diff mbox series

[v1,2/7] bpf: Add bpf_perf_event_aux_pause kfunc

Message ID 20241215193436.275278-3-leo.yan@arm.com (mailing list archive)
State New
Headers show
Series perf auxtrace: Support AUX pause with BPF backend | expand

Commit Message

Leo Yan Dec. 15, 2024, 7:34 p.m. UTC 
The bpf_perf_event_aux_pause kfunc will be used to control the Perf AUX
area to pause or resume.

An example use-case is attaching eBPF to Ftrace tracepoints.  When a
tracepoint is hit, the associated eBPF program will be executed.  The
eBPF program can invoke bpf_perf_event_aux_pause() to pause or resume
AUX trace.  This is useful for fine-grained tracing by combining
Perf and eBPF.

This commit implements the bpf_perf_event_aux_pause kfunc, and make it
pass the eBPF verifier.

Signed-off-by: Leo Yan <leo.yan@arm.com>
---
 include/uapi/linux/bpf.h | 21 ++++++++++++++++
 kernel/bpf/verifier.c    |  2 ++
 kernel/trace/bpf_trace.c | 52 ++++++++++++++++++++++++++++++++++++++++
 3 files changed, 75 insertions(+)

Comments

Yonghong Song Dec. 16, 2024, 5:21 p.m. UTC | #1 
On 12/15/24 11:34 AM, Leo Yan wrote:
> The bpf_perf_event_aux_pause kfunc will be used to control the Perf AUX
> area to pause or resume.
>
> An example use-case is attaching eBPF to Ftrace tracepoints.  When a
> tracepoint is hit, the associated eBPF program will be executed.  The
> eBPF program can invoke bpf_perf_event_aux_pause() to pause or resume
> AUX trace.  This is useful for fine-grained tracing by combining
> Perf and eBPF.
>
> This commit implements the bpf_perf_event_aux_pause kfunc, and make it
> pass the eBPF verifier.

The subject and commit message mentions to implement a kfunc,
but actually you implemented a uapi helper. Please implement a kfunc
instead (searching __bpf_kfunc in kernel/bpf directory).

>
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>   include/uapi/linux/bpf.h | 21 ++++++++++++++++
>   kernel/bpf/verifier.c    |  2 ++
>   kernel/trace/bpf_trace.c | 52 ++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 75 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 4162afc6b5d0..678278c91ce2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5795,6 +5795,26 @@ union bpf_attr {
>    *		0 on success.
>    *
>    *		**-ENOENT** if the bpf_local_storage cannot be found.
> + *
> + * long bpf_perf_event_aux_pause(struct bpf_map *map, u64 flags, u32 pause)
> + *	Description
> + *		Pause or resume an AUX area trace associated to the perf event.
> + *
> + *		The *flags* argument is specified as the key value for
> + *		retrieving event pointer from the passed *map*.
> + *
> + *		The *pause* argument controls AUX trace pause or resume.
> + *		Non-zero values (true) are to pause the AUX trace and the zero
> + *		value (false) is for re-enabling the AUX trace.
> + *	Return
> + *		0 on success.
> + *
> + *		**-ENOENT** if not found event in the events map.
> + *
> + *		**-E2BIG** if the event index passed in the *flags* parameter
> + *		is out-of-range of the map.
> + *
> + *		**-EINVAL** if the flags passed is an invalid value.
>    */
>   #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
>   	FN(unspec, 0, ##ctx)				\
> @@ -6009,6 +6029,7 @@ union bpf_attr {
>   	FN(user_ringbuf_drain, 209, ##ctx)		\
>   	FN(cgrp_storage_get, 210, ##ctx)		\
>   	FN(cgrp_storage_delete, 211, ##ctx)		\
> +	FN(perf_event_aux_pause, 212, ##ctx)		\
>   	/* */
>   
>   /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
>
[...]
diff mbox series

