Subject: [PATCH net-next v20 08/12] virtio_net: Use existing classifier if possible

From: Daniel Jurgens <[email-masked]>
Date: Thu, 5 Feb 2026 16:47:03 -0600

Classifiers can be used by more than one rule. If there is an existing
classifier, use it instead of creating a new one. If duplicate
classifiers are created it would artifically limit the number of rules
to the classifier limit, which is likely less than the rules limit.

Signed-off-by: Daniel Jurgens <[email-masked]>
Reviewed-by: Parav Pandit <[email-masked]>
Reviewed-by: Shahar Shitrit <[email-masked]>
Reviewed-by: Xuan Zhuo <[email-masked]>
---
v4:
    - Fixed typo in commit message
    - for (int -> for (

v8:
    - Removed unused num_classifiers. Jason Wang

v12:
    - Clarified comment about destroy_classifier freeing. MST
    - Renamed the classifier field of virtnet_classifier to obj. MST
    - Explained why in commit message. MST

v13:
    - Fixed comment about try_destroy_classifier. MST
---
---
 drivers/net/virtio_net.c | 51 ++++++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 17 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 27833ba1abee..5cbf26d8f7ad 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -32,6 +32,7 @@
 #include <uapi/linux/virtio_pci.h>
 #include <uapi/linux/virtio_net_ff.h>
 #include <linux/xarray.h>
+#include <linux/refcount.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -302,7 +303,6 @@ struct virtnet_ff {
 	struct virtio_net_ff_cap_mask_data *ff_mask;
 	struct virtio_net_ff_actions *ff_actions;
 	struct xarray classifiers;
-	int num_classifiers;
 	struct virtnet_ethtool_ff ethtool;
 };
 
@@ -5740,12 +5740,13 @@ struct virtnet_ethtool_rule {
 /* The classifier struct must be the last field in this struct */
 struct virtnet_classifier {
 	size_t size;
+	refcount_t refcount;
 	u32 id;
-	struct virtio_net_resource_obj_ff_classifier classifier;
+	struct virtio_net_resource_obj_ff_classifier obj;
 };
 
 static_assert(sizeof(struct virtnet_classifier) ==
-	      ALIGN(offsetofend(struct virtnet_classifier, classifier),
+	      ALIGN(offsetofend(struct virtnet_classifier, obj),
 		    __alignof__(struct virtnet_classifier)),
 	      "virtnet_classifier: classifier must be the last member");
 
@@ -5833,11 +5834,24 @@ static bool validate_mask(const struct virtnet_ff *ff,
 	return false;
 }
 
-static int setup_classifier(struct virtnet_ff *ff, struct virtnet_classifier *c)
+static int setup_classifier(struct virtnet_ff *ff,
+			    struct virtnet_classifier **c)
 {
+	struct virtnet_classifier *tmp;
+	unsigned long i;
 	int err;
 
-	err = xa_alloc(&ff->classifiers, &c->id, c,
+	xa_for_each(&ff->classifiers, i, tmp) {
+		if ((*c)->size == tmp->size &&
+		    !memcmp(&tmp->obj, &(*c)->obj, tmp->size)) {
+			refcount_inc(&tmp->refcount);
+			kfree(*c);
+			*c = tmp;
+			goto out;
+		}
+	}
+
+	err = xa_alloc(&ff->classifiers, &(*c)->id, *c,
 		       XA_LIMIT(0, le32_to_cpu(ff->ff_caps->classifiers_limit) - 1),
 		       GFP_KERNEL);
 	if (err)
@@ -5845,29 +5859,30 @@ static int setup_classifier(struct virtnet_ff *ff, struct virtnet_classifier *c)
 
 	err = virtio_admin_obj_create(ff->vdev,
 				      VIRTIO_NET_RESOURCE_OBJ_FF_CLASSIFIER,
-				      c->id,
+				      (*c)->id,
 				      VIRTIO_ADMIN_GROUP_TYPE_SELF,
 				      0,
-				      &c->classifier,
-				      c->size);
+				      &(*c)->obj,
+				      (*c)->size);
 	if (err)
 		goto err_xarray;
 
+	refcount_set(&(*c)->refcount, 1);
+out:
 	return 0;
 
 err_xarray:
-	xa_erase(&ff->classifiers, c->id);
+	xa_erase(&ff->classifiers, