x86 mtrr: Remove (noop) lock_cpu_hotplug().

CPUs coming online sync themselves with current MTRR state at an
appropriate point anyway.

It's not actually possible to have a newly booted CPU immediately have
in-sync MTRR state anyway. It has to be synced up as part of normal
CPU bootstrap procedure. Which is what we do.

Signed-off-by: Keir Fraser <keir.fraser@citrix.com>

xen/arch/x86/cpu/mtrr/main.c

@@ -365,8 +365,6 @@ int mtrr_add_page(unsigned long base, unsigned long size,
 	error = -EINVAL;
 	replace = -1;
 
-	/* No CPU hotplug when we change MTRR entries */
-	lock_cpu_hotplug();
 	/*  Search for existing MTRR  */
 	mutex_lock(&mtrr_mutex);
 	for (i = 0; i < num_var_ranges; ++i) {
@@ -422,7 +420,6 @@ int mtrr_add_page(unsigned long base, unsigned long size,
 	error = i;
  out:
 	mutex_unlock(&mtrr_mutex);
-	unlock_cpu_hotplug();
 	return error;
 }
 
@@ -511,8 +508,6 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
 		return -ENXIO;
 
 	max = num_var_ranges;
-	/* No CPU hotplug when we change MTRR entries */
-	lock_cpu_hotplug();
 	mutex_lock(&mtrr_mutex);
 	if (reg < 0) {
 		/*  Search for existing MTRR  */
@@ -553,7 +548,6 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
 	error = reg;
  out:
 	mutex_unlock(&mtrr_mutex);
-	unlock_cpu_hotplug();
 	return error;
 }
 /**

xen/include/xen/smp.h

@@ -61,10 +61,6 @@ static inline int on_each_cpu(
 
 #define smp_processor_id() raw_smp_processor_id()
 
-/* No Xen contexts can be preempted by CPU hotplug. */
-#define lock_cpu_hotplug() ((void)0)
-#define unlock_cpu_hotplug() ((void)0)
-
 int alloc_cpu_id(void);
 
 #endif /* __XEN_SMP_H__ */