linux/arch/x86/kernel/resource.c
Bjorn Helgaas a2c606d53a 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>
2010-12-17 10:01:30 -08:00

49 lines
1.0 KiB
C

#include <linux/ioport.h>
#include <asm/e820.h>
static void resource_clip(struct resource *res, resource_size_t start,
resource_size_t end)
{
resource_size_t low = 0, high = 0;
if (res->end < start || res->start > end)
return; /* no conflict */
if (res->start < start)
low = start - res->start;
if (res->end > end)
high = res->end - end;
/* Keep the area above or below the conflict, whichever is larger */
if (low > high)
res->end = start - 1;
else
res->start = end + 1;
}
static void remove_e820_regions(struct resource *avail)
{
int i;
struct e820entry *entry;
for (i = 0; i < e820.nr_map; i++) {
entry = &e820.map[i];
resource_clip(avail, entry->addr,
entry->addr + entry->size - 1);
}
}
void arch_remove_reservations(struct resource *avail)
{
/* 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);
}
}