vfio fuckery

based on https://astrid.tech/2022/09/22/0/nixos-gpu-vfio/

nix/london/configuration.nix

@@ -4,8 +4,11 @@
   imports =
     [
       ./hardware-configuration.nix
+      ./vfio.nix
     ];
 
+  vfio.enable = true;
+
   # Bootloader
   boot = {
     loader = {

nix/london/vfio.nix

@@ -0,0 +1,37 @@
+let
+  # RTX 3070 Ti
+  gpuIDs = [
+    "10de:1b81" # Graphics
+    "10de:10f0" # Audio
+  ];
+in { pkgs, lib, config, ... }: {
+  options.vfio.enable = with lib;
+    mkEnableOption "Configure the machine for VFIO";
+
+  config = let cfg = config.vfio;
+  in {
+    boot = {
+      initrd.kernelModules = [
+        "vfio_pci"
+        "vfio"
+        "vfio_iommu_type1"
+
+        "nvidia"
+        "nvidia_modeset"
+        "nvidia_uvm"
+        "nvidia_drm"
+      ];
+
+      kernelParams = [
+        # enable IOMMU
+        "amd_iommu=on"
+        "pcie_acs_override=downstream,multifunction"
+      ] ++ lib.optional cfg.enable
+        # isolate the GPU
+        ("vfio-pci.ids=" + lib.concatStringsSep "," gpuIDs);
+    };
+
+    hardware.opengl.enable = true;
+    virtualisation.spiceUSBRedirection.enable = true;
+  };
+}