x86/perf: Use static_call for x86_pmu.guest_get_msrs

Clean up that CONFIG_RETPOLINE crud and replace the
indirect call x86_pmu.guest_get_msrs with static_call().
Reported-by: Nkernel test robot <lkp@intel.com>
Suggested-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NLike Xu <like.xu@linux.intel.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210125121458.181635-1-like.xu@linux.intel.com

arch/x86/events/core.c

@@ -81,6 +81,8 @@ DEFINE_STATIC_CALL_NULL(x86_pmu_swap_task_ctx, *x86_pmu.swap_task_ctx);
 DEFINE_STATIC_CALL_NULL(x86_pmu_drain_pebs,   *x86_pmu.drain_pebs);
 DEFINE_STATIC_CALL_NULL(x86_pmu_pebs_aliases, *x86_pmu.pebs_aliases);
 
+DEFINE_STATIC_CALL_NULL(x86_pmu_guest_get_msrs,  *x86_pmu.guest_get_msrs);
+
 u64 __read_mostly hw_cache_event_ids
 				[PERF_COUNT_HW_CACHE_MAX]
 				[PERF_COUNT_HW_CACHE_OP_MAX]
@@ -665,6 +667,12 @@ void x86_pmu_disable_all(void)
 	}
 }
 
+struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
+{
+	return static_call(x86_pmu_guest_get_msrs)(nr);
+}
+EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
+
 /*
  * There may be PMI landing after enabled=0. The PMI hitting could be before or
  * after disable_all.
@@ -1923,6 +1931,8 @@ static void x86_pmu_static_call_update(void)
 
 	static_call_update(x86_pmu_drain_pebs, x86_pmu.drain_pebs);
 	static_call_update(x86_pmu_pebs_aliases, x86_pmu.pebs_aliases);
+
+	static_call_update(x86_pmu_guest_get_msrs, x86_pmu.guest_get_msrs);
 }
 
 static void _x86_pmu_read(struct perf_event *event)
@@ -1930,6 +1940,13 @@ static void _x86_pmu_read(struct perf_event *event)
 	x86_perf_event_update(event);
 }
 
+static inline struct perf_guest_switch_msr *
+perf_guest_get_msrs_nop(int *nr)
+{
+	*nr = 0;
+	return NULL;
+}
+
 static int __init init_hw_perf_events(void)
 {
 	struct x86_pmu_quirk *quirk;
@@ -2001,6 +2018,9 @@ static int __init init_hw_perf_events(void)
 	if (!x86_pmu.read)
 		x86_pmu.read = _x86_pmu_read;
 
+	if (!x86_pmu.guest_get_msrs)
+		x86_pmu.guest_get_msrs = perf_guest_get_msrs_nop;
+
 	x86_pmu_static_call_update();
 
 	/*

arch/x86/events/intel/core.c

@@ -3680,26 +3680,6 @@ static int intel_pmu_hw_config(struct perf_event *event)
 	return 0;
 }
 
-#ifdef CONFIG_RETPOLINE
-static struct perf_guest_switch_msr *core_guest_get_msrs(int *nr);
-static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr);
-#endif
-
-struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
-{
-#ifdef CONFIG_RETPOLINE
-	if (x86_pmu.guest_get_msrs == intel_guest_get_msrs)
-		return intel_guest_get_msrs(nr);
-	else if (x86_pmu.guest_get_msrs == core_guest_get_msrs)
-		return core_guest_get_msrs(nr);
-#endif
-	if (x86_pmu.guest_get_msrs)
-		return x86_pmu.guest_get_msrs(nr);
-	*nr = 0;
-	return NULL;
-}
-EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
-
 static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr)
 {
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);

arch/x86/include/asm/perf_event.h

@@ -483,11 +483,7 @@ static inline void perf_check_microcode(void) { }
 extern struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
 extern int x86_perf_get_lbr(struct x86_pmu_lbr *lbr);
 #else
-static inline struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
-{
-	*nr = 0;
-	return NULL;
-}
+struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr);
 static inline int x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
 {
 	return -1;