perf/core: Use static_call to optimize perf_guest_info_callbacks

Use static_call to optimize perf's guest callbacks on arm64 and x86,
which are now the only architectures that define the callbacks.  Use
DEFINE_STATIC_CALL_RET0 as the default/NULL for all guest callbacks, as
the callback semantics are that a return value '0' means "not in guest".

static_call obviously avoids the overhead of CONFIG_RETPOLINE=y, but is
also advantageous versus other solutions, e.g. per-cpu callbacks, in that
a per-cpu memory load is not needed to detect the !guest case.

Based on code from Peter and Like.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20211111020738.2512932-10-seanjc@google.com

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index ea47ef616ee04203a9dd3d5d401340522fb1f586..0ac7d867ca0ca8fdb0997baa298cec828cd09522 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1244,40 +1244,22 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
 
 #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)
-{
-       /*
-        * Callbacks are RCU-protected and must be READ_ONCE to avoid reloading
-        * the callbacks between a !NULL check and dereferences, to ensure
-        * pending stores/changes to the callback pointers are visible before a
-        * non-NULL perf_guest_cbs is visible to readers, and to prevent a
-        * module from unloading callbacks while readers are active.
-        */
-       return rcu_dereference(perf_guest_cbs);
-}
+
+DECLARE_STATIC_CALL(__perf_guest_state, *perf_guest_cbs->state);
+DECLARE_STATIC_CALL(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
+DECLARE_STATIC_CALL(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
+
 static inline unsigned int perf_guest_state(void)
 {
-       struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-       return guest_cbs ? guest_cbs->state() : 0;
+       return static_call(__perf_guest_state)();
 }
 static inline unsigned long perf_guest_get_ip(void)
 {
-       struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-       /*
-        * Arbitrarily return '0' in the unlikely scenario that the callbacks
-        * are unregistered between checking guest state and getting the IP.
-        */
-       return guest_cbs ? guest_cbs->get_ip() : 0;
+       return static_call(__perf_guest_get_ip)();
 }
 static inline unsigned int perf_guest_handle_intel_pt_intr(void)
 {
-       struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-       if (guest_cbs && guest_cbs->handle_intel_pt_intr)
-               return guest_cbs->handle_intel_pt_intr();
-       return 0;
+       return static_call(__perf_guest_handle_intel_pt_intr)();
 }
 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);

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5a3502cd5362c5c9ce421a197e51ff20283a64f9..3b3297a5722851950e03d7b23a89819ef69a019e 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6524,12 +6524,23 @@ static void perf_pending_event(struct irq_work *entry)
 #ifdef CONFIG_GUEST_PERF_EVENTS
 struct perf_guest_info_callbacks __rcu *perf_guest_cbs;
 
+DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state);
+DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip);
+DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr);
+
 void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 {
        if (WARN_ON_ONCE(rcu_access_pointer(perf_guest_cbs)))
                return;
 
        rcu_assign_pointer(perf_guest_cbs, cbs);
+       static_call_update(__perf_guest_state, cbs->state);
+       static_call_update(__perf_guest_get_ip, cbs->get_ip);
+
+       /* Implementing ->handle_intel_pt_intr is optional. */
+       if (cbs->handle_intel_pt_intr)
+               static_call_update(__perf_guest_handle_intel_pt_intr,
+                                  cbs->handle_intel_pt_intr);
 }
 EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
 
@@ -6539,6 +6550,10 @@ void perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
                return;
 
        rcu_assign_pointer(perf_guest_cbs, NULL);
+       static_call_update(__perf_guest_state, (void *)&__static_call_return0);
+       static_call_update(__perf_guest_get_ip, (void *)&__static_call_return0);
+       static_call_update(__perf_guest_handle_intel_pt_intr,
+                          (void *)&__static_call_return0);
        synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);