diff -r 774dfc178c39 xen/arch/x86/acpi/cpuidle_menu.c
--- a/xen/arch/x86/acpi/cpuidle_menu.c	Thu Aug 12 17:06:21 2010 +0100
+++ b/xen/arch/x86/acpi/cpuidle_menu.c	Mon Aug 16 17:33:05 2010 -0500
@@ -272,6 +272,11 @@
 {
     struct menu_device *data = &per_cpu(menu_devices, power->cpu);
 
+    if (!cpu_online(power->cpu))
+    {
+        return -1;
+    }
+
     memset(data, 0, sizeof(struct menu_device));
 
     return 0;