[PATCH v2 07/13] perf/core: Use static_call to optimize perf_guest_info_callbacks

[Sean Christopherson]

From: Like Xu <like.xu@xxxxxxxxxxxxxxx>

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.

Suggested-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Originally-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Signed-off-by: Like Xu <like.xu@xxxxxxxxxxxxxxx>
Signed-off-by: Zhu Lingshan <lingshan.zhu@xxxxxxxxx>
[sean: split out patch, drop __weak, tweak updaters, rewrite changelog]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/arm64/kernel/perf_callchain.c | 31 +++++++++++++++---------
 arch/x86/events/core.c             | 38 ++++++++++++++++++++++--------
 arch/x86/events/intel/core.c       |  7 +++---
 include/linux/perf_event.h         |  9 +------
 kernel/events/core.c               |  2 ++
 5 files changed, 54 insertions(+), 33 deletions(-)

diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 274dc3e11b6d..18cf6e608778 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -5,6 +5,7 @@
  * Copyright (C) 2015 ARM Limited
  */
 #include <linux/perf_event.h>
+#include <linux/static_call.h>
 #include <linux/uaccess.h>
 
 #include <asm/pointer_auth.h>
@@ -99,12 +100,24 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
 }
 #endif /* CONFIG_COMPAT */
 
+DEFINE_STATIC_CALL_RET0(arm64_guest_state, *(perf_guest_cbs->state));
+DEFINE_STATIC_CALL_RET0(arm64_guest_get_ip, *(perf_guest_cbs->get_ip));
+
+void arch_perf_update_guest_cbs(struct perf_guest_info_callbacks *guest_cbs)
+{
+	if (guest_cbs) {
+		static_call_update(arm64_guest_state, guest_cbs->state);
+		static_call_update(arm64_guest_get_ip, guest_cbs->get_ip);
+	} else {
+		static_call_update(arm64_guest_state, (void *)&__static_call_return0);
+		static_call_update(arm64_guest_get_ip, (void *)&__static_call_return0);
+	}
+}
+
 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 			 struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state()) {
+	if (static_call(arm64_guest_state)()) {
 		/* We don't support guest os callchain now */
 		return;
 	}
@@ -149,10 +162,9 @@ static bool callchain_trace(void *data, unsigned long pc)
 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 			   struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
 	struct stackframe frame;
 
-	if (guest_cbs && guest_cbs->state()) {
+	if (static_call(arm64_guest_state)()) {
 		/* We don't support guest os callchain now */
 		return;
 	}
@@ -163,18 +175,15 @@ void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
 
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state())
-		return guest_cbs->get_ip();
+	if (static_call(arm64_guest_state)())
+		return static_call(arm64_guest_get_ip)();
 
 	return instruction_pointer(regs);
 }
 
 unsigned long perf_misc_flags(struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
+	unsigned int guest_state = static_call(arm64_guest_state)();
 	int misc = 0;
 
 	if (guest_state) {
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 3a7630fdd340..508a677edd8c 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -90,6 +90,29 @@ DEFINE_STATIC_CALL_NULL(x86_pmu_pebs_aliases, *x86_pmu.pebs_aliases);
  */
 DEFINE_STATIC_CALL_RET0(x86_pmu_guest_get_msrs, *x86_pmu.guest_get_msrs);
 
+DEFINE_STATIC_CALL_RET0(x86_guest_state, *(perf_guest_cbs->state));
+DEFINE_STATIC_CALL_RET0(x86_guest_get_ip, *(perf_guest_cbs->get_ip));
+DEFINE_STATIC_CALL_RET0(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+
+void arch_perf_update_guest_cbs(struct perf_guest_info_callbacks *guest_cbs)
+{
+	if (guest_cbs) {
+		static_call_update(x86_guest_state, guest_cbs->state);
+		static_call_update(x86_guest_get_ip, guest_cbs->get_ip);
+	} else {
+		static_call_update(x86_guest_state, (void *)&__static_call_return0);
+		static_call_update(x86_guest_get_ip, (void *)&__static_call_return0);
+	}
+
+	/* Implementing ->handle_intel_pt_intr is optional. */
+	if (guest_cbs && guest_cbs->handle_intel_pt_intr)
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   guest_cbs->handle_intel_pt_intr);
+	else
+		static_call_update(x86_guest_handle_intel_pt_intr,
+				   (void *)&__static_call_return0);
+}
+
 u64 __read_mostly hw_cache_event_ids
 				[PERF_COUNT_HW_CACHE_MAX]
 				[PERF_COUNT_HW_CACHE_OP_MAX]
@@ -2761,11 +2784,10 @@ static bool perf_hw_regs(struct pt_regs *regs)
 void
 perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
 	struct unwind_state state;
 	unsigned long addr;
 
