perf: Force architectures to opt-in to guest callbacks

Introduce GUEST_PERF_EVENTS and require architectures to select it to allow registering and using guest callbacks in perf. This will hopefully make it more difficult for new architectures to add useless "support" for guest callbacks, e.g. via copy+paste. Stubbing out the helpers has the happy bonus of avoiding a load of perf_guest_cbs when GUEST_PERF_EVENTS=n on arm64/x86. 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]
torvalds · Nov 17, 2021 · 2aef6f3 · 2aef6f3
1 parent 1c34305
commit 2aef6f3
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diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
@@ -39,6 +39,7 @@ menuconfig KVM
  select HAVE_KVM_IRQ_BYPASS
  select HAVE_KVM_VCPU_RUN_PID_CHANGE
  select SCHED_INFO
+ select GUEST_PERF_EVENTS if PERF_EVENTS
  help
  Support hosting virtualized guest machines.
 

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
@@ -36,6 +36,7 @@ config KVM
  select KVM_MMIO
  select SCHED_INFO
  select PERF_EVENTS
+ select GUEST_PERF_EVENTS
  select HAVE_KVM_MSI
  select HAVE_KVM_CPU_RELAX_INTERCEPT
  select HAVE_KVM_NO_POLL

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
@@ -23,6 +23,7 @@ config XEN_PV
  select PARAVIRT_XXL
  select XEN_HAVE_PVMMU
  select XEN_HAVE_VPMU
+ select GUEST_PERF_EVENTS
  help
  Support running as a Xen PV guest.
 

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
@@ -1242,6 +1242,7 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
  enum perf_bpf_event_type type,
  u16 flags);
 
+#ifdef CONFIG_GUEST_PERF_EVENTS
 extern struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
 {
@@ -1280,6 +1281,11 @@ static inline unsigned int perf_guest_handle_intel_pt_intr(void)
 }
 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);
+#else
+static inline unsigned int perf_guest_state(void) { return 0; }
+static inline unsigned long perf_guest_get_ip(void) { return 0; }
+static inline unsigned int perf_guest_handle_intel_pt_intr(void) { return 0; }
+#endif /* CONFIG_GUEST_PERF_EVENTS */
 
 extern void perf_event_exec(void);
 extern void perf_event_comm(struct task_struct *tsk, bool exec);

diff --git a/init/Kconfig b/init/Kconfig
@@ -1804,6 +1804,10 @@ config HAVE_PERF_EVENTS
  help
  See tools/perf/design.txt for details.
 
+config GUEST_PERF_EVENTS
+ bool
+ depends on HAVE_PERF_EVENTS
+
 config PERF_USE_VMALLOC
  bool
  help

diff --git a/kernel/events/core.c b/kernel/events/core.c
@@ -6521,6 +6521,7 @@ static void perf_pending_event(struct irq_work *entry)
  perf_swevent_put_recursion_context(rctx);
 }
 
+#ifdef CONFIG_GUEST_PERF_EVENTS
 struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 
 void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
@@ -6541,6 +6542,7 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
  synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
+#endif
 
 static void
 perf_output_sample_regs(struct perf_output_handle *handle,