[PATCH v5 1/4] perf/bpf: Call bpf handler directly, not through overflow machinery

[PATCH v5 1/4] perf/bpf: Call bpf handler directly, not through overflow machinery

[Kyle Huey]

To ultimately allow bpf programs attached to perf events to completely
suppress all of the effects of a perf event overflow (rather than just the
sample output, as they do today), call bpf_overflow_handler() from
__perf_event_overflow() directly rather than modifying struct perf_event's
overflow_handler. Return the bpf program's return value from
bpf_overflow_handler() so that __perf_event_overflow() knows how to
proceed. Remove the now unnecessary orig_overflow_handler from struct
perf_event.

This patch is solely a refactoring and results in no behavior change.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Suggested-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/perf_event.h |  6 +-----
 kernel/events/core.c       | 28 +++++++++++++++-------------
 2 files changed, 16 insertions(+), 18 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d2a15c0c6f8a..c7f54fd74d89 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -810,7 +810,6 @@ struct perf_event {
 	perf_overflow_handler_t		overflow_handler;
 	void				*overflow_handler_context;
 #ifdef CONFIG_BPF_SYSCALL
-	perf_overflow_handler_t		orig_overflow_handler;
 	struct bpf_prog			*prog;
 	u64				bpf_cookie;
 #endif
@@ -1357,10 +1356,7 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
 #ifdef CONFIG_BPF_SYSCALL
 static inline bool uses_default_overflow_handler(struct perf_event *event)
 {
-	if (likely(is_default_overflow_handler(event)))
-		return true;
-
-	return __is_default_overflow_handler(event->orig_overflow_handler);
+	return is_default_overflow_handler(event);
 }
 #else
 #define uses_default_overflow_handler(event) \
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f0f0f71213a1..24a718e7eb98 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9548,6 +9548,12 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r
 	return true;
 }
 
+#ifdef CONFIG_BPF_SYSCALL
+static int bpf_overflow_handler(struct perf_event *event,
+				struct perf_sample_data *data,
+				struct pt_regs *regs);
+#endif
+
 /*
  * Generic event overflow handling, sampling.
  */
@@ -9617,7 +9623,10 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending_irq);
 	}
 
-	READ_ONCE(event->overflow_handler)(event, data, regs);
+#ifdef CONFIG_BPF_SYSCALL
+	if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
+#endif
+		READ_ONCE(event->overflow_handler)(event, data, regs);
 
 	if (*perf_event_fasync(event) && event->pending_kill) {
 		event->pending_wakeup = 1;
@@ -10427,9 +10436,9 @@ static void perf_event_free_filter(struct perf_event *event)
 }
 
 #ifdef CONFIG_BPF_SYSCALL
-static void bpf_overflow_handler(struct perf_event *event,
-				 struct perf_sample_data *data,
-				 struct pt_regs *regs)
+static int bpf_overflow_handler(struct perf_event *event,
+				struct perf_sample_data *data,
+				struct pt_regs *regs)
 {
 	struct bpf_perf_event_data_kern ctx = {
 		.data = data,
@@ -10450,10 +10459,8 @@ static void bpf_overflow_handler(struct perf_event *event,
 	rcu_read_unlock();
 out:
 	__this_cpu_dec(bpf_prog_active);
-	if (!ret)
-		return;
 
-	event->orig_overflow_handler(event, data, regs);
+	return ret;
 }
 
 static int perf_event_set_bpf_handler(struct perf_event *event,
@@ -10489,8 +10496,6 @@ static int perf_event_set_bpf_handler(struct perf_event *event,
 
 	event->prog = prog;
 	event->bpf_cookie = bpf_cookie;
-	event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
-	WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);
 	return 0;
 }
 
@@ -10501,7 +10506,6 @@ static void perf_event_free_bpf_handler(struct perf_event *event)
 	if (!prog)
 		return;
 
-	WRITE_ONCE(event->overflow_handler, event->orig_overflow_handler);
 	event->prog = NULL;
 	bpf_prog_put(prog);
 }
@@ -11975,13 +11979,11 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 		overflow_handler = parent_event->overflow_handler;
 		context = parent_event->overflow_handler_context;
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING)
-		if (overflow_handler == bpf_overflow_handler) {
+		if (parent_event->prog) {
 			struct bpf_prog *prog = parent_event->prog;
 
 			bpf_prog_inc(prog);
 			event->prog = prog;
-			event->orig_overflow_handler =
-				parent_event->orig_overflow_handler;
 		}
 #endif
 	}
-- 
2.34.1

[PATCH v5 2/4] perf/bpf: Remove unneeded uses_default_overflow_handler.

[Kyle Huey]

Now that struct perf_event's orig_overflow_handler is gone, there's no need
for the functions and macros to support looking past overflow_handler to
orig_overflow_handler.

