From: Vivek Goyal <vgoyal@in.ibm.com>

This patch retrieves the max_pfn being used by previous kernel and stores it
in a safe location (saved_max_pfn) before it is overwritten due to user
defined memory map.  This pfn is used to make sure that user does not try to
read the physical memory beyond saved_max_pfn.

Signed-off-by: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 arch/i386/kernel/setup.c |   12 ++++++++++++
 include/linux/bootmem.h  |    4 ++++
 mm/bootmem.c             |    8 ++++++++
 3 files changed, 24 insertions(+)

diff -puN arch/i386/kernel/setup.c~kdump-retrieve-saved-max-pfn arch/i386/kernel/setup.c
--- 25/arch/i386/kernel/setup.c~kdump-retrieve-saved-max-pfn	2005-05-09 20:10:01.000000000 -0700
+++ 25-akpm/arch/i386/kernel/setup.c	2005-05-09 20:10:01.000000000 -0700
@@ -58,6 +58,9 @@
 #include "setup_arch_pre.h"
 #include <bios_ebda.h>
 
+/* Forward Declaration. */
+void __init find_max_pfn(void);
+
 /* This value is set up by the early boot code to point to the value
    immediately after the boot time page tables.  It contains a *physical*
    address, and must not be in the .bss segment! */
@@ -716,6 +719,15 @@ static void __init parse_cmdline_early (
 			if (to != command_line)
 				to--;
 			if (!memcmp(from+7, "exactmap", 8)) {
+#ifdef CONFIG_CRASH_DUMP
+				/* If we are doing a crash dump, we
+				 * still need to know the real mem
+				 * size before original memory map is
+				 * reset.
+				 */
+				find_max_pfn();
+				saved_max_pfn = max_pfn;
+#endif
 				from += 8+7;
 				e820.nr_map = 0;
 				userdef = 1;
diff -puN include/linux/bootmem.h~kdump-retrieve-saved-max-pfn include/linux/bootmem.h
--- 25/include/linux/bootmem.h~kdump-retrieve-saved-max-pfn	2005-05-09 20:10:01.000000000 -0700
+++ 25-akpm/include/linux/bootmem.h	2005-05-09 20:10:01.000000000 -0700
@@ -22,6 +22,10 @@ extern unsigned long min_low_pfn;
  */
 extern unsigned long max_pfn;
 
+#ifdef CONFIG_CRASH_DUMP
+extern unsigned long saved_max_pfn;
+#endif
+
 /*
  * node_bootmem_map is a map pointer - the bits represent all physical 
  * memory pages (including holes) on the node.
diff -puN mm/bootmem.c~kdump-retrieve-saved-max-pfn mm/bootmem.c
--- 25/mm/bootmem.c~kdump-retrieve-saved-max-pfn	2005-05-09 20:10:01.000000000 -0700
+++ 25-akpm/mm/bootmem.c	2005-05-09 20:10:01.000000000 -0700
@@ -33,6 +33,14 @@ EXPORT_SYMBOL(max_pfn);		/* This is expo
 				 * dma_get_required_mask(), which uses
 				 * it, can be an inline function */
 
+#ifdef CONFIG_CRASH_DUMP
+/*
+ * If we have booted due to a crash, max_pfn will be a very low value. We need
+ * to know the amount of memory that the previous kernel used.
+ */
+unsigned long saved_max_pfn;
+#endif
+
 /* return the number of _pages_ that will be allocated for the boot bitmap */
 unsigned long __init bootmem_bootmap_pages (unsigned long pages)
 {
_