From a2c606d53ab71dee6410f10ef0adf67321d60e06 Mon Sep 17 00:00:00 2001
From: Bjorn Helgaas <bjorn.helgaas@hp.com>
Date: Thu, 16 Dec 2010 10:39:02 -0700
Subject: [PATCH] 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: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
---
arch/x86/include/asm/e820.h | 3 +++
arch/x86/kernel/resource.c | 3 ++-
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h
index 5be1542fbfaf..e99d55d74df5 100644
--- a/arch/x86/include/asm/e820.h
+++ b/arch/x86/include/asm/e820.h
@@ -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;
diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
index 89638af2ff19..2a26819bb6a8 100644
--- a/arch/x86/kernel/resource.c
+++ b/arch/x86/kernel/resource.c
@@ -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);
}
--
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