This patch is solely a refactoring and results in no behavior change.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
---
 arch/arm/kernel/hw_breakpoint.c   |  8 ++++----
 arch/arm64/kernel/hw_breakpoint.c |  4 ++--
 include/linux/perf_event.h        | 16 ++--------------
 3 files changed, 8 insertions(+), 20 deletions(-)

diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index dc0fb7a81371..054e9199f30d 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -626,7 +626,7 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
 	hw->address &= ~alignment_mask;
 	hw->ctrl.len <<= offset;
 
-	if (uses_default_overflow_handler(bp)) {
+	if (is_default_overflow_handler(bp)) {
 		/*
 		 * Mismatch breakpoints are required for single-stepping
 		 * breakpoints.
@@ -798,7 +798,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 		 * Otherwise, insert a temporary mismatch breakpoint so that
 		 * we can single-step over the watchpoint trigger.
 		 */
-		if (!uses_default_overflow_handler(wp))
+		if (!is_default_overflow_handler(wp))
 			continue;
 step:
 		enable_single_step(wp, instruction_pointer(regs));
@@ -811,7 +811,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
 		info->trigger = addr;
 		pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
 		perf_bp_event(wp, regs);
-		if (uses_default_overflow_handler(wp))
+		if (is_default_overflow_handler(wp))
 			enable_single_step(wp, instruction_pointer(regs));
 	}
 
@@ -886,7 +886,7 @@ static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs)
 			info->trigger = addr;
 			pr_debug("breakpoint fired: address = 0x%x\n", addr);
 			perf_bp_event(bp, regs);
-			if (uses_default_overflow_handler(bp))
+			if (is_default_overflow_handler(bp))
 				enable_single_step(bp, addr);
 			goto unlock;
 		}
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index 35225632d70a..db2a1861bb97 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -654,7 +654,7 @@ static int breakpoint_handler(unsigned long unused, unsigned long esr,
 		perf_bp_event(bp, regs);
 
 		/* Do we need to handle the stepping? */
-		if (uses_default_overflow_handler(bp))
+		if (is_default_overflow_handler(bp))
 			step = 1;
 unlock:
 		rcu_read_unlock();
@@ -733,7 +733,7 @@ static u64 get_distance_from_watchpoint(unsigned long addr, u64 val,
 static int watchpoint_report(struct perf_event *wp, unsigned long addr,
 			     struct pt_regs *regs)
 {
-	int step = uses_default_overflow_handler(wp);
+	int step = is_default_overflow_handler(wp);
 	struct arch_hw_breakpoint *info = counter_arch_bp(wp);
 
 	info->trigger = addr;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c7f54fd74d89..c8bd5bb6610c 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1341,8 +1341,9 @@ extern int perf_event_output(struct perf_event *event,
 			     struct pt_regs *regs);
 
 static inline bool
-__is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
+is_default_overflow_handler(struct perf_event *event)
 {
+	perf_overflow_handler_t overflow_handler = event->overflow_handler;
 	if (likely(overflow_handler == perf_event_output_forward))
 		return true;
 	if (unlikely(overflow_handler == perf_event_output_backward))
@@ -1350,19 +1351,6 @@ __is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
 	return false;
 }
 
-#define is_default_overflow_handler(event) \
-	__is_default_overflow_handler((event)->overflow_handler)
-
-#ifdef CONFIG_BPF_SYSCALL
-static inline bool uses_default_overflow_handler(struct perf_event *event)
-{
-	return is_default_overflow_handler(event);
-}
-#else
-#define uses_default_overflow_handler(event) \
-	is_default_overflow_handler(event)
-#endif
-
 extern void
 perf_event_header__init_id(struct perf_event_header *header,
 			   struct perf_sample_data *data,
-- 
2.34.1

[PATCH v5 3/4] perf/bpf: Allow a bpf program to suppress all sample side effects

[Kyle Huey]

Returning zero from a bpf program attached to a perf event already
suppresses any data output. Return early from __perf_event_overflow() in
this case so it will also suppress event_limit accounting, SIGTRAP
generation, and F_ASYNC signalling.

Signed-off-by: Kyle Huey <khuey@kylehuey.com>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
---
 kernel/events/core.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 24a718e7eb98..a329bec42c4d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9574,6 +9574,11 @@ static int __perf_event_overflow(struct perf_event *event,
 
 	ret = __perf_event_account_interrupt(event, throttle);
 
+#ifdef CONFIG_BPF_SYSCALL
+	if (event->prog && !bpf_overflow_handler(event, data, regs))
+		return ret;
+#endif
+
 	/*
 	 * XXX event_limit might not quite work as expected on inherited
 	 * events
@@ -9623,10 +9628,7 @@ static int __perf_event_overflow(struct perf_event *event,
 		irq_work_queue(&event->pending_irq);
 	}
 
-#ifdef CONFIG_BPF_SYSCALL
-	if (!(event->prog && !bpf_overflow_handler(event, data, regs)))
-#endif
-		READ_ONCE(event->overflow_handler)(event, data, regs);
+	READ_ONCE(event->overflow_handler)(event, data, regs);
 
 	if (*perf_event_fasync(event) && event->pending_kill) {
 		event->pending_wakeup = 1;
-- 
2.34.1