perf/x86/intel/pt: Add sampling support

Add AUX sampling support to the PT PMU: implement an NMI-safe callback that takes a snapshot of the buffer without touching the event states. This is done for PT events that don't use PMIs, that is, snapshot mode (RO mapping of the AUX area). Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: David Ahern <dsahern@gmail.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Cc: adrian.hunter@intel.com Cc: mathieu.poirier@linaro.org Link: https://lkml.kernel.org/r/20191025140835.53665-4-alexander.shishkin@linux.intel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>

Author: virtuoso

arch/x86/events/intel/pt.c

@@ -1208,6 +1208,13 @@ pt_buffer_setup_aux(struct perf_event *event, void **pages,
 if (!nr_pages)
 return NULL;
 
+/*
+ * Only support AUX sampling in snapshot mode, where we don't
+ * generate NMIs.
+ */
+if (event->attr.aux_sample_size && !snapshot)
+return NULL;
+
 if (cpu == -1)
 cpu = raw_smp_processor_id();
 node = cpu_to_node(cpu);
@@ -1506,6 +1513,52 @@ static void pt_event_stop(struct perf_event *event, int mode)
 }
 }
 
+static long pt_event_snapshot_aux(struct perf_event *event,
+ struct perf_output_handle *handle,
+ unsigned long size)
+{
+struct pt *pt = this_cpu_ptr(&pt_ctx);
+struct pt_buffer *buf = perf_get_aux(&pt->handle);
+unsigned long from = 0, to;
+long ret;
+
+if (WARN_ON_ONCE(!buf))
+return 0;
+
+/*
+ * Sampling is only allowed on snapshot events;
+ * see pt_buffer_setup_aux().
+ */
+if (WARN_ON_ONCE(!buf->snapshot))
+return 0;
+
+/*
+ * Here, handle_nmi tells us if the tracing is on
+ */
+if (READ_ONCE(pt->handle_nmi))
+pt_config_stop(event);
+
+pt_read_offset(buf);
+pt_update_head(pt);
+
+to = local_read(&buf->data_size);
+if (to < size)
+from = buf->nr_pages << PAGE_SHIFT;
+from += to - size;
+
+ret = perf_output_copy_aux(&pt->handle, handle, from, to);
+
+/*
+ * If the tracing was on when we turned up, restart it.
+ * Compiler barrier not needed as we couldn't have been
+ * preempted by anything that touches pt->handle_nmi.
+ */
+if (pt->handle_nmi)
+pt_config_start(event);
+
+return ret;
+}
+
 static void pt_event_del(struct perf_event *event, int mode)
 {
 pt_event_stop(event, PERF_EF_UPDATE);
@@ -1625,6 +1678,7 @@ static __init int pt_init(void)
 pt_pmu.pmu.del = pt_event_del;
 pt_pmu.pmu.start = pt_event_start;
 pt_pmu.pmu.stop = pt_event_stop;
+pt_pmu.pmu.snapshot_aux = pt_event_snapshot_aux;
 pt_pmu.pmu.read = pt_event_read;
 pt_pmu.pmu.setup_aux = pt_buffer_setup_aux;
 pt_pmu.pmu.free_aux = pt_buffer_free_aux;