x86_32: trim memory by updating e820

when MTRRs are not covering the whole e820 table, we need to trim the
RAM and need to update e820.

reuse some code on 64-bit as well.

here need to add early_get_cap and use it in early_cpu_detect, and move
mtrr_bp_init early.

The code successfully trimmed the memory map on Justin's system:

from:

 [    0.000000]  BIOS-e820: 0000000100000000 - 000000022c000000 (usable)

to:

 [    0.000000]   modified: 0000000100000000 - 0000000228000000 (usable)
 [    0.000000]   modified: 0000000228000000 - 000000022c000000 (reserved)

According to Justin it makes quite a difference:

|  When I boot the box without any trimming it acts like a 286 or 386,
|  takes about 10 minutes to boot (using raptor disks).

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Tested-by: Justin Piszcz <jpiszcz@lucidpixels.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/x86/kernel/e820_32.c b/arch/x86/kernel/e820_32.c
index 931934a7b35..4e16ef4a265 100644
--- a/arch/x86/kernel/e820_32.c
+++ b/arch/x86/kernel/e820_32.c
@@ -749,3 +749,14 @@ static int __init parse_memmap(char *arg)
 	return 0;
 }
 early_param("memmap", parse_memmap);
+void __init update_e820(void)
+{
+	u8 nr_map;
+
+	nr_map = e820.nr_map;
+	if (sanitize_e820_map(e820.map, &nr_map))
+		return;
+	e820.nr_map = nr_map;
+	printk(KERN_INFO "modified physical RAM map:\n");
+	print_memory_map("modified");
+}