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@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/include/asm/mce.h b/arch/x86/include/asm/mce.h
index 32c6e17b960b7aed994078dc1d5c1fb4e547b2a4..5522273a3ad833610557f8a8592862ec28bda17e 100644 (file)
--- a/arch/x86/include/asm/mce.h
+++ b/arch/x86/include/asm/mce.h
@@ -120,8 +120,6 @@ extern void mcheck_init(struct cpuinfo_x86 *c);
 #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 */

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index a84ac7b570e6bb4582788da74a4c570e28fd65e9..5b8394a3a6b25a20ac49d7c113098385f06e5748 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -414,9 +414,17 @@ void __init alternative_instructions(void)
           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 @@ void __init alternative_instructions(void)
                                (unsigned long)__smp_locks_end);
 
        restart_nmi();
-#ifdef CONFIG_X86_MCE
-       restart_mce();
-#endif
 }
 
 /**

diff --git a/arch/x86/kernel/cpu/mcheck/mce_32.c b/arch/x86/kernel/cpu/mcheck/mce_32.c
index dfaebce3633e3f9b8415e79f29ad9f012276825a..3552119b091da51e65ce933c9852eee694920b9b 100644 (file)
--- a/arch/x86/kernel/cpu/mcheck/mce_32.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_32.c
@@ -60,20 +60,6 @@ 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;

diff --git a/arch/x86/kernel/cpu/mcheck/mce_64.c b/arch/x86/kernel/cpu/mcheck/mce_64.c
index 5ed80991ab9ecca2415b93f5f9907222ea0cbd52..25ccdbec86e2345e0ac77795c3d2308543efa32e 100644 (file)
--- a/arch/x86/kernel/cpu/mcheck/mce_64.c
+++ b/arch/x86/kernel/cpu/mcheck/mce_64.c
@@ -680,20 +680,6 @@ 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.
  */