-	if (guest_cbs && guest_cbs->state()) {
+	if (static_call(x86_guest_state)()) {
 		/* TODO: We don't support guest os callchain now */
 		return;
 	}
@@ -2865,11 +2887,10 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry_ctx *ent
 void
 perf_callchain_user(struct perf_callchain_entry_ctx *entry, struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
 	struct stack_frame frame;
 	const struct stack_frame __user *fp;
 
-	if (guest_cbs && guest_cbs->state()) {
+	if (static_call(x86_guest_state)()) {
 		/* TODO: We don't support guest os callchain now */
 		return;
 	}
@@ -2946,18 +2967,15 @@ static unsigned long code_segment_base(struct pt_regs *regs)
 
 unsigned long perf_instruction_pointer(struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-
-	if (guest_cbs && guest_cbs->state())
-		return guest_cbs->get_ip();
+	if (static_call(x86_guest_state)())
+		return static_call(x86_guest_get_ip)();
 
 	return regs->ip + code_segment_base(regs);
 }
 
 unsigned long perf_misc_flags(struct pt_regs *regs)
 {
-	struct perf_guest_info_callbacks *guest_cbs = perf_get_guest_cbs();
-	unsigned int guest_state = guest_cbs ? guest_cbs->state() : 0;
+	unsigned int guest_state = static_call(x86_guest_state)();
 	int misc = 0;
 
 	if (guest_state) {
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 524ad1f747bd..fb1bd7a0e1a6 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -2782,11 +2782,12 @@ static void intel_pmu_reset(void)
 	local_irq_restore(flags);
 }
 
+DECLARE_STATIC_CALL(x86_guest_handle_intel_pt_intr, *(perf_guest_cbs->handle_intel_pt_intr));
+
 static int handle_pmi_common(struct pt_regs *regs, u64 status)
 {
 	struct perf_sample_data data;
 	struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events);
-	struct perf_guest_info_callbacks *guest_cbs;
 	int bit;
 	int handled = 0;
 	u64 intel_ctrl = hybrid(cpuc->pmu, intel_ctrl);
@@ -2853,9 +2854,7 @@ static int handle_pmi_common(struct pt_regs *regs, u64 status)
 	 */
 	if (__test_and_clear_bit(GLOBAL_STATUS_TRACE_TOPAPMI_BIT, (unsigned long *)&status)) {
 		handled++;
-
-		guest_cbs = perf_get_guest_cbs();
-		if (likely(!guest_cbs || !guest_cbs->handle_intel_pt_intr()))
+		if (!static_call(x86_guest_handle_intel_pt_intr)())
 			intel_pt_interrupt();
 	}
 
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index a5d5893b80b0..3fa1014218f4 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1240,14 +1240,7 @@ extern void perf_event_bpf_event(struct bpf_prog *prog,
 
 #ifdef CONFIG_HAVE_GUEST_PERF_EVENTS
 extern struct perf_guest_info_callbacks *perf_guest_cbs;
-static inline struct perf_guest_info_callbacks *perf_get_guest_cbs(void)
-{
-	/* Reg/unreg perf_guest_cbs waits for readers via synchronize_rcu(). */
-	lockdep_assert_preemption_disabled();
-
-	/* Prevent reloading between a !NULL check and dereferences. */
-	return READ_ONCE(perf_guest_cbs);
-}
+extern void arch_perf_update_guest_cbs(struct perf_guest_info_callbacks *guest_cbs);
 extern void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
 extern void perf_unregister_guest_info_callbacks(void);
 #endif /* CONFIG_HAVE_GUEST_PERF_EVENTS */
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ec36e7aded89..fb0fd670ab23 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6491,6 +6491,7 @@ void perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *cbs)
 		return;
 
 	WRITE_ONCE(perf_guest_cbs, cbs);
+	arch_perf_update_guest_cbs(cbs);
 	synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
@@ -6498,6 +6499,7 @@ EXPORT_SYMBOL_GPL(perf_register_guest_info_callbacks);
 void perf_unregister_guest_info_callbacks(void)
 {
 	WRITE_ONCE(perf_guest_cbs, NULL);
+	arch_perf_update_guest_cbs(NULL);
 	synchronize_rcu();
 }
 EXPORT_SYMBOL_GPL(perf_unregister_guest_info_callbacks);
-- 
2.33.0.259.gc128427fd7-goog