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>

diff --git a/arch/x86/include/asm/e820.h b/arch/x86/include/asm/e820.h
index 5be1542..e99d55d 100644 (file)
--- 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 89638af..2a26819 100644 (file)
--- 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);
        }