[PATCH 4/4] mm/damon: Hide kernel pointer from tracepoint event

[SeongJae Park]

DAMON's virtual address spaces monitoring primitive uses 'struct pid *'
of the target process as its monitoring target id.  The kernel address
is exposed as-is to the user space via the DAMON tracepoint,
'damon_aggregated'.  Though primarily only privileged users are allowed
to access that, it would be better to avoid unnecessarily exposing
kernel pointers so.  Because the trace result is only required to be
able to distinguish each target, we aren't need to use the pointer
as-is.  This commit makes the tracepoint to use the index of the target
in the context's targets list as its id in the tracepoint, to hide the
kernel space address.

Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
 include/trace/events/damon.h | 8 ++++----
 mm/damon/core.c              | 4 +++-
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 99ffa601e351..c79f1d4c39af 100644
--- a/include/trace/events/damon.h
+++ b/include/trace/events/damon.h
@@ -11,10 +11,10 @@
 
 TRACE_EVENT(damon_aggregated,
 
-	TP_PROTO(struct damon_target *t, struct damon_region *r,
-		unsigned int nr_regions),
+	TP_PROTO(struct damon_target *t, unsigned int target_id,
+		struct damon_region *r, unsigned int nr_regions),
 
-	TP_ARGS(t, r, nr_regions),
+	TP_ARGS(t, target_id, r, nr_regions),
 
 	TP_STRUCT__entry(
 		__field(unsigned long, target_id)
@@ -26,7 +26,7 @@ TRACE_EVENT(damon_aggregated,
 	),
 
 	TP_fast_assign(
-		__entry->target_id = t->id;
+		__entry->target_id = target_id;
 		__entry->nr_regions = nr_regions;
 		__entry->start = r->ar.start;
 		__entry->end = r->ar.end;
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6482d510dcbe..1dd153c31c9e 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -514,15 +514,17 @@ static bool kdamond_aggregate_interval_passed(struct damon_ctx *ctx)
 static void kdamond_reset_aggregated(struct damon_ctx *c)
 {
 	struct damon_target *t;
+	unsigned int ti = 0;	/* target's index */
 
 	damon_for_each_target(t, c) {
 		struct damon_region *r;
 
 		damon_for_each_region(r, t) {
-			trace_damon_aggregated(t, r, damon_nr_regions(t));
+			trace_damon_aggregated(t, ti, r, damon_nr_regions(t));
 			r->last_nr_accesses = r->nr_accesses;
 			r->nr_accesses = 0;
 		}
+		ti++;
 	}
 }
 
-- 
2.17.1