Patch

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4162afc6b5d0..678278c91ce2 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5795,6 +5795,26 @@  union bpf_attr {
  *		0 on success.
  *
  *		**-ENOENT** if the bpf_local_storage cannot be found.
+ *
+ * long bpf_perf_event_aux_pause(struct bpf_map *map, u64 flags, u32 pause)
+ *	Description
+ *		Pause or resume an AUX area trace associated to the perf event.
+ *
+ *		The *flags* argument is specified as the key value for
+ *		retrieving event pointer from the passed *map*.
+ *
+ *		The *pause* argument controls AUX trace pause or resume.
+ *		Non-zero values (true) are to pause the AUX trace and the zero
+ *		value (false) is for re-enabling the AUX trace.
+ *	Return
+ *		0 on success.
+ *
+ *		**-ENOENT** if not found event in the events map.
+ *
+ *		**-E2BIG** if the event index passed in the *flags* parameter
+ *		is out-of-range of the map.
+ *
+ *		**-EINVAL** if the flags passed is an invalid value.
  */
 #define ___BPF_FUNC_MAPPER(FN, ctx...)			\
 	FN(unspec, 0, ##ctx)				\
@@ -6009,6 +6029,7 @@  union bpf_attr {
 	FN(user_ringbuf_drain, 209, ##ctx)		\
 	FN(cgrp_storage_get, 210, ##ctx)		\
 	FN(cgrp_storage_delete, 211, ##ctx)		\
+	FN(perf_event_aux_pause, 212, ##ctx)		\
 	/* */
 
 /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 09f7fa635f67..1f3acd8a7de3 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -9315,6 +9315,7 @@  static int check_map_func_compatibility(struct bpf_verifier_env *env,
 		    func_id != BPF_FUNC_perf_event_output &&
 		    func_id != BPF_FUNC_skb_output &&
 		    func_id != BPF_FUNC_perf_event_read_value &&
+		    func_id != BPF_FUNC_perf_event_aux_pause &&
 		    func_id != BPF_FUNC_xdp_output)
 			goto error;
 		break;
@@ -9443,6 +9444,7 @@  static int check_map_func_compatibility(struct bpf_verifier_env *env,
 	case BPF_FUNC_perf_event_read:
 	case BPF_FUNC_perf_event_output:
 	case BPF_FUNC_perf_event_read_value:
+	case BPF_FUNC_perf_event_aux_pause:
 	case BPF_FUNC_skb_output:
 	case BPF_FUNC_xdp_output:
 		if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 949a3870946c..a3b857f6cab4 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -617,6 +617,56 @@  static const struct bpf_func_proto bpf_perf_event_read_value_proto = {
 	.arg4_type	= ARG_CONST_SIZE,
 };
 
+BPF_CALL_3(bpf_perf_event_aux_pause, struct bpf_map *, map, u64, flags,
+	   u32, pause)
+{
+	unsigned long irq_flags;
+	struct bpf_array *array = container_of(map, struct bpf_array, map);
+	unsigned int cpu = smp_processor_id();
+	u64 index = flags & BPF_F_INDEX_MASK;
+	struct bpf_event_entry *ee;
+	int ret = 0;
+
+	/*
+	 * Disabling interrupts avoids scheduling and race condition with
+	 * perf event enabling and disabling flow.
+	 */
+	local_irq_save(irq_flags);
+
+	if (unlikely(flags & ~(BPF_F_INDEX_MASK))) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	if (index == BPF_F_CURRENT_CPU)
+		index = cpu;
+	if (unlikely(index >= array->map.max_entries)) {
+		ret = -E2BIG;
+		goto out;
+	}
+
+	ee = READ_ONCE(array->ptrs[index]);
+	if (!ee) {
+		ret = -ENOENT;
+		goto out;
+	}
+
+	perf_event_aux_pause(ee->event, pause);
+
+out:
+	local_irq_restore(irq_flags);
+	return ret;
+}
+
+static const struct bpf_func_proto bpf_perf_event_aux_pause_proto = {
+	.func		= bpf_perf_event_aux_pause,
+	.gpl_only	= true,
+	.ret_type	= RET_INTEGER,
+	.arg1_type	= ARG_CONST_MAP_PTR,
+	.arg2_type	= ARG_ANYTHING,
+	.arg3_type	= ARG_ANYTHING,
+};
+
 static __always_inline u64
 __bpf_perf_event_output(struct pt_regs *regs, struct bpf_map *map,
 			u64 flags, struct perf_sample_data *sd)
@@ -1565,6 +1615,8 @@  bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_find_vma_proto;
 	case BPF_FUNC_trace_vprintk:
 		return bpf_get_trace_vprintk_proto();
+	case BPF_FUNC_perf_event_aux_pause:
+		return &bpf_perf_event_aux_pause_proto;
 	default:
 		return bpf_base_func_proto(func_id, prog);
 	}