1 files changed, 56 insertions, 38 deletions

diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 91abf5b2fb94..41c480ae47df 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -139,9 +139,64 @@ void __init e820_print_map(char *who)
  * Sanitize the BIOS e820 map.
  *
  * Some e820 responses include overlapping entries. The following
- * replaces the original e820 map with a new one, removing overlaps.
+ * replaces the original e820 map with a new one, removing overlaps,
+ * and resolving conflicting memory types in favor of highest
+ * numbered type.
  *
+ * The input parameter biosmap points to an array of 'struct
+ * e820entry' which on entry has elements in the range [0, *pnr_map)
+ * valid, and which has space for up to max_nr_map entries.
+ * On return, the resulting sanitized e820 map entries will be in
+ * overwritten in the same location, starting at biosmap.
+ *
+ * The integer pointed to by pnr_map must be valid on entry (the
+ * current number of valid entries located at biosmap) and will
+ * be updated on return, with the new number of valid entries
+ * (something no more than max_nr_map.)
+ *
+ * The return value from sanitize_e820_map() is zero if it
+ * successfully 'sanitized' the map entries passed in, and is -1
+ * if it did nothing, which can happen if either of (1) it was
+ * only passed one map entry, or (2) any of the input map entries
+ * were invalid (start + size < start, meaning that the size was
+ * so big the described memory range wrapped around through zero.)
+ *
+ *      Visually we're performing the following
+ *      (1,2,3,4 = memory types)...
+ *
+ *      Sample memory map (w/overlaps):
+ *         ____22__________________
+ *         ______________________4_
+ *         ____1111________________
+ *         _44_____________________
+ *         11111111________________
+ *         ____________________33__
+ *         ___________44___________
+ *         __________33333_________
+ *         ______________22________
+ *         ___________________2222_
+ *         _________111111111______
+ *         _____________________11_
+ *         _________________4______
+ *
+ *      Sanitized equivalent (no overlap):
+ *         1_______________________
+ *         _44_____________________
+ *         ___1____________________
+ *         ____22__________________
+ *         ______11________________
+ *         _________1______________
+ *         __________3_____________
+ *         ___________44___________
+ *         _____________33_________
+ *         _______________2________
+ *         ________________1_______
+ *         _________________4______
+ *         ___________________2____
+ *         ____________________33__
+ *         ______________________4_
  */
+
 int __init sanitize_e820_map(struct e820entry *biosmap, int max_nr_map,
                                 int *pnr_map)
 {
@@ -162,43 +217,6 @@ static struct e820entry new_bios[E820_X_MAX] __initdata;
         int old_nr, new_nr, chg_nr;
         int i;
 
-        /*
-                Visually we're performing the following
-                (1,2,3,4 = memory types)...
-
-                Sample memory map (w/overlaps):
-                   ____22__________________
-                   ______________________4_
-                   ____1111________________
-                   _44_____________________
-                   11111111________________
-                   ____________________33__
-                   ___________44___________
-                   __________33333_________
-                   ______________22________
-                   ___________________2222_
-                   _________111111111______
-                   _____________________11_
-                   _________________4______
-
-                Sanitized equivalent (no overlap):
-                   1_______________________
-                   _44_____________________
-                   ___1____________________
-                   ____22__________________
-                   ______11________________
-                   _________1______________
-                   __________3_____________
-                   ___________44___________
-                   _____________33_________
-                   _______________2________
-                   ________________1_______
-                   _________________4______
-                   ___________________2____
-                   ____________________33__
-                   ______________________4_
-        */
-
         /* if there's only one memory region, don't bother */
         if (*pnr_map < 2)
                 return -1;