diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 6887d44d266188c9d5d17fc267b2441cc82d8e39..6da24e7a56cba01c9b7af0a0e1c894667a614d75 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -238,6 +238,13 @@ Debugging
   pagefaulttrace Dump all page faults. Only useful for extreme debugging
 		and will create a lot of output.
 
+  call_trace=[old|both|newfallback|new]
+		old: use old inexact backtracer
+		new: use new exact dwarf2 unwinder
+ 		both: print entries from both
+		newfallback: use new unwinder but fall back to old if it gets
+			stuck (default)
+
 Misc
 
   noreplacement  Don't replace instructions with more appropriate ones