perf/arm-cmn: Move group validation data off-stack

With the value of CMN_MAX_DTMS increasing significantly, our validation
data structure is set to get quite big. Technically we could pack it at
least twice as densely, since we only need around 19 bits of information
per DTM, but that makes the code even more mind-bogglingly impenetrable,
and even half of "quite big" may still be uncomfortably large for a
stack frame (~1KB). Just move it to an off-stack allocation instead.

Signed-off-by: Robin Murphy <[email protected]>
Link: https://lore.kernel.org/r/0cabff2e5839ddc0979e757c55515966f65359e4.1638530442.git.robin.murphy@arm.com
Signed-off-by: Will Deacon <[email protected]>

Author: rmurphy-arm

drivers/perf/arm-cmn.c

@@ -876,8 +876,8 @@ static int arm_cmn_validate_group(struct perf_event *event)
 	struct arm_cmn_node *dn;
 	struct perf_event *sibling, *leader = event->group_leader;
 	enum cmn_node_type type;
-	struct arm_cmn_val val;
-	int i;
+	struct arm_cmn_val *val;
+	int i, ret = -EINVAL;
 	u8 occupid;
 
 	if (leader == event)
@@ -886,18 +886,22 @@ static int arm_cmn_validate_group(struct perf_event *event)
 	if (event->pmu != leader->pmu && !is_software_event(leader))
 		return -EINVAL;
 
-	memset(&val, 0, sizeof(val));
+	val = kzalloc(sizeof(*val), GFP_KERNEL);
+	if (!val)
+		return -ENOMEM;
 
-	arm_cmn_val_add_event(&val, leader);
+	arm_cmn_val_add_event(val, leader);
 	for_each_sibling_event(sibling, leader)
-		arm_cmn_val_add_event(&val, sibling);
+		arm_cmn_val_add_event(val, sibling);
 
 	type = CMN_EVENT_TYPE(event);
-	if (type == CMN_TYPE_DTC)
-		return val.cycles ? -EINVAL : 0;
+	if (type == CMN_TYPE_DTC) {
+		ret = val->cycles ? -EINVAL : 0;
+		goto done;
+	}
 
-	if (val.dtc_count == CMN_DT_NUM_COUNTERS)
-		return -EINVAL;
+	if (val->dtc_count == CMN_DT_NUM_COUNTERS)
+		goto done;
 
 	if (arm_cmn_is_occup_event(type, CMN_EVENT_EVENTID(event)))
 		occupid = CMN_EVENT_OCCUPID(event) + 1;
@@ -907,25 +911,28 @@ static int arm_cmn_validate_group(struct perf_event *event)
 	for_each_hw_dn(hw, dn, i) {
 		int wp_idx, wp_cmb, dtm = dn->dtm;
 
-		if (val.dtm_count[dtm] == CMN_DTM_NUM_COUNTERS)
-			return -EINVAL;
+		if (val->dtm_count[dtm] == CMN_DTM_NUM_COUNTERS)
+			goto done;
 
-		if (occupid && val.occupid[dtm] && occupid != val.occupid[dtm])
-			return -EINVAL;
+		if (occupid && val->occupid[dtm] && occupid != val->occupid[dtm])
+			goto done;
 
 		if (type != CMN_TYPE_WP)
 			continue;
 
 		wp_idx = arm_cmn_wp_idx(event);
-		if (val.wp[dtm][wp_idx])
-			return -EINVAL;
+		if (val->wp[dtm][wp_idx])
+			goto done;
 
-		wp_cmb = val.wp[dtm][wp_idx ^ 1];
+		wp_cmb = val->wp[dtm][wp_idx ^ 1];
 		if (wp_cmb && wp_cmb != CMN_EVENT_WP_COMBINE(event) + 1)
-			return -EINVAL;
+			goto done;
 	}
 
-	return 0;
+	ret = 0;
+done:
+	kfree(val);
+	return ret;
 }
 
 static int arm_cmn_event_init(struct perf_event *event)