diff --git a/modules/installer/grub/grub-menu-builder.sh b/modules/installer/grub/grub-menu-builder.sh
index 4caafe9da63b..8934c9bd24de 100644
--- a/modules/installer/grub/grub-menu-builder.sh
+++ b/modules/installer/grub/grub-menu-builder.sh
@@ -190,16 +190,16 @@ EOF
 	name="$confName $3"
     fi
 
-    local kernelArgs="systemConfig=$(readlink -f $path) init=$(readlink -f $path/init) $(cat $path/kernel-params)"
-    local xenArgs="loglvl=all guest_loglvl=all"
+    local kernelParams="systemConfig=$(readlink -f $path) init=$(readlink -f $path/init) $(cat $path/kernel-params)"
+    local xenParams="$([ -n "$xen" ] && cat $path/xen-params)"
 
     case "$grubVersion" in
 	1)
 	    cat >> "$tmp" << GRUBEND
 title $name
   @extraPerEntryConfig@
-  ${xen:+kernel $xen $xenArgs}
-  $(if [ -z "$xen" ]; then echo kernel; else echo module; fi) $kernel $kernelArgs
+  ${xen:+kernel $xen $xenParams}
+  $(if [ -z "$xen" ]; then echo kernel; else echo module; fi) $kernel $kernelParams
   module $initrd
 GRUBEND
 	    ;;
@@ -207,8 +207,8 @@ GRUBEND
 	    cat >> "$tmp" << GRUBEND
 menuentry "$name" {
   @extraPerEntryConfig@
-  ${xen:+multiboot $xen $xenArgs}
-  $(if [ -z "$xen" ]; then echo linux; else echo module; fi) $kernel $kernelArgs
+  ${xen:+multiboot $xen $xenParams}
+  $(if [ -z "$xen" ]; then echo linux; else echo module; fi) $kernel $kernelParams
   $(if [ -z "$xen" ]; then echo initrd; else echo module; fi) $initrd
 }
 GRUBEND
diff --git a/modules/module-list.nix b/modules/module-list.nix
index 5a1efdabf411..973c3a3e4939 100644
--- a/modules/module-list.nix
+++ b/modules/module-list.nix
@@ -154,4 +154,5 @@
   ./tasks/network-interfaces.nix
   ./tasks/swraid.nix
   ./tasks/tty-backgrounds.nix
+  ./virtualisation/xen.nix
 ]
diff --git a/modules/system/activation/top-level.nix b/modules/system/activation/top-level.nix
index cb3c4e8941dc..f2bbbc5ffb0d 100644
--- a/modules/system/activation/top-level.nix
+++ b/modules/system/activation/top-level.nix
@@ -43,30 +43,19 @@ let
     system.copySystemConfiguration = pkgs.lib.mkOption {
       default = false;
       description = ''
-        Unless set to false copies the nixos configuration file
-        <literal>$NIXOS_CONFIG</literal> defaulting to
-        <filename>/etc/nixos/configuration.nix</filename>
+        If enabled, copies the NixOS configuration file
+        <literal>$NIXOS_CONFIG</literal> (usually
+        <filename>/etc/nixos/configuration.nix</filename>)
         to the system store path.
-        See <option>extraSystemBuilderCmds</option>
-        if you want to do add more customized info
-        to your system storepath.
       '';
     };
 
     system.extraSystemBuilderCmds = pkgs.lib.mkOption {
       default = "";
+      internal = true;
       merge = pkgs.lib.concatStringsSep "\n";
       description = ''
         This code will be added to the builder creating the system store path.
-        This use case copies your configuration file into the system derivation:
-        <command>
-        cp ${pkgs.lib.maybeEnv "NIXOS_CONFIG" "/etc/nixos/configuration.nix"} $out
-        </command>
-        Of course you could add code saving a svn diff or svn revision number
-        of both nixos and nixpkgs repositories as well. Keep in mind that when
-        you build in chroots that you have do either copy sources to store or
-        add them to the chroot somehow.
-        You still should consider putting your configuration into a VCS.
       '';
     };
     
@@ -107,6 +96,7 @@ let
         echo "(Expecting ${kernelPath})"
         false
       fi
+
       ln -s ${kernelPath} $out/kernel
       ln -s ${config.system.modulesTree} $out/kernel-modules
       if [ -n "$grub" ]; then 
@@ -181,8 +171,9 @@ in {
   require = [options];
 
   system.extraSystemBuilderCmds =
-      pkgs.lib.optionalString
-          config.system.copySystemConfiguration
-          "cp ${pkgs.lib.maybeEnv "NIXOS_CONFIG" "/etc/nixos/configuration.nix"} $out";
+    pkgs.lib.optionalString
+      config.system.copySystemConfiguration
+      "cp ${pkgs.lib.maybeEnv "NIXOS_CONFIG" "/etc/nixos/configuration.nix"} $out";
+
   system.build.toplevel = system;
 }
diff --git a/modules/virtualisation/xen.nix b/modules/virtualisation/xen.nix
new file mode 100644
index 000000000000..5e8bb902b2a7
--- /dev/null
+++ b/modules/virtualisation/xen.nix
@@ -0,0 +1,76 @@
+# Xen hypervisor support.
+
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let cfg = config.virtualisation.xen; in
+
+{
+  ###### interface
+
+  options = {
+
+    virtualisation.xen.enable = 
+      mkOption {
+        default = false;
+        description =
+          ''
+            Setting this option enables the Xen hypervisor, a
+            virtualisation technology that allows multiple virtual
+            machines, known as <emphasis>domains</emphasis>, to run
+            concurrently on the physical machine.  NixOS runs as the
+            privileged <emphasis>Domain 0</emphasis>.  This option
+            requires a reboot to take effect.
+          '';
+      };
+
+    virtualisation.xen.bootParams = 
+      mkOption {
+        default = "";
+        description =
+          ''
+            Parameters passed to the Xen hypervisor at boot time.
+          '';
+      };
+
+    virtualisation.xen.domain0MemorySize = 
+      mkOption {
+        default = 0;
+        example = 512;
+        description =
+          ''
+            Amount of memory (in MiB) allocated to Domain 0 on boot.
+            If set to 0, all memory is assigned to Domain 0.
+          '';
+      };
+
+  };
+
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    environment.systemPackages = [ pkgs.xen ];
+
+    # Domain 0 requires a pvops-enabled kernel.
+    boot.kernelPackages = pkgs.linuxPackages_2_6_32_xen;
+
+    # The radeonfb kernel module causes the screen to go black as soon
+    # as it's loaded, so don't load it.
+    boot.blacklistedKernelModules = [ "radeonfb" ];
+
+    virtualisation.xen.bootParams = 
+      [ "loglvl=all" "guest_loglvl=all" ] ++
+      optional (cfg.domain0MemorySize != 0) "dom0_mem=${toString cfg.domain0MemorySize}M";
+
+    system.extraSystemBuilderCmds =
+      ''
+        ln -s ${pkgs.xen}/boot/xen.gz $out/xen.gz
+        echo "${toString cfg.bootParams}" > $out/xen-params
+      '';
+
+  };
+
+}