[PATCH] i386: Allow boot-time disable of SMP altinstructions

Add "noreplace-smp" to disable SMP instruction replacement.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>

2 files changed, 25 insertions, 4 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 94ce0d20253d..242b3a09b6ce 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1164,6 +1164,9 @@ and is between 256 and 4096 characters. It is defined in the file
 
         nomce           [IA-32] Machine Check Exception
 
+        noreplace-smp   [IA-32,SMP] Don't replace SMP instructions
+                        with UP alternatives
+
         noresidual      [PPC] Don't use residual data on PReP machines.
 
         noresume        [SWSUSP] Disables resume and restores original swap
@@ -1569,6 +1572,9 @@ and is between 256 and 4096 characters. It is defined in the file
         smart2=         [HW]
                         Format: <io1>[,<io2>[,...,<io8>]]
 
+        smp-alt-once    [IA-32,SMP] On a hotplug CPU system, only
+                        attempt to substitute SMP alternatives once at boot.
+
         snd-ad1816a=    [HW,ALSA]
 
         snd-ad1848=     [HW,ALSA]
diff --git a/arch/i386/kernel/alternative.c b/arch/i386/kernel/alternative.c
index f09635408049..9b8e85a8edec 100644
--- a/arch/i386/kernel/alternative.c
+++ b/arch/i386/kernel/alternative.c
@@ -5,6 +5,7 @@
 #include <asm/alternative.h>
 #include <asm/sections.h>
 
+static int noreplace_smp     = 0;
 static int smp_alt_once      = 0;
 static int debug_alternative = 0;
 
@@ -13,15 +14,23 @@ static int __init bootonly(char *str)
         smp_alt_once = 1;
         return 1;
 }
+__setup("smp-alt-boot", bootonly);
+
 static int __init debug_alt(char *str)
 {
         debug_alternative = 1;
         return 1;
 }
-
-__setup("smp-alt-boot", bootonly);
 __setup("debug-alternative", debug_alt);
 
+static int __init setup_noreplace_smp(char *str)
+{
+        noreplace_smp = 1;
+        return 1;
+}
+__setup("noreplace-smp", setup_noreplace_smp);
+
+
 #define DPRINTK(fmt, args...) if (debug_alternative) \
         printk(KERN_DEBUG fmt, args)
 
@@ -185,6 +194,9 @@ static void alternatives_smp_unlock(u8 **start, u8 **end, u8 *text, u8 *text_end
 {
         u8 **ptr;
 
+        if (noreplace_smp)
+                return;
+
         for (ptr = start; ptr < end; ptr++) {
                 if (*ptr < text)
                         continue;
@@ -219,6 +231,9 @@ void alternatives_smp_module_add(struct module *mod, char *name,
         struct smp_alt_module *smp;
         unsigned long flags;
 
+        if (noreplace_smp)
+                return;
+
         if (smp_alt_once) {
                 if (boot_cpu_has(X86_FEATURE_UP))
                         alternatives_smp_unlock(locks, locks_end,
@@ -253,7 +268,7 @@ void alternatives_smp_module_del(struct module *mod)
         struct smp_alt_module *item;
         unsigned long flags;
 
-        if (smp_alt_once)
+        if (smp_alt_once || noreplace_smp)
                 return;
 
         spin_lock_irqsave(&smp_alt, flags);
@@ -284,7 +299,7 @@ void alternatives_smp_switch(int smp)
         return;
 #endif
 
-        if (smp_alt_once)
+        if (noreplace_smp || smp_alt_once)
                 return;
         BUG_ON(!smp && (num_online_cpus() > 1));