mm/damon: hide kernel pointer from tracepoint event

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 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.

Link: https://lkml.kernel.org/r/20211229131016.23641-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/trace/events/damon.h b/include/trace/events/damon.h
index 99ffa601e35119877d93c6ddd1b58c929ede3322..c79f1d4c39afe754a18d3c646a0bd262e531eb83 100644 (file)
--- 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 6482d510dcbe315ed1479280cfd8655db2327217..1dd153c31c9e2b8e5fd6bc7d608f830e768f9c1e 100644 (file)
--- 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++;
        }
 }