Re: [PATCH bpf-next 1/5] perf/core: Add PERF_FORMAT_LOST read_format

+	PERF_FORMAT_MAX = 1U << 5,		/* non-ABI */
 };
 
 #define PERF_ATTR_SIZE_VER0	64	/* sizeof first published struct */

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0463c1151bae..ee08d3ed6299 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c

@@ -1715,6 +1715,9 @@ static void __perf_event_read_size(struct perf_event *event, int nr_siblings)
 	if (event->attr.read_format & PERF_FORMAT_ID)
 		entry += sizeof(u64);
 
+	if (event->attr.read_format & PERF_FORMAT_LOST)
+		entry += sizeof(u64);
+
 	if (event->attr.read_format & PERF_FORMAT_GROUP) {
 		nr += nr_siblings;
 		size += sizeof(u64);

@@ -4734,6 +4737,24 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 }
 EXPORT_SYMBOL_GPL(perf_event_read_value);
 
+static struct pmu perf_kprobe;
+static u64 perf_event_lost(struct perf_event *event)
+{
+	struct ring_buffer *rb;
+	u64 lost = 0;
+
+	rcu_read_lock();
+	rb = rcu_dereference(event->rb);
+	if (likely(!!rb))
+		lost += local_read(&rb->lost);
+	rcu_read_unlock();
+
+	if (event->attr.type == perf_kprobe.type)
+		lost += perf_kprobe_missed(event);