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x86: avoid high BIOS area when allocating address space

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This prevents allocation of the last 2MB before 4GB.

The experiment described here shows Windows 7 ignoring the last 1MB:
https://bugzilla.kernel.org/show_bug.cgi?id=23542#c27

This patch ignores the top 2MB instead of just 1MB because H. Peter Anvin
says "There will be ROM at the top of the 32-bit address space; it's a fact
of the architecture, and on at least older systems it was common to have a
shadow 1 MiB below."

Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
This commit is contained in:
Bjorn Helgaas 2010-12-16 10:39:02 -07:00 committed by Jesse Barnes
parent 4dc2287c18
commit a2c606d53a
2 changed files with 5 additions and 1 deletions
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3
arch/x86/include/asm/e820.h
View File

@ -72,6 +72,9 @@ struct e820map {
#define BIOS_BEGIN 0x000a0000
#define BIOS_END 0x00100000
#define BIOS_ROM_BASE 0xffe00000
#define BIOS_ROM_END 0xffffffff
#ifdef __KERNEL__
/* see comment in arch/x86/kernel/e820.c */
extern struct e820map e820;

3
arch/x86/kernel/resource.c
View File

@ -37,10 +37,11 @@ static void remove_e820_regions(struct resource *avail)
void arch_remove_reservations(struct resource *avail)
{
/* Trim out BIOS area (low 1MB) and E820 regions */
/* Trim out BIOS areas (low 1MB and high 2MB) and E820 regions */
if (avail->flags & IORESOURCE_MEM) {
if (avail->start < BIOS_END)
avail->start = BIOS_END;
resource_clip(avail, BIOS_ROM_BASE, BIOS_ROM_END);
remove_e820_regions(avail);
}