qemu: add option microvm.qemu.machine to opt back for q35

Author: astro

CHANGELOG.md

@@ -9,8 +9,9 @@
   Generator** instead of KVM.
 * **SSH deployment scripts** are added as
   `config.microvm.deploy.rebuild`
-* **qemu** gets rid of the *q35* machine model entirely as the
-  *microvm* model supports PCI, USB, and ACPI by now.
+* **qemu** defaults to the *microvm* machine model now as it supports
+  PCI, USB, and ACPI by now. Set `microvm.qemu.machine = "q35"` if
+  this breaks for you.
 * The NixOS **hardened** profile can be used by falling back to
   *squashfs*.
 * Runners execute the hypervisor with a process name of

lib/runners/qemu.nix

@@ -39,7 +39,7 @@ let
     pkgs.qemu_kvm else pkgs.buildPackages.qemu_full);
 
   inherit (microvmConfig) hostName cpu vcpu mem balloonMem user interfaces shares socket forwardPorts devices vsock graphics storeOnDisk kernel initrdPath storeDisk;
-  inherit (microvmConfig.qemu) extraArgs serialConsole;
+  inherit (microvmConfig.qemu) machine extraArgs serialConsole;
 
   inherit (import ../. { nixpkgs-lib = pkgs.lib; }) withDriveLetters;
 
@@ -75,18 +75,22 @@ let
     shares != [] ||
     pciInDevices;
 
-  machine = {
-    x86_64-linux = builtins.concatStringsSep "," [
-      "microvm"
+  machineConfig = builtins.concatStringsSep "," {
+    x86_64-linux = [
+      machine
       accel
       "mem-merge=on"
+      "acpi=on"
+    ] ++ lib.optionals (machine == "microvm") [
       "pit=off"
       "pic=off"
-      "acpi=on"
       "pcie=${if requirePci then "on" else "off"}"
       "usb=${if requireUsb then "on" else "off"}"
     ];
-    aarch64-linux = "virt,gic-version=max,${accel}";
+    aarch64-linux = [
+      "virt"
+      "gic-version=max,${accel}"
+    ];
   }.${system};
 
   devType =
@@ -139,7 +143,7 @@ in {
     [
       "${qemu}/bin/qemu-system-${arch}"
       "-name" hostName
-      "-M" machine
+      "-M" machineConfig
       "-m" (toString (mem + balloonMem))
       "-smp" (toString vcpu)
       "-nodefaults" "-no-user-config"

nixos-modules/microvm/options.nix

@@ -1,4 +1,4 @@
-{ config, options, lib, ... }:
+{ config, options, lib, pkgs, ... }:
 let
   self-lib = import ../../lib {
     nixpkgs-lib = lib;
@@ -393,6 +393,19 @@ in
       '';
     };
 
+    qemu.machine = mkOption {
+      type = types.str;
+      default = {
+        x86_64-linux = "microvm";
+        aarch64-linux = "virt";
+      }.${pkgs.system};
+      description = ''
+        QEMU machine model, eg. `microvm`, or `q35`
+
+        Get a full list with `qemu-system-x86_64 -M help`
+      '';
+    };
+
     qemu.extraArgs = mkOption {
       type = with types; listOf str;
       default = [];