[PATCH v2] Hibernate: Do not assume the first e820 area to be RAM

["Lee, Chun-Yi" <joeyli.kernel@gmail.com>]

In arch/x86/kernel/setup.c::trim_bios_range(), the codes introduced
by 1b5576e6 (base on d8a9e6a5), it updates the first 4Kb of memory
to be E820_RESERVED region. That's because it's a BIOS owned area
but generally not listed in the E820 table:

[    0.000000] e820: BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x0000000000096fff] usable
[    0.000000] BIOS-e820: [mem 0x0000000000097000-0x0000000000097fff] reserved
...
[    0.000000] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable

But the region of first 4Kb didn't register to nosave memory:

[    0.000000] PM: Registered nosave memory: [mem 0x00097000-0x00097fff]
[    0.000000] PM: Registered nosave memory: [mem 0x000a0000-0x000fffff]

The codes in e820_mark_nosave_regions() assumes the first e820 area to be
RAM, so it causes the first 4Kb E820_RESERVED region ignored when register
to nosave. This patch removed assumption of the first e820 area.

v2:
To avoid the i > 0 checking in for loop. (coding suggestion from Yinghai Lu)

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Len Brown <len.brown@intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
---
 arch/x86/kernel/e820.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Index: linux-3.12-SLE12/arch/x86/kernel/e820.c
===================================================================
--- linux-3.12-SLE12.orig/arch/x86/kernel/e820.c
+++ linux-3.12-SLE12/arch/x86/kernel/e820.c
@@ -682,15 +682,14 @@ void __init parse_e820_ext(u64 phys_addr
  * hibernation (32 bit) or software suspend and suspend to RAM (64 bit).
  *
  * This function requires the e820 map to be sorted and without any
- * overlapping entries and assumes the first e820 area to be RAM.
+ * overlapping entries.
  */
 void __init e820_mark_nosave_regions(unsigned long limit_pfn)
 {
 	int i;
-	unsigned long pfn;
+	unsigned long pfn = 0;
 
-	pfn = PFN_DOWN(e820.map[0].addr + e820.map[0].size);
-	for (i = 1; i < e820.nr_map; i++) {
+	for (i = 0; i < e820.nr_map; i++) {
 		struct e820entry *ei = &e820.map[i];
 
 		if (pfn < PFN_UP(ei->addr))