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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>
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@ -72,6 +72,9 @@ struct e820map {
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#define BIOS_BEGIN 0x000a0000
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#define BIOS_BEGIN 0x000a0000
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#define BIOS_END 0x00100000
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#define BIOS_END 0x00100000
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#define BIOS_ROM_BASE 0xffe00000
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#define BIOS_ROM_END 0xffffffff
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#ifdef __KERNEL__
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#ifdef __KERNEL__
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/* see comment in arch/x86/kernel/e820.c */
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/* see comment in arch/x86/kernel/e820.c */
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extern struct e820map e820;
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extern struct e820map e820;
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@ -37,10 +37,11 @@ static void remove_e820_regions(struct resource *avail)
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void arch_remove_reservations(struct resource *avail)
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void arch_remove_reservations(struct resource *avail)
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{
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{
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/* Trim out BIOS area (low 1MB) and E820 regions */
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/* Trim out BIOS areas (low 1MB and high 2MB) and E820 regions */
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if (avail->flags & IORESOURCE_MEM) {
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if (avail->flags & IORESOURCE_MEM) {
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if (avail->start < BIOS_END)
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if (avail->start < BIOS_END)
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avail->start = BIOS_END;
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avail->start = BIOS_END;
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resource_clip(avail, BIOS_ROM_BASE, BIOS_ROM_END);
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remove_e820_regions(avail);
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remove_e820_regions(avail);
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}
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}
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