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Commit c549e71d authored by H. Peter Anvin's avatar H. Peter Anvin
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x86, setup: ACPI 3, BIOS workaround for E820-probing code 



Impact: ACPI 3 spec compliance, BIOS bug workaround

The ACPI 3 spec added another field to the E820 buffer -- which is
backwards incompatible, since it contains a validity bit.
Furthermore, there has been at least one report of a BIOS which
assumes that the buffer it is pointed at is the same buffer as for the
previous E820 call.  Therefore, read the data into a temporary buffer
and copy the standard part of it if and only if the valid bit is set.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 32ec7fd0

arch/x86/boot/memory.c

+17 −4
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
 *

 *   Copyright (C) 1991, 1992 Linus Torvalds

 *   Copyright 2007 rPath, Inc. - All Rights Reserved

 *   Copyright 2009 Intel Corporation; author H. Peter Anvin

 *

 *   This file is part of the Linux kernel, and is made available under

 *   the terms of the GNU General Public License version 2.
@@ -16,6 +17,11 @@ 


#define SMAP	0x534d4150	/* ASCII "SMAP" */



struct e820_ext_entry {

	struct e820entry std;

	u32 ext_flags;

} __attribute__((packed));



static int detect_memory_e820(void)

{

	int count = 0;
@@ -23,9 +29,10 @@ static int detect_memory_e820(void) 
	u32 size, id, edi;

	u8 err;

	struct e820entry *desc = boot_params.e820_map;

	static struct e820_ext_entry buf; /* static so it is zeroed */



	do {

		size = sizeof(struct e820entry);

		size = sizeof buf;



		/* Important: %edx and %esi are clobbered by some BIOSes,

		   so they must be either used for the error output
@@ -33,8 +40,8 @@ static int detect_memory_e820(void) 
		   is something out there clobbering %ebp and %edi, too. */

		asm("pushl %%ebp; int $0x15; popl %%ebp; setc %0"

		    : "=d" (err), "+b" (next), "=a" (id), "+c" (size),

		      "=D" (edi), "=m" (*desc)

		    : "D" (desc), "d" (SMAP), "a" (0xe820)

		      "=D" (edi), "+m" (buf)

		    : "D" (&buf), "d" (SMAP), "a" (0xe820)

		    : "esi");



		/* BIOSes which terminate the chain with CF = 1 as opposed
@@ -53,8 +60,14 @@ static int detect_memory_e820(void) 
			break;

		}



		/* ACPI 3.0 added the extended flags support.  If bit 0

		   in the extended flags is zero, we're supposed to simply

		   ignore the entry -- a backwards incompatible change! */

		if (size > 20 && !(buf.ext_flags & 1))

			continue;



		*desc++ = buf.std;

		count++;

		desc++;

	} while (next && count < ARRAY_SIZE(boot_params.e820_map));



	return boot_params.e820_entries = count;