diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 08c5d04..e052780 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -44,10 +44,20 @@
              maxcpus=2 will only boot 2. You can choose to bring the
              other cpus later online, read FAQ's for more info.
 
-additional_cpus=n	[x86_64 only] use this to limit hotpluggable cpus.
-                        This option sets
+additional_cpus*=n	Use this to limit hotpluggable cpus. This option sets
 			cpu_possible_map = cpu_present_map + additional_cpus
 
+(*) Option valid only for following architectures
+- x86_64, ia64
+
+ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
+to determine the number of potentially hot-pluggable cpus. The implementation
+should only rely on this to count the #of cpus, but *MUST* not rely on the
+apicid values in those tables for disabled apics. In the event BIOS doesnt
+mark such hot-pluggable cpus as disabled entries, one could use this
+parameter "additional_cpus=x" to represent those cpus in the cpu_possible_map.
+
+
 CPU maps and such
 -----------------
 [More on cpumaps and primitive to manipulate, please check