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Revision 4dc2287c1805e7fe8a7cb90bbcd44abee8cdb914 authored by Bjorn Helgaas on 16 December 2010, 17:38:56 UTC, committed by Jesse Barnes on 17 December 2010, 18:01:24 UTC 
x86: avoid E820 regions when allocating address space
 
When we allocate address space, e.g., to assign it to a PCI device, don't
allocate anything mentioned in the BIOS E820 memory map.

On recent machines (2008 and newer), we assign PCI resources from the
windows described by the ACPI PCI host bridge _CRS.  On many Dell
machines, these windows overlap some E820 reserved areas, e.g.,

    BIOS-e820: 00000000bfe4dc00 - 00000000c0000000 (reserved)
    pci_root PNP0A03:00: host bridge window [mem 0xbff00000-0xdfffffff]

If we put devices at 0xbff00000, they don't work, probably because
that's really RAM, not I/O memory.  This patch prevents that by removing
the 0xbfe4dc00-0xbfffffff area from the "available" resource.

I'm not very happy with this solution because Windows solves the problem
differently (it seems to ignore E820 reserved areas and it allocates
top-down instead of bottom-up; details at comment 45 of the bugzilla
below).  That means we're vulnerable to BIOS defects that Windows would not
trip over.  For example, if BIOS described a device in ACPI but didn't
mention it in E820, Windows would work fine but Linux would fail.

Reference: https://bugzilla.kernel.org/show_bug.cgi?id=16228
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>
1 parent 30919b0
Raw File
dsfield.h 
/* include/net/dsfield.h - Manipulation of the Differentiated Services field */

/* Written 1998-2000 by Werner Almesberger, EPFL ICA */


#ifndef __NET_DSFIELD_H
#define __NET_DSFIELD_H

#include <linux/types.h>
#include <linux/ip.h>
#include <linux/ipv6.h>
#include <asm/byteorder.h>


static inline __u8 ipv4_get_dsfield(const struct iphdr *iph)
{
	return iph->tos;
}


static inline __u8 ipv6_get_dsfield(const struct ipv6hdr *ipv6h)
{
	return ntohs(*(const __be16 *)ipv6h) >> 4;
}


static inline void ipv4_change_dsfield(struct iphdr *iph,__u8 mask,
    __u8 value)
{
        __u32 check = ntohs((__force __be16)iph->check);
	__u8 dsfield;

	dsfield = (iph->tos & mask) | value;
	check += iph->tos;
	if ((check+1) >> 16) check = (check+1) & 0xffff;
	check -= dsfield;
	check += check >> 16; /* adjust carry */
	iph->check = (__force __sum16)htons(check);
	iph->tos = dsfield;
}


static inline void ipv6_change_dsfield(struct ipv6hdr *ipv6h,__u8 mask,
    __u8 value)
{
        __u16 tmp;

	tmp = ntohs(*(__be16 *) ipv6h);
	tmp = (tmp & ((mask << 4) | 0xf00f)) | (value << 4);
	*(__be16 *) ipv6h = htons(tmp);
}


#endif
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