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Date: Tue, 23 Aug 2022 22:19:19 +0000
From: Song Liu <songliubraving@...com>
To: Namhyung Kim <namhyung@...nel.org>
CC: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Stanislav Fomichev <sdf@...gle.com>,
Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf: Add bpf_read_raw_record() helper
> On Aug 23, 2022, at 2:03 PM, Namhyung Kim <namhyung@...nel.org> wrote:
>
> The helper is for BPF programs attached to perf_event in order to read
> event-specific raw data. I followed the convention of the
> bpf_read_branch_records() helper so that it can tell the size of
> record using BPF_F_GET_RAW_RECORD flag.
>
> The use case is to filter perf event samples based on the HW provided
> data which have more detailed information about the sample.
>
> Note that it only reads the first fragment of the raw record. But it
> seems mostly ok since all the existing PMU raw data have only single
> fragment and the multi-fragment records are only for BPF output attached
> to sockets. So unless it's used with such an extreme case, it'd work
> for most of tracing use cases.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> I don't know how to test this. As the raw data is available on some
> hardware PMU only (e.g. AMD IBS). I tried a tracepoint event but it was
> rejected by the verifier. Actually it needs a bpf_perf_event_data
> context so that's not an option IIUC.
Can we add a software event that generates raw data for testing?
Thanks,
Song
>
> include/uapi/linux/bpf.h | 23 ++++++++++++++++++++++
> kernel/trace/bpf_trace.c | 41 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 64 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 934a2a8beb87..af7f70564819 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -5355,6 +5355,23 @@ union bpf_attr {
> * Return
> * Current *ktime*.
> *
> + * long bpf_read_raw_record(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 flags)
> + * Description
> + * For an eBPF program attached to a perf event, retrieve the
> + * raw record associated to *ctx* and store it in the buffer
> + * pointed by *buf* up to size *size* bytes.
> + * Return
> + * On success, number of bytes written to *buf*. On error, a
> + * negative value.
> + *
> + * The *flags* can be set to **BPF_F_GET_RAW_RECORD_SIZE** to
> + * instead return the number of bytes required to store the raw
> + * record. If this flag is set, *buf* may be NULL.
> + *
> + * **-EINVAL** if arguments invalid or **size** not a multiple
> + * of **sizeof**\ (u64\ ).
> + *
> + * **-ENOENT** if the event does not have raw records.
> */
> #define __BPF_FUNC_MAPPER(FN) \
> FN(unspec), \
> @@ -5566,6 +5583,7 @@ union bpf_attr {
> FN(tcp_raw_check_syncookie_ipv4), \
> FN(tcp_raw_check_syncookie_ipv6), \
> FN(ktime_get_tai_ns), \
> + FN(read_raw_record), \
> /* */
>
> /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> @@ -5749,6 +5767,11 @@ enum {
> BPF_F_EXCLUDE_INGRESS = (1ULL << 4),
> };
>
> +/* BPF_FUNC_read_raw_record flags. */
> +enum {
> + BPF_F_GET_RAW_RECORD_SIZE = (1ULL << 0),
> +};
> +
> #define __bpf_md_ptr(type, name) \
> union { \
> type name; \
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 68e5cdd24cef..db172b12e5f8 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -20,6 +20,7 @@
> #include <linux/fprobe.h>
> #include <linux/bsearch.h>
> #include <linux/sort.h>
> +#include <linux/perf_event.h>
>
> #include <net/bpf_sk_storage.h>
>
> @@ -1532,6 +1533,44 @@ static const struct bpf_func_proto bpf_read_branch_records_proto = {
> .arg4_type = ARG_ANYTHING,
> };
>
> +BPF_CALL_4(bpf_read_raw_record, struct bpf_perf_event_data_kern *, ctx,
> + void *, buf, u32, size, u64, flags)
> +{
> + struct perf_raw_record *raw = ctx->data->raw;
> + struct perf_raw_frag *frag;
> + u32 to_copy;
> +
> + if (unlikely(flags & ~BPF_F_GET_RAW_RECORD_SIZE))
> + return -EINVAL;
> +
> + if (unlikely(!raw))
> + return -ENOENT;
> +
> + if (flags & BPF_F_GET_RAW_RECORD_SIZE)
> + return raw->size;
> +
> + if (!buf || (size % sizeof(u32) != 0))
> + return -EINVAL;
> +
> + frag = &raw->frag;
> + WARN_ON_ONCE(!perf_raw_frag_last(frag));
> +
> + to_copy = min_t(u32, frag->size, size);
> + memcpy(buf, frag->data, to_copy);
> +
> + return to_copy;
> +}
> +
> +static const struct bpf_func_proto bpf_read_raw_record_proto = {
> + .func = bpf_read_raw_record,
> + .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)
> {
> @@ -1548,6 +1587,8 @@ 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_read_raw_record:
> + return &bpf_read_raw_record_proto;
> default:
> return bpf_tracing_func_proto(func_id, prog);
> }
> --
> 2.37.2.609.g9ff673ca1a-goog
>
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