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Date: Thu, 12 Feb 2009 13:37:21 +0100 (CET)
From: Andi Kleen <andi@...stfloor.org>
To: akpm@...ux-foundation.org, x86@...stfloor.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] [2/10] x86: MCE: Don't disable machine checks during code patching
Impact: low priority bug fix
This removes part of a a patch I added myself some time ago. After some
consideration the patch was a bad idea. In particular it stopped machine check
exceptions during code patching.
To quote the comment:
* MCEs only happen when something got corrupted and in this
* case we must do something about the corruption.
* Ignoring it is worse than a unlikely patching race.
* Also machine checks tend to be broadcast and if one CPU
* goes into machine check the others follow quickly, so we don't
* expect a machine check to cause undue problems during to code
* patching.
So undo the machine check related parts of
8f4e956b313dcccbc7be6f10808952345e3b638c NMIs are still disabled.
This only removes code, the only additions are a new comment.
Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
arch/x86/include/asm/mce.h | 2 --
arch/x86/kernel/alternative.c | 17 +++++++++++------
arch/x86/kernel/cpu/mcheck/mce_32.c | 14 --------------
arch/x86/kernel/cpu/mcheck/mce_64.c | 14 --------------
4 files changed, 11 insertions(+), 36 deletions(-)
Index: linux/arch/x86/kernel/alternative.c
===================================================================
--- linux.orig/arch/x86/kernel/alternative.c 2009-02-12 11:30:51.000000000 +0100
+++ linux/arch/x86/kernel/alternative.c 2009-02-12 11:30:51.000000000 +0100
@@ -414,9 +414,17 @@
that might execute the to be patched code.
Other CPUs are not running. */
stop_nmi();
-#ifdef CONFIG_X86_MCE
- stop_mce();
-#endif
+
+ /*
+ * Don't stop machine check exceptions while patching.
+ * MCEs only happen when something got corrupted and in this
+ * case we must do something about the corruption.
+ * Ignoring it is worse than a unlikely patching race.
+ * Also machine checks tend to be broadcast and if one CPU
+ * goes into machine check the others follow quickly, so we don't
+ * expect a machine check to cause undue problems during to code
+ * patching.
+ */
apply_alternatives(__alt_instructions, __alt_instructions_end);
@@ -456,9 +464,6 @@
(unsigned long)__smp_locks_end);
restart_nmi();
-#ifdef CONFIG_X86_MCE
- restart_mce();
-#endif
}
/**
Index: linux/arch/x86/kernel/cpu/mcheck/mce_64.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 11:30:51.000000000 +0100
+++ linux/arch/x86/kernel/cpu/mcheck/mce_64.c 2009-02-12 12:10:22.000000000 +0100
@@ -680,20 +680,6 @@
&mce_chrdev_ops,
};
-static unsigned long old_cr4 __initdata;
-
-void __init stop_mce(void)
-{
- old_cr4 = read_cr4();
- clear_in_cr4(X86_CR4_MCE);
-}
-
-void __init restart_mce(void)
-{
- if (old_cr4 & X86_CR4_MCE)
- set_in_cr4(X86_CR4_MCE);
-}
-
/*
* Old style boot options parsing. Only for compatibility.
*/
Index: linux/arch/x86/include/asm/mce.h
===================================================================
--- linux.orig/arch/x86/include/asm/mce.h 2009-02-12 11:30:51.000000000 +0100
+++ linux/arch/x86/include/asm/mce.h 2009-02-12 12:10:19.000000000 +0100
@@ -120,8 +120,6 @@
#else
#define mcheck_init(c) do { } while (0)
#endif
-extern void stop_mce(void);
-extern void restart_mce(void);
#endif /* __KERNEL__ */
#endif /* _ASM_X86_MCE_H */
Index: linux/arch/x86/kernel/cpu/mcheck/mce_32.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/mcheck/mce_32.c 2009-02-12 11:30:51.000000000 +0100
+++ linux/arch/x86/kernel/cpu/mcheck/mce_32.c 2009-02-12 11:30:51.000000000 +0100
@@ -60,20 +60,6 @@
}
}
-static unsigned long old_cr4 __initdata;
-
-void __init stop_mce(void)
-{
- old_cr4 = read_cr4();
- clear_in_cr4(X86_CR4_MCE);
-}
-
-void __init restart_mce(void)
-{
- if (old_cr4 & X86_CR4_MCE)
- set_in_cr4(X86_CR4_MCE);
-}
-
static int __init mcheck_disable(char *str)
{
mce_disabled = 1;
--
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