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Date: Tue, 1 Nov 2022 11:02:54 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Song Liu <songliubraving@...com>,
Peter Zijlstra <peterz@...radead.org>,
Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
Stanislav Fomichev <sdf@...gle.com>,
LKML <linux-kernel@...r.kernel.org>, bpf@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [PATCH bpf-next 2/3] bpf: Add bpf_perf_event_read_sample() helper
On Mon, Oct 31, 2022 at 10:23:39PM -0700, Namhyung Kim wrote:
> The bpf_perf_event_read_sample() helper is to get the specified sample
> data (by using PERF_SAMPLE_* flag in the argument) from BPF to make a
> decision for filtering on samples. Currently PERF_SAMPLE_IP and
> PERF_SAMPLE_DATA flags are supported only.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> include/uapi/linux/bpf.h | 23 ++++++++++++++++
> kernel/trace/bpf_trace.c | 49 ++++++++++++++++++++++++++++++++++
> tools/include/uapi/linux/bpf.h | 23 ++++++++++++++++
> 3 files changed, 95 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 94659f6b3395..cba501de9373 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5481,6 +5481,28 @@ union bpf_attr {
> * 0 on success.
> *
> * **-ENOENT** if the bpf_local_storage cannot be found.
> + *
> + * long bpf_perf_event_read_sample(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 sample_flags)
> + * Description
> + * For an eBPF program attached to a perf event, retrieve the
> + * sample data associated to *ctx* and store it in the buffer
> + * pointed by *buf* up to size *size* bytes.
> + *
> + * The *sample_flags* should contain a single value in the
> + * **enum perf_event_sample_format**.
> + * Return
> + * On success, number of bytes written to *buf*. On error, a
> + * negative value.
> + *
> + * The *buf* can be set to **NULL** to return the number of bytes
> + * required to store the requested sample data.
> + *
> + * **-EINVAL** if *sample_flags* is not a PERF_SAMPLE_* flag.
> + *
> + * **-ENOENT** if the associated perf event doesn't have the data.
> + *
> + * **-ENOSYS** if system doesn't support the sample data to be
> + * retrieved.
> */
> #define ___BPF_FUNC_MAPPER(FN, ctx...) \
> FN(unspec, 0, ##ctx) \
> @@ -5695,6 +5717,7 @@ union bpf_attr {
> FN(user_ringbuf_drain, 209, ##ctx) \
> FN(cgrp_storage_get, 210, ##ctx) \
> FN(cgrp_storage_delete, 211, ##ctx) \
> + FN(perf_event_read_sample, 212, ##ctx) \
> /* */
>
> /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index ce0228c72a93..befd937afa3c 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -28,6 +28,7 @@
>
> #include <uapi/linux/bpf.h>
> #include <uapi/linux/btf.h>
> +#include <uapi/linux/perf_event.h>
>
> #include <asm/tlb.h>
>
> @@ -1743,6 +1744,52 @@ static const struct bpf_func_proto bpf_read_branch_records_proto = {
> .arg4_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_4(bpf_perf_event_read_sample, struct bpf_perf_event_data_kern *, ctx,
> + void *, buf, u32, size, u64, flags)
> +{
I wonder we could add perf_btf (like we have tp_btf) program type that
could access ctx->data directly without helpers
> + struct perf_sample_data *sd = ctx->data;
> + void *data;
> + u32 to_copy = sizeof(u64);
> +
> + /* only allow a single sample flag */
> + if (!is_power_of_2(flags))
> + return -EINVAL;
> +
> + /* support reading only already populated info */
> + if (flags & ~sd->sample_flags)
> + return -ENOENT;
> +
> + switch (flags) {
> + case PERF_SAMPLE_IP:
> + data = &sd->ip;
> + break;
> + case PERF_SAMPLE_ADDR:
> + data = &sd->addr;
> + break;
AFAICS from pe_prog_convert_ctx_access you should be able to read addr
directly from context right? same as sample_period.. so I think if this
will be generic way to read sample data, should we add sample_period
as well?
> + default:
> + return -ENOSYS;
> + }
> +
> + if (!buf)
> + return to_copy;
> +
> + if (size < to_copy)
> + to_copy = size;
should we fail in here instead? is there any point in returning
not complete data?
jirka
> +
> + memcpy(buf, data, to_copy);
> + return to_copy;
> +}
> +
> +static const struct bpf_func_proto bpf_perf_event_read_sample_proto = {
> + .func = bpf_perf_event_read_sample,
> + .gpl_only = true,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_PTR_TO_MEM_OR_NULL,
> + .arg3_type = ARG_CONST_SIZE_OR_ZERO,
> + .arg4_type = ARG_ANYTHING,
> +};
> +
> static const struct bpf_func_proto *
> pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> {
> @@ -1759,6 +1806,8 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> return &bpf_read_branch_records_proto;
> case BPF_FUNC_get_attach_cookie:
> return &bpf_get_attach_cookie_proto_pe;
> + case BPF_FUNC_perf_event_read_sample:
> + return &bpf_perf_event_read_sample_proto;
> default:
> return bpf_tracing_func_proto(func_id, prog);
> }
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 94659f6b3395..cba501de9373 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -5481,6 +5481,28 @@ union bpf_attr {
> * 0 on success.
> *
> * **-ENOENT** if the bpf_local_storage cannot be found.
> + *
> + * long bpf_perf_event_read_sample(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 sample_flags)
> + * Description
> + * For an eBPF program attached to a perf event, retrieve the
> + * sample data associated to *ctx* and store it in the buffer
> + * pointed by *buf* up to size *size* bytes.
> + *
> + * The *sample_flags* should contain a single value in the
> + * **enum perf_event_sample_format**.
> + * Return
> + * On success, number of bytes written to *buf*. On error, a
> + * negative value.
> + *
> + * The *buf* can be set to **NULL** to return the number of bytes
> + * required to store the requested sample data.
> + *
> + * **-EINVAL** if *sample_flags* is not a PERF_SAMPLE_* flag.
> + *
> + * **-ENOENT** if the associated perf event doesn't have the data.
> + *
> + * **-ENOSYS** if system doesn't support the sample data to be
> + * retrieved.
> */
> #define ___BPF_FUNC_MAPPER(FN, ctx...) \
> FN(unspec, 0, ##ctx) \
> @@ -5695,6 +5717,7 @@ union bpf_attr {
> FN(user_ringbuf_drain, 209, ##ctx) \
> FN(cgrp_storage_get, 210, ##ctx) \
> FN(cgrp_storage_delete, 211, ##ctx) \
> + FN(perf_event_read_sample, 212, ##ctx) \
> /* */
>
> /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't
> --
> 2.38.1.273.g43a17bfeac-goog
>
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