Messages in this thread Patch in this message | | | From | Andi Kleen <> | Subject | [PATCH] [2/10] x86: MCE: Don't disable machine checks during code patching | Date | Thu, 12 Feb 2009 13:39:27 +0100 (CET) |
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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@linux.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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