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Subject[PATCH] [4/4] MCE: Don't disable machine checks during code patching
Date

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@linux.intel.com>

---
arch/x86/kernel/alternative.c | 17 +++++++++++------
arch/x86/kernel/cpu/mcheck/mce_32.c | 14 --------------
arch/x86/kernel/cpu/mcheck/mce_64.c | 14 --------------
include/asm-x86/mce.h | 2 --
4 files changed, 11 insertions(+), 36 deletions(-)

Index: linux/arch/x86/kernel/alternative.c
===================================================================
--- linux.orig/arch/x86/kernel/alternative.c
+++ linux/arch/x86/kernel/alternative.c
@@ -424,9 +424,17 @@ void __init alternative_instructions(voi
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);

@@ -466,9 +474,6 @@ void __init alternative_instructions(voi
(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
+++ linux/arch/x86/kernel/cpu/mcheck/mce_64.c
@@ -699,20 +699,6 @@ static struct miscdevice mce_log_device
&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/include/asm-x86/mce.h
===================================================================
--- linux.orig/include/asm-x86/mce.h
+++ linux/include/asm-x86/mce.h
@@ -113,8 +113,6 @@ extern void mcheck_init(struct cpuinfo_x
#else
#define mcheck_init(c) do { } while (0)
#endif
-extern void stop_mce(void);
-extern void restart_mce(void);

#endif /* __KERNEL__ */

Index: linux/arch/x86/kernel/cpu/mcheck/mce_32.c
===================================================================
--- linux.orig/arch/x86/kernel/cpu/mcheck/mce_32.c
+++ linux/arch/x86/kernel/cpu/mcheck/mce_32.c
@@ -61,20 +61,6 @@ void mcheck_init(struct cpuinfo_x86 *c)
}
}

-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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