Messages in this thread | | | Date | Thu, 3 Nov 2022 12:45:47 -0700 | Subject | Re: [PATCH bpf-next 2/3] bpf: Add bpf_perf_event_read_sample() helper | From | Yonghong Song <> |
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On 11/1/22 3:02 AM, Jiri Olsa wrote: > 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@kernel.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
Martin and I have discussed an idea to introduce a generic helper like bpf_get_kern_ctx(void *ctx) Given a context, the helper will return a PTR_TO_BTF_ID representing the corresponding kernel ctx. So in the above example, user could call
struct bpf_perf_event_data_kern *kctx = bpf_get_kern_ctx(ctx); ...
To implement bpf_get_kern_ctx helper, the verifier can find the type of the context and provide a hidden btf_id as the second parameter of the actual kernel helper function like bpf_get_kern_ctx(ctx) { return ctx; } /* based on ctx_btf_id, find kctx_btf_id and return it to verifier */
The bpf_get_kern_ctx helper can be inlined as well.
> >> + 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, >> +}; >> + >[...]
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