[PATCH v2 04/13] perf: Stop pretending that perf can handle multiple guest callbacks

[Sean Christopherson <seanjc@google.com>]

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.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/include/asm/kvm_host.h |  4 ++--
 arch/arm64/kvm/perf.c             |  8 ++++----
 arch/x86/kvm/x86.c                |  2 +-
 include/linux/perf_event.h        | 11 +++++------
 kernel/events/core.c              | 14 +++-----------
 5 files changed, 15 insertions(+), 24 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 41911585ae0c..ed940aec89e0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -670,8 +670,8 @@ 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);
diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c
index 151c31fb9860..039fe59399a2 100644
--- a/arch/arm64/kvm/perf.c
+++ b/arch/arm64/kvm/perf.c
@@ -48,15 +48,15 @@ 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)
 {
 	if (kvm_pmu_probe_pmuver() != 0xf && !is_protected_kvm_enabled())
 		static_branch_enable(&kvm_arm_pmu_available);
 
-	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();
 }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ffc6c2d73508..bae951344e28 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11092,7 +11092,7 @@ int kvm_arch_hardware_setup(void *opaque)
 
 void kvm_arch_hardware_unsetup(void)
 {
-	perf_unregister_guest_info_callbacks(&kvm_guest_cbs);
+	perf_unregister_guest_info_callbacks();
 	kvm_guest_cbs.handle_intel_pt_intr = NULL;
 
 	static_call(kvm_x86_hardware_unsetup)();
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 6b0405e578c1..2b77e2154b61 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1245,8 +1245,8 @@ static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
 	/* Prevent reloading between a !NULL check and dereferences. */
 	return READ_ONCE(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 *callbacks);
+extern void perf_unregister_guest_info_callbacks(void);
 
 extern void perf_event_exec(void);
 extern void perf_event_comm(struct task_struct *tsk, bool exec);
@@ -1489,10 +1489,9 @@ 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 *callbacks)				{ }
+static inline void perf_unregister_guest_info_callbacks(void)		{ }
 
 static inline void perf_event_mmap(struct vm_area_struct *vma)		{ }
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2126f6327321..1be95d9ace46 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6482,29 +6482,21 @@ 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 *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(perf_guest_cbs))
-		return -EBUSY;
+		return;
 
 	WRITE_ONCE(perf_guest_cbs, cbs);
 	synchronize_rcu();
-	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(void)
 {
 	WRITE_ONCE(perf_guest_cbs, NULL);
 	synchronize_rcu();
-	return 0;
 }
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
 
-- 
2.33.0.259.gc128427fd7-goog