Commit 98b5c2c6 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

perf, bpf: allow bpf programs attach to tracepoints 



introduce BPF_PROG_TYPE_TRACEPOINT program type and allow it to be attached
to the perf tracepoint handler, which will copy the arguments into
the per-cpu buffer and pass it to the bpf program as its first argument.
The layout of the fields can be discovered by doing
'cat /sys/kernel/debug/tracing/events/sched/sched_switch/format'
prior to the compilation of the program with exception that first 8 bytes
are reserved and not accessible to the program. This area is used to store
the pointer to 'struct pt_regs' which some of the bpf helpers will use:
+---------+
| 8 bytes | hidden 'struct pt_regs *' (inaccessible to bpf program)
+---------+
| N bytes | static tracepoint fields defined in tracepoint/format (bpf readonly)
+---------+
| dynamic | __dynamic_array bytes of tracepoint (inaccessible to bpf yet)
+---------+

Not that all of the fields are already dumped to user space via perf ring buffer
and broken application access it directly without consulting tracepoint/format.
Same rule applies here: static tracepoint fields should only be accessed
in a format defined in tracepoint/format. The order of fields and
field sizes are not an ABI.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1e1dcd93

include/trace/perf.h

+9 −1
Original line number Diff line number Diff line
@@ -34,6 +34,7 @@ perf_trace_##call(void *__data, proto) \ 
	struct trace_event_call *event_call = __data;			\

	struct trace_event_data_offsets_##call __maybe_unused __data_offsets;\

	struct trace_event_raw_##call *entry;				\

	struct bpf_prog *prog = event_call->prog;			\

	struct pt_regs *__regs;						\

	u64 __count = 1;						\

	struct task_struct *__task = NULL;				\
@@ -45,7 +46,7 @@ perf_trace_##call(void *__data, proto) \ 
	__data_size = trace_event_get_offsets_##call(&__data_offsets, args); \

									\

	head = this_cpu_ptr(event_call->perf_events);			\

	if (__builtin_constant_p(!__task) && !__task &&			\

	if (!prog && __builtin_constant_p(!__task) && !__task &&	\

				hlist_empty(head))			\

		return;							\

									\
@@ -63,6 +64,13 @@ perf_trace_##call(void *__data, proto) \ 
									\

	{ assign; }							\

									\

	if (prog) {							\

		*(struct pt_regs **)entry = __regs;			\

		if (!trace_call_bpf(prog, entry) || hlist_empty(head)) { \

			perf_swevent_put_recursion_context(rctx);	\

			return;						\

		}							\

	}								\

	perf_trace_buf_submit(entry, __entry_size, rctx,		\

			      event_call->event.type, __count, __regs,	\

			      head, __task);				\

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -92,6 +92,7 @@ enum bpf_prog_type { 
	BPF_PROG_TYPE_KPROBE,

	BPF_PROG_TYPE_SCHED_CLS,

	BPF_PROG_TYPE_SCHED_ACT,

	BPF_PROG_TYPE_TRACEPOINT,

};



#define BPF_PSEUDO_MAP_FD	1

kernel/events/core.c

+9 −4
Original line number Diff line number Diff line
@@ -6725,12 +6725,13 @@ int perf_swevent_get_recursion_context(void) 
}

EXPORT_SYMBOL_GPL(perf_swevent_get_recursion_context);



inline void perf_swevent_put_recursion_context(int rctx)

void perf_swevent_put_recursion_context(int rctx)

{

	struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);



	put_recursion_context(swhash->recursion, rctx);

}

EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);



void ___perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)

{
@@ -7106,6 +7107,7 @@ static void perf_event_free_filter(struct perf_event *event) 


static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)

{

	bool is_kprobe, is_tracepoint;

	struct bpf_prog *prog;



	if (event->attr.type != PERF_TYPE_TRACEPOINT)
@@ -7114,15 +7116,18 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd) 
	if (event->tp_event->prog)

		return -EEXIST;



	if (!(event->tp_event->flags & TRACE_EVENT_FL_UKPROBE))

		/* bpf programs can only be attached to u/kprobes */

	is_kprobe = event->tp_event->flags & TRACE_EVENT_FL_UKPROBE;

	is_tracepoint = event->tp_event->flags & TRACE_EVENT_FL_TRACEPOINT;

	if (!is_kprobe && !is_tracepoint)

		/* bpf programs can only be attached to u/kprobe or tracepoint */

		return -EINVAL;



	prog = bpf_prog_get(prog_fd);

	if (IS_ERR(prog))

		return PTR_ERR(prog);



	if (prog->type != BPF_PROG_TYPE_KPROBE) {

	if ((is_kprobe && prog->type != BPF_PROG_TYPE_KPROBE) ||

	    (is_tracepoint && prog->type != BPF_PROG_TYPE_TRACEPOINT)) {

		/* valid fd, but invalid bpf program type */

		bpf_prog_put(prog);

		return -EINVAL;

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