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: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index fcdb10add9c8219f39df24b38bfee2e2e46d2792..d5d2360763dc0e7e4512e9a63987d0aff89097d2 100644 (file)
--- a/arch/x86/boot/memory.c
+++ b/arch/x86/boot/memory.c
@@ -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;