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@xxxxxxxxxx>
---
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,
+};
+
[...]
