pci > driver_override
        echo ${path} > /sys/bus/pci/drivers_probe
      ''
      +
        # In order to access the vfio dev the permissions must be set
        # for the user/group running the VMM later.
        #
        # Insprired by https://www.kernel.org/doc/html/next/driver-api/vfio.html#vfio-usage-example
        #
        # assert we could get the IOMMU group number (=: name of VFIO dev)
        ''
          [[ -e iommu_group ]] || exit 1
          VFIO_DEV=$(basename $(readlink iommu_group))
          echo "Making VFIO device $VFIO_DEV accessible for user"
          chown ${user}:${group} /dev/vfio/$VFIO_DEV
        ''
    ) pciDevices
  );
}