x86, 32-bit: trim memory not covered by wb mtrrs

[deliverable/linux.git] / arch / x86 / kernel / alternative.c

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index cdc43242da92ed3e272982216f5d01ef23b89b22..318a4f9b7ececcaec148e77089234f16bee309c5 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -273,6 +273,7 @@ struct smp_alt_module {
 };
 static LIST_HEAD(smp_alt_modules);
 static DEFINE_SPINLOCK(smp_alt);
+static int smp_mode = 1;       /* protected by smp_alt */
 
 void alternatives_smp_module_add(struct module *mod, char *name,
                                 void *locks, void *locks_end,
@@ -354,7 +355,14 @@ void alternatives_smp_switch(int smp)
        BUG_ON(!smp && (num_online_cpus() > 1));
 
        spin_lock_irqsave(&smp_alt, flags);
-       if (smp) {
+
+       /*
+        * Avoid unnecessary switches because it forces JIT based VMs to
+        * throw away all cached translations, which can be quite costly.
+        */
+       if (smp == smp_mode) {
+               /* nothing */
+       } else if (smp) {
                printk(KERN_INFO "SMP alternatives: switching to SMP code\n");
                clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
                clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
@@ -369,6 +377,7 @@ void alternatives_smp_switch(int smp)
                        alternatives_smp_unlock(mod->locks, mod->locks_end,
                                                mod->text, mod->text_end);
        }
+       smp_mode = smp;
        spin_unlock_irqrestore(&smp_alt, flags);
 }
 
@@ -441,7 +450,10 @@ void __init alternative_instructions(void)
                alternatives_smp_module_add(NULL, "core kernel",
                                            __smp_locks, __smp_locks_end,
                                            _text, _etext);
-               alternatives_smp_switch(0);
+
+               /* Only switch to UP mode if we don't immediately boot others */
+               if (num_possible_cpus() == 1 || setup_max_cpus <= 1)
+                       alternatives_smp_switch(0);
        }
 #endif
        apply_paravirt(__parainstructions, __parainstructions_end);