linux-kernel - [GIT PULL] x86 setup BIOS workarounds

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Date:	Wed, 1 Apr 2009 09:40:13 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Michael K. Johnson" <johnsonm@...th.com>,
	Justin Forbes <jmforbes@...uxtx.org>,
	Jordan Hargrave <Jordan_Hargrave@...l.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [GIT PULL] x86 setup BIOS workarounds

Hi Linus,

These three patches work around one identified and two hypothetical
BIOS problems with the E820 memory probe.

The identified problem is one specific box which clobbers %esi; the
other two patches protect %edi and %ebp, and implements handling for
the backwards-incompatible(!) E820 handling in ACPI 3.


The following changes since commit 15f7176eb1cccec0a332541285ee752b935c1c85:
  Linus Torvalds (1):
        Merge git://git.kernel.org/.../davem/net-2.6

are available in the git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git x86/setup

H. Peter Anvin (2):
      x86, setup: preemptively save/restore edi and ebp around INT 15 E820
      x86, setup: ACPI 3, BIOS workaround for E820-probing code

Michael K. Johnson (1):
      x86, setup: mark %esi as clobbered in E820 BIOS call

 arch/x86/boot/memory.c |   33 ++++++++++++++++++++++++---------
 1 files changed, 24 insertions(+), 9 deletions(-)

diff --git a/arch/x86/boot/memory.c b/arch/x86/boot/memory.c
index 8c3c25f..d5d2360 100644
--- 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.
@@ -16,24 +17,32 @@
 
 #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;
 	u32 next = 0;
-	u32 size, id;
+	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 is clobbered by some BIOSes,
-		   so it must be either used for the error output
-		   or explicitly marked clobbered. */
-		asm("int $0x15; setc %0"
+		/* Important: %edx and %esi are clobbered by some BIOSes,
+		   so they must be either used for the error output
+		   or explicitly marked clobbered.  Given that, assume there
+		   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),
-		      "=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
 		   to %ebx = 0 don't always report the SMAP signature on
@@ -51,8 +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;
--
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