perf: Stop pretending that perf can handle multiple guest callbacks

Drop the 'int' return value from the perf (un)register callbacks helpers
and stop pretending perf can support multiple callbacks.  The 'int'
returns are not future proofing anything as none of the callers take
action on an error.  It's also not obvious that there will ever be
co-tenant hypervisors, and if there are, that allowing multiple callbacks
to be registered is desirable or even correct.

Opportunistically rename callbacks=>cbs in the affected declarations to
match their definitions.

No functional change intended.

Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: sean-jc

arch/arm64/include/asm/kvm_host.h

@@ -675,8 +675,8 @@ unsigned long kvm_mmio_read_buf(const void *buf, unsigned int len);
 int kvm_handle_mmio_return(struct kvm_vcpu *vcpu);
 int io_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa);
 
-int kvm_perf_init(void);
-int kvm_perf_teardown(void);
+void kvm_perf_init(void);
+void kvm_perf_teardown(void);
 
 long kvm_hypercall_pv_features(struct kvm_vcpu *vcpu);
 gpa_t kvm_init_stolen_time(struct kvm_vcpu *vcpu);

arch/arm64/kvm/perf.c

@@ -48,12 +48,12 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = {
 	.get_guest_ip	= kvm_get_guest_ip,
 };
 
-int kvm_perf_init(void)
+void kvm_perf_init(void)
 {
-	return perf_register_guest_info_callbacks(&kvm_guest_cbs);
+	perf_register_guest_info_callbacks(&kvm_guest_cbs);
 }
 
-int kvm_perf_teardown(void)
+void kvm_perf_teardown(void)
 {
-	return perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
+	perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
 }

include/linux/perf_event.h

@@ -1252,8 +1252,8 @@ static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
 	 */
 	return rcu_dereference(perf_guest_cbs);
 }
-extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
-extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
+extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
+extern void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs);
 
 extern void perf_event_exec(void);
 extern void perf_event_comm(struct task_struct *tsk, bool exec);
@@ -1497,10 +1497,10 @@ perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)	{ }
 static inline void
 perf_bp_event(struct perf_event *event, void *data)			{ }
 
-static inline int perf_register_guest_info_callbacks
-(struct perf_guest_info_callbacks *callbacks)				{ return 0; }
-static inline int perf_unregister_guest_info_callbacks
-(struct perf_guest_info_callbacks *callbacks)				{ return 0; }
+static inline void perf_register_guest_info_callbacks
+(struct perf_guest_info_callbacks *cbs)					{ }
+static inline void perf_unregister_guest_info_callbacks
+(struct perf_guest_info_callbacks *cbs)					{ }
 
 static inline void perf_event_mmap(struct vm_area_struct *vma)		{ }
 

kernel/events/core.c

@@ -6521,31 +6521,24 @@ static void perf_pending_event(struct irq_work *entry)
 		perf_swevent_put_recursion_context(rctx);
 }
 
-/*
- * We assume there is only KVM supporting the callbacks.
- * Later on, we might change it to a list if there is
- * another virtualization implementation supporting the callbacks.
- */
 struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 
-int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
+void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 {
 	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs)))
-		return -EBUSY;
+		return;
 
 	rcu_assign_pointer(perf_guest_cbs, cbs);
-	return 0;
 }
 EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
 
-int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
+void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 {
 	if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs) != cbs))
-		return -EINVAL;
+		return;
 
 	rcu_assign_pointer(perf_guest_cbs, NULL);
 	synchronize_rcu();
-	return 0;
 }
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);