tracing: Allow BPF programs to call bpf_ktime_get_ns()

bpf_ktime_get_ns() is used by programs to compute time delta
between events or as a timestamp

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1427312966-8434-5-git-send-email-ast@plumgrid.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 15 insertions, 0 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index b2948feeb70b..238c6883877b 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -165,6 +165,7 @@ enum bpf_func_id {
         BPF_FUNC_map_update_elem, /* int map_update_elem(&map, &key, &value, flags) */
         BPF_FUNC_map_delete_elem, /* int map_delete_elem(&map, &key) */
         BPF_FUNC_probe_read,      /* int bpf_probe_read(void *dst, int size, void *src) */
+        BPF_FUNC_ktime_get_ns,    /* u64 bpf_ktime_get_ns(void) */
         __BPF_FUNC_MAX_ID,
 };
 
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index f1e87da91da3..8f5787294971 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -78,6 +78,18 @@ static const struct bpf_func_proto bpf_probe_read_proto = {
         .arg3_type      = ARG_ANYTHING,
 };
 
+static u64 bpf_ktime_get_ns(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5)
+{
+        /* NMI safe access to clock monotonic */
+        return ktime_get_mono_fast_ns();
+}
+
+static const struct bpf_func_proto bpf_ktime_get_ns_proto = {
+        .func           = bpf_ktime_get_ns,
+        .gpl_only       = true,
+        .ret_type       = RET_INTEGER,
+};
+
 static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func_id)
 {
         switch (func_id) {
@@ -89,6 +101,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
                 return &bpf_map_delete_elem_proto;
         case BPF_FUNC_probe_read:
                 return &bpf_probe_read_proto;
+        case BPF_FUNC_ktime_get_ns:
+                return &bpf_ktime_get_ns_proto;
         default:
                 return NULL;
         }