perf/x86: Update rdpmc_always_available static key to the modern API

No changes in refcount semantics -- use DEFINE_STATIC_KEY_FALSE()
for initialization and replace:

  static_key_slow_inc|dec()   =>   static_branch_inc|dec()
  static_key_false()          =>   static_branch_unlikely()

Added a '_key' suffix to rdpmc_always_available, for better self-documentation.

Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: akpm@linux-foundation.org
Link: http://lkml.kernel.org/r/20180326210929.5244-5-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/events/core.c

@@ -48,7 +48,7 @@ DEFINE_PER_CPU(struct cpu_hw_events, cpu_hw_events) = {
 	.enabled = 1,
 };
 
-struct static_key rdpmc_always_available = STATIC_KEY_INIT_FALSE;
+DEFINE_STATIC_KEY_FALSE(rdpmc_always_available_key);
 
 u64 __read_mostly hw_cache_event_ids
 				[PERF_COUNT_HW_CACHE_MAX]
@@ -2206,9 +2206,9 @@ static ssize_t set_attr_rdpmc(struct device *cdev,
 		 * but only root can trigger it, so it's okay.
 		 */
 		if (val == 2)
-			static_key_slow_inc(&rdpmc_always_available);
+			static_branch_inc(&rdpmc_always_available_key);
 		else
-			static_key_slow_dec(&rdpmc_always_available);
+			static_branch_dec(&rdpmc_always_available_key);
 		on_each_cpu(refresh_pce, NULL, 1);
 	}
 

arch/x86/include/asm/mmu_context.h

@@ -24,11 +24,12 @@ static inline void paravirt_activate_mm(struct mm_struct *prev,
 #endif	/* !CONFIG_PARAVIRT */
 
 #ifdef CONFIG_PERF_EVENTS
-extern struct static_key rdpmc_always_available;
+
+DECLARE_STATIC_KEY_FALSE(rdpmc_always_available_key);
 
 static inline void load_mm_cr4(struct mm_struct *mm)
 {
-	if (static_key_false(&rdpmc_always_available) ||
+	if (static_branch_unlikely(&rdpmc_always_available_key) ||
 	    atomic_read(&mm->context.perf_rdpmc_allowed))
 		cr4_set_bits(X86_CR4_PCE);
 	else