Subject: Re: [PATCH net-next 2/3] bpf: introduce bpf_perf_event_output() helper

From: He Kuang <[email-masked]>
Date: Wed, 21 Oct 2015 18:01:05 +0800

hi, Alexei

I've tested the sample in next patch and it works well. I think more work on
the perf side needs to be done for parsing PERF_COUNT_SW_BPF_OUTPUT event type,
are you working on that?

Thank you.

On 2015/10/21 11:02, Alexei Starovoitov wrote:
> This helper is used to send raw data from eBPF program into
> special PERF_TYPE_SOFTWARE/PERF_COUNT_SW_BPF_OUTPUT perf_event.
> User space needs to perf_event_open() it (either for one or all cpus) and
> store FD into perf_event_array (similar to bpf_perf_event_read() helper)
> before eBPF program can send data into it.
>
> Today the programs triggered by kprobe collect the data and either store
> it into the maps or print it via bpf_trace_printk() where latter is the debug
> facility and not suitable to stream the data. This new helper replaces
> such bpf_trace_printk() usage and allows programs to have dedicated
> channel into user space for post-processing of the raw data collected.
>
> Signed-off-by: Alexei Starovoitov <[email-masked]>
> ---
>   include/uapi/linux/bpf.h        |   11 ++++++++++
>   include/uapi/linux/perf_event.h |    1 +
>   kernel/bpf/arraymap.c           |    2 ++
>   kernel/bpf/verifier.c           |    3 ++-
>   kernel/trace/bpf_trace.c        |   46 +++++++++++++++++++++++++++++++++++++++
>   5 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 564f1f091991..2e032426cfb7 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -287,6 +287,17 @@ enum bpf_func_id {
>   	 * Return: realm if != 0
>   	 */
>   	BPF_FUNC_get_route_realm,
> +
> +	/**
> +	 * bpf_perf_event_output(ctx, map, index, data, size) - output perf raw sample
> +	 * @ctx: struct pt_regs*
> +	 * @map: pointer to perf_event_array map
> +	 * @index: index of event in the map
> +	 * @data: data on stack to be output as raw data
> +	 * @size: size of data
> +	 * Return: 0 on success
> +	 */
> +	BPF_FUNC_perf_event_output,
>   	__BPF_FUNC_MAX_ID,
>   };
>
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 2881145cda86..d3c417615361 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -110,6 +110,7 @@ enum perf_sw_ids {
>   	PERF_COUNT_SW_ALIGNMENT_FAULTS		= 7,
>   	PERF_COUNT_SW_EMULATION_FAULTS		= 8,
>   	PERF_COUNT_SW_DUMMY			= 9,
> +	PERF_COUNT_SW_BPF_OUTPUT		= 10,
>
>   	PERF_COUNT_SW_MAX,			/* non-ABI */
>   };
> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> index f2d9e698c753..e3cfe46b074f 100644
> --- a/kernel/bpf/arraymap.c
> +++ b/kernel/bpf/arraymap.c
> @@ -295,6 +295,8 @@ static void *perf_event_fd_array_get_ptr(struct bpf_map *map, int fd)
>   		return (void *)attr;
>
>   	if (attr->type != PERF_TYPE_RAW &&
> +	    !(attr->type == PERF_TYPE_SOFTWARE &&
> +	      attr->config == PERF_COUNT_SW_BPF_OUTPUT) &&
>   	    attr->type != PERF_TYPE_HARDWARE) {
>   		perf_event_release_kernel(event);
>   		return ERR_PTR(-EINVAL);
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 1d6b97be79e1..b56cf51f8d42 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -245,6 +245,7 @@ static const struct {
>   } func_limit[] = {
>   	{BPF_MAP_TYPE_PROG_ARRAY, BPF_FUNC_tail_call},
>   	{BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_read},
> +	{BPF_MAP_TYPE_PERF_EVENT_ARRAY, BPF_FUNC_perf_event_output},
>   };
>
>   static void print_verifier_state(struct verifier_env *env)
> @@ -910,7 +911,7 @@ static int check_map_func_compatibility(struct bpf_map *map, int func_id)
>   		 * don't allow any other map type to be passed into
>   		 * the special func;
>   		 */
> -		if (bool_map != bool_func)
> +		if (bool_func && bool_map != bool_func)
>   			return -EINVAL;
>   	}
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 0fe96c7c8803..47febbe7998e 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -215,6 +215,50 @@ const struct bpf_func_proto bpf_perf_event_read_proto = {
>   	.arg2_type	= ARG_ANYTHING,
>   };
>
> +static u64 bpf_perf_event_output(u64 r1, u64 r2, u64 index, u64 r4, u64 size)
> +{
> +	struct pt_regs *regs = (struct pt_regs *) (long) r1;
> +	struct bpf_map *map = (struct bpf_map *) (long) r2;
> +	struct bpf_array *array = container_of(map, struct bpf_array, map);
> +	void *data = (void *) (long) r4;
> +	struct perf_sample_data sample_data;
> +	struct perf_event *event;
> +	struct perf_raw_record raw = {
> +		.size = size,
> +		.data = data,
> +	};
> +
> +	if (unlikely(index >= array->map.max_entries))
> +		return -E2BIG;
> +
> +	event = (struct perf_event *)array->ptrs[index];
> +	if (unlikely(!event))
> +		return -ENOENT;
> +
> +	if (unlikely(event->attr.type != PERF_TYPE_SOFTWARE ||
> +		     event->attr.config != PERF_COUNT_SW_BPF_OUTPUT))
> +		return -EINVAL;
> +
> +	if (unlikely(event->oncpu != smp_processor_id()))
> +		return -EOPNOTSUPP;
> +
> +	perf_sample_data_init(&sample_data, 0, 0);
> +	sample_data.raw = &raw;
> +	perf_event_output(event, &sample_data, regs);
> +	return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_perf_event_output_proto = {
> +	.func		= bpf_perf_event_output,
> +	.gpl_only	= false,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_CTX,
> +	.arg2_type	= ARG_CONST_MAP_PTR,
> +	.arg3_type	= ARG_ANYTHING,
> +	.arg4_type	= ARG_PTR_TO_STACK,
> +	.arg5_type	= ARG_CONST_STACK_SIZE,
> +};
> +
>   static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
>   {
>   	switch (func_id) {
> @@ -242,6 +286,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
>   		return &bpf_get_smp_processor_id_proto;
>   	case BPF_FUNC_perf_event_read:
>   		return &bpf_perf_event_read_proto;
> +	case BPF_FUNC_perf_event_output:
> +		return &bpf_perf_event_output_proto;
>   	default:
>   		return NULL;
>   	}
>