2 files changed, 17 insertions, 4 deletions

diff --git a/Documentation/x86_64/boot-options.txt b/Documentation/x86_64/boot-options.txt
index 476c0c22fbb7..678e8f192db2 100644
--- a/Documentation/x86_64/boot-options.txt
+++ b/Documentation/x86_64/boot-options.txt
@@ -6,6 +6,11 @@ only the AMD64 specific ones are listed here.
 Machine check
 
    mce=off disable machine check
+   mce=bootlog Enable logging of machine checks left over from booting.
+               Disabled by default because some BIOS leave bogus ones.
+               If your BIOS doesn't do that it's a good idea to enable though
+               to make sure you log even machine check events that result
+               in a reboot.
 
    nomce (for compatibility with i386): same as mce=off
 
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index 3b267c91bb0c..8aa56736cde3 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -36,6 +36,7 @@ static unsigned long bank[NR_BANKS] = { [0 ... NR_BANKS-1] = ~0UL };
 static unsigned long console_logged;
 static int notify_user;
 static int rip_msr;
+static int mce_bootlog;
 
 /*
  * Lockless MCE logging infrastructure.
@@ -197,10 +198,11 @@ void do_machine_check(struct pt_regs * regs, long error_code)
                         rdmsrl(MSR_IA32_MC0_ADDR + i*4, m.addr);
 
                 mce_get_rip(&m, regs);
-                if (error_code != -1)
+                if (error_code >= 0)
                         rdtscll(m.tsc);
                 wrmsrl(MSR_IA32_MC0_STATUS + i*4, 0);
-                mce_log(&m);
+                if (error_code != -2)
+                        mce_log(&m);
 
                 /* Did this bank cause the exception? */
                 /* Assume that the bank with uncorrectable errors did it,
@@ -315,7 +317,7 @@ static void mce_init(void *dummy)
 
         /* Log the machine checks left over from the previous reset.
            This also clears all registers */
-        do_machine_check(NULL, -1);
+        do_machine_check(NULL, mce_bootlog ? -1 : -2);
 
         set_in_cr4(X86_CR4_MCE);
 
@@ -476,11 +478,17 @@ static int __init mcheck_disable(char *str)
 }
 
 /* mce=off disables machine check. Note you can reenable it later
-   using sysfs */
+   using sysfs.
+   mce=bootlog Log MCEs from before booting. Disabled by default to work
+   around buggy BIOS that leave bogus MCEs.  */
 static int __init mcheck_enable(char *str)
 {
+        if (*str == '=')
+                str++;
         if (!strcmp(str, "off"))
                 mce_dont_init = 1;
+        else if (!strcmp(str, "bootlog"))
+                mce_bootlog = 1;
         else
                 printk("mce= argument %s ignored. Please use /sys", str); 
         return 0;