829157be59
The proper way to terminate the e820 chain is with %ebx == 0 on the last legitimate memory block. However, several BIOSes don't do that and instead return error (CF = 1) when trying to read off the end of the list. For this error return, %eax doesn't necessarily return the SMAP signature -- correctly so, since %ah should contain an error code in this case. To deal with some particularly broken BIOSes, we clear the entire e820 chain if the SMAP signature is missing in the middle, indicating a plain insane e820 implementation. However, we need to make the test for CF = 1 before the SMAP check. This fixes at least one HP laptop (nc6400) for which none of the memory-probing methods (e820, e801, 88) functioned fully according to spec. Signed-off-by: H. Peter Anvin <hpa@zytor.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
122 lines
2.5 KiB
C
122 lines
2.5 KiB
C
/* -*- linux-c -*- ------------------------------------------------------- *
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*
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* Copyright (C) 1991, 1992 Linus Torvalds
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* Copyright 2007 rPath, Inc. - All Rights Reserved
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*
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* This file is part of the Linux kernel, and is made available under
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* the terms of the GNU General Public License version 2.
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*
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* ----------------------------------------------------------------------- */
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/*
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* arch/i386/boot/memory.c
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*
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* Memory detection code
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*/
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#include "boot.h"
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#define SMAP 0x534d4150 /* ASCII "SMAP" */
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static int detect_memory_e820(void)
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{
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int count = 0;
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u32 next = 0;
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u32 size, id;
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u8 err;
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struct e820entry *desc = boot_params.e820_map;
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do {
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size = sizeof(struct e820entry);
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/* Important: %edx is clobbered by some BIOSes,
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so it must be either used for the error output
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or explicitly marked clobbered. */
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asm("int $0x15; setc %0"
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: "=d" (err), "+b" (next), "=a" (id), "+c" (size),
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"=m" (*desc)
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: "D" (desc), "d" (SMAP), "a" (0xe820));
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/* BIOSes which terminate the chain with CF = 1 as opposed
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to %ebx = 0 don't always report the SMAP signature on
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the final, failing, probe. */
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if (err)
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break;
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/* Some BIOSes stop returning SMAP in the middle of
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the search loop. We don't know exactly how the BIOS
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screwed up the map at that point, we might have a
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partial map, the full map, or complete garbage, so
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just return failure. */
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if (id != SMAP) {
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count = 0;
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break;
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}
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count++;
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desc++;
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} while (next && count < E820MAX);
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return boot_params.e820_entries = count;
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}
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static int detect_memory_e801(void)
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{
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u16 ax, bx, cx, dx;
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u8 err;
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bx = cx = dx = 0;
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ax = 0xe801;
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asm("stc; int $0x15; setc %0"
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: "=m" (err), "+a" (ax), "+b" (bx), "+c" (cx), "+d" (dx));
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if (err)
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return -1;
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/* Do we really need to do this? */
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if (cx || dx) {
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ax = cx;
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bx = dx;
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}
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if (ax > 15*1024)
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return -1; /* Bogus! */
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/* This ignores memory above 16MB if we have a memory hole
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there. If someone actually finds a machine with a memory
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hole at 16MB and no support for 0E820h they should probably
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generate a fake e820 map. */
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boot_params.alt_mem_k = (ax == 15*1024) ? (dx << 6)+ax : ax;
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return 0;
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}
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static int detect_memory_88(void)
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{
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u16 ax;
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u8 err;
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ax = 0x8800;
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asm("stc; int $0x15; setc %0" : "=bcdm" (err), "+a" (ax));
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boot_params.screen_info.ext_mem_k = ax;
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return -err;
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}
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int detect_memory(void)
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{
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int err = -1;
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if (detect_memory_e820() > 0)
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err = 0;
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if (!detect_memory_e801())
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err = 0;
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if (!detect_memory_88())
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err = 0;
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return err;
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}
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