amazon-image.nix: add EFI support, enable by default for aarch64

nixos/maintainers/scripts/ec2/amazon-image.nix

@@ -51,7 +51,9 @@ in {
     inherit lib config;
     inherit (cfg) contents format name;
     pkgs = import ../../../.. { inherit (pkgs) system; }; # ensure we use the regular qemu-kvm package
-    partitionTableType = if config.ec2.hvm then "legacy" else "none";
+    partitionTableType = if config.ec2.efi then "efi"
+                         else if config.ec2.hvm then "legacy"
+                         else "none";
     diskSize = cfg.sizeMB;
     fsType = "ext4";
     configFile = pkgs.writeText "configuration.nix"
@@ -61,6 +63,9 @@ in {
           ${optionalString config.ec2.hvm ''
             ec2.hvm = true;
           ''}
+          ${optionalString config.ec2.efi ''
+            ec2.efi = true;
+          ''}
         }
       '';
   };

nixos/modules/virtualisation/amazon-image.nix

@@ -25,6 +25,9 @@ in
       { assertion = cfg.hvm;
         message = "Paravirtualized EC2 instances are no longer supported.";
       }
+      { assertion = cfg.efi -> cfg.hvm;
+        message = "EC2 instances using EFI must be HVM instances.";
+      }
     ];
 
     boot.growPartition = cfg.hvm;
@@ -35,6 +38,11 @@ in
       autoResize = true;
     };
 
+    fileSystems."/boot" = mkIf cfg.efi {
+      device = "/dev/disk/by-label/ESP";
+      fsType = "vfat";
+    };
+
     boot.extraModulePackages = [
       config.boot.kernelPackages.ena
     ];
@@ -50,8 +58,10 @@ in
 
     # Generate a GRUB menu.  Amazon's pv-grub uses this to boot our kernel/initrd.
     boot.loader.grub.version = if cfg.hvm then 2 else 1;
-    boot.loader.grub.device = if cfg.hvm then "/dev/xvda" else "nodev";
+    boot.loader.grub.device = if (cfg.hvm && !cfg.efi) then "/dev/xvda" else "nodev";
     boot.loader.grub.extraPerEntryConfig = mkIf (!cfg.hvm) "root (hd0)";
+    boot.loader.grub.efiSupport = cfg.efi;
+    boot.loader.grub.efiInstallAsRemovable = cfg.efi;
     boot.loader.timeout = 0;
 
     boot.initrd.network.enable = true;

nixos/modules/virtualisation/amazon-options.nix

@@ -1,4 +1,4 @@
-{ config, lib, ... }:
+{ config, lib, pkgs, ... }:
 {
   options = {
     ec2 = {
@@ -9,6 +9,13 @@
           Whether the EC2 instance is a HVM instance.
         '';
       };
+      efi = lib.mkOption {
+        default = pkgs.stdenv.hostPlatform.isAarch64;
+        internal = true;
+        description = ''
+          Whether the EC2 instance is using EFI.
+        '';
+      };
     };
   };
 }