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Commit a2c606d5 authored by Bjorn Helgaas's avatar Bjorn Helgaas Committed by Jesse Barnes
Browse files

x86: avoid high BIOS area when allocating address space 

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: default avatarH. Peter Anvin <hpa@zytor.com>
Signed-off-by: default avatarBjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: default avatarJesse Barnes <jbarnes@virtuousgeek.org>
parent 4dc2287c

arch/x86/include/asm/e820.h

+3 −0
Original line number Diff line number Diff line
@@ -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;

arch/x86/kernel/resource.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

	}