[RFC PATCH 1/7] static_call: get rid of static_call_cond()

@@ -991,7 +991,7 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
 	if (cpuc->txn_flags & PERF_PMU_TXN_ADD)
 		n0 -= cpuc->n_txn;
 
-	static_call_cond(x86_pmu_start_scheduling)(cpuc);
+	static_call(x86_pmu_start_scheduling)(cpuc);
 
 	for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) {
 		c = cpuc->event_constraint[i];

@@ -1090,7 +1090,7 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
 	 */
 	if (!unsched && assign) {
 		for (i = 0; i < n; i++)
-			static_call_cond(x86_pmu_commit_scheduling)(cpuc, i, assign[i]);
+			static_call(x86_pmu_commit_scheduling)(cpuc, i, assign[i]);
 	} else {
 		for (i = n0; i < n; i++) {
 			e = cpuc->event_list[i];

@@ -1098,13 +1098,13 @@ int x86_schedule_events(struct cpu_hw_events *cpuc, int n, int *assign)
 			/*
 			 * release events that failed scheduling
 			 */
-			static_call_cond(x86_pmu_put_event_constraints)(cpuc, e);
+			static_call(x86_pmu_put_event_constraints)(cpuc, e);
 
 			cpuc->event_constraint[i] = NULL;
 		}
 	}
 
-	static_call_cond(x86_pmu_stop_scheduling)(cpuc);
+	static_call(x86_pmu_stop_scheduling)(cpuc);
 
 	return unsched ? -EINVAL : 0;
 }

@@ -1217,7 +1217,7 @@ static inline void x86_assign_hw_event(struct perf_event *event,
 	hwc->last_cpu = smp_processor_id();
 	hwc->last_tag = ++cpuc->tags[i];
 
-	static_call_cond(x86_pmu_assign)(event, idx);
+	static_call(x86_pmu_assign)(event, idx);
 
 	switch (hwc->idx) {
 	case INTEL_PMC_IDX_FIXED_BTS:

@@ -1494,7 +1494,7 @@ static int x86_pmu_add(struct perf_event *event, int flags)
 	 * This is before x86_pmu_enable() will call x86_pmu_start(),
 	 * so we enable LBRs before an event needs them etc..
 	 */
-	static_call_cond(x86_pmu_add)(event);
+	static_call(x86_pmu_add)(event);
 
 	ret = 0;
 out:

@@ -1647,7 +1647,7 @@ static void x86_pmu_del(struct perf_event *event, int flags)
 	if (i >= cpuc->n_events - cpuc->n_added)
 		--cpuc->n_added;
 
-	static_call_cond(x86_pmu_put_event_constraints)(cpuc, event);
+	static_call(x86_pmu_put_event_constraints)(cpuc, event);
 
 	/* Delete the array entry. */
 	while (++i < cpuc->n_events) {

@@ -1667,7 +1667,7 @@ static void x86_pmu_del(struct perf_event *event, int flags)
 	 * This is after x86_pmu_stop(); so we disable LBRs after any
 	 * event can need them etc..
 	 */
-	static_call_cond(x86_pmu_del)(event);
+	static_call(x86_pmu_del)(event);
 }
 
 int x86_pmu_handle_irq(struct pt_regs *regs)

@@ -2638,13 +2638,13 @@ static const struct attribute_group *x86_pmu_attr_groups[] = {
 
 static void x86_pmu_sched_task(struct perf_event_context *ctx, bool sched_in)
 {
-	static_call_cond(x86_pmu_sched_task)(ctx, sched_in);
+	static_call(x86_pmu_sched_task)(ctx, sched_in);
 }
 
 static void x86_pmu_swap_task_ctx(struct perf_event_context *prev,
 				  struct perf_event_context *next)
 {
-	static_call_cond(x86_pmu_swap_task_ctx)(prev, next);
+	static_call(x86_pmu_swap_task_ctx)(prev, next);
 }
 
 void perf_check_microcode(void)

@@ -1914,12 +1914,12 @@ static inline bool kvm_irq_is_postable(struct kvm_lapic_irq *irq)
 
 static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu)
 {
-	static_call_cond(kvm_x86_vcpu_blocking)(vcpu);
+	static_call(kvm_x86_vcpu_blocking)(vcpu);
 }
 
 static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu)
 {
-	static_call_cond(kvm_x86_vcpu_unblocking)(vcpu);
+	static_call(kvm_x86_vcpu_unblocking)(vcpu);
 }
 
 static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {}

@@ -150,7 +150,7 @@ void __kvm_migrate_timers(struct kvm_vcpu *vcpu)
 {
 	__kvm_migrate_apic_timer(vcpu);
 	__kvm_migrate_pit_timer(vcpu);
-	static_call_cond(kvm_x86_migrate_timers)(vcpu);
+	static_call(kvm_x86_migrate_timers)(vcpu);
 }
 
 bool kvm_arch_irqfd_allowed(struct kvm *kvm, struct kvm_irqfd *args)

@@ -11418,7 +11418,7 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
 		__x86_set_memory_region(kvm, TSS_PRIVATE_MEMSLOT, 0, 0);
 		mutex_unlock(&kvm->slots_lock);
 	}
-	static_call_cond(kvm_x86_vm_destroy)(kvm);
+	static_call(kvm_x86_vm_destroy)(kvm);
 	kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
 	kvm_pic_destroy(kvm);
 	kvm_ioapic_destroy(kvm);

@@ -12038,7 +12038,7 @@ bool kvm_arch_can_dequeue_async_page_present(struct kvm_vcpu *vcpu)
 void kvm_arch_start_assignment(struct kvm *kvm)
 {
 	if (atomic_inc_return(&kvm->arch.assigned_device_count) == 1)
-		static_call_cond(kvm_x86_start_assignment)(kvm);
+		static_call(kvm_x86_start_assignment)(kvm);
 }
 EXPORT_SYMBOL_GPL(kvm_arch_start_assignment);
 

@@ -92,23 +92,16 @@
  *
  *   where the argument evaludation also depends on the pointer value.
  *
- *   When calling a static_call that can be NULL, use:
- *
- *     static_call_cond(name)(arg1);
- *
- *   which will include the required value tests to avoid NULL-pointer
- *   dereferences.
- *
  *   To query which function is currently set to be called, use:
  *
  *   func = static_call_query(name);
  *
  *
- * DEFINE_STATIC_CALL_RET0 / __static_call_return0:
+ * DEFINE_STATIC_CALL_RET0:
  *
- *   Just like how DEFINE_STATIC_CALL_NULL() / static_call_cond() optimize the
- *   conditional void function call, DEFINE_STATIC_CALL_RET0 /
- *   __static_call_return0 optimize the do nothing return 0 function.
+ *   Just like how DEFINE_STATIC_CALL_NULL() optimizes the conditional void
+ *   function call, DEFINE_STATIC_CALL_RET0 optimizes the do nothing return 0
+ *   function.
  *
  *   This feature is strictly UB per the C standard (since it casts a function
  *   pointer to a different signature) and relies on the architecture ABI to

@@ -196,8 +189,6 @@ extern long __static_call_return0(void);
 	};								\
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
-#define static_call_cond(name)	(void)__static_call(name)
-
 #define EXPORT_STATIC_CALL(name)					\
 	EXPORT_SYMBOL(STATIC_CALL_KEY(name));				\
 	EXPORT_SYMBOL(STATIC_CALL_TRAMP(name))

@@ -232,8 +223,6 @@ static inline int static_call_init(void) { return 0; }
 	ARCH_DEFINE_STATIC_CALL_NULL_TRAMP(name)
 
 
-#define static_call_cond(name)	(void)__static_call(name)
-
 static inline
 void __static_call_update(struct static_call_key *key, void *tramp, void *func)
 {

@@ -275,6 +264,8 @@ static inline long __static_call_return0(void)
 	return 0;
 }
 
+static inline void __static_call_nop(void) { }
+
 #define __DEFINE_STATIC_CALL(name, _func, _func_init)			\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\

@@ -284,37 +275,13 @@ static inline long __static_call_return0(void)
 #define DEFINE_STATIC_CALL_NULL(name, _func)				\
 	DECLARE_STATIC_CALL(name, _func);				\
 	struct static_call_key STATIC_CALL_KEY(name) = {		\
-		.func = NULL,						\
+		.func = (void *)__static_call_nop,			\
 	}
 
-static inline void __static_call_nop(void) { }
-
-/*
- * This horrific hack takes care of two things:
- *
- *  - it ensures the compiler will only load the function pointer ONCE,
- *    which avoids a reload race.
- *
- *  - it ensures the argument evaluation is unconditional, similar
- *    to the HAVE_STATIC_CALL variant.
- *
- * Sadly current GCC/Clang (10 for both) do not optimize this properly
- * and will emit an indirect call for the NULL case :-(
- */
-#define __static_call_cond(name)					\
-({									\
-	void *func = READ_ONCE(STATIC_CALL_KEY(name).func);		\
-	if (!func)							\
-		func = &__static_call_nop;				\
-	(typeof(STATIC_CALL_TRAMP(name))*)func;				\
-})
-
-#define static_call_cond(name)	(void)__static_call_cond(name)
-
 static inline
 void __static_call_update(struct static_call_key *key, void *tramp, void *func)
 {
-	WRITE_ONCE(key->func, func);
+	WRITE_ONCE(key->func, func ?: (void *)&__static_call_nop);
 }
 
 static inline int static_call_text_reserved(void *start, void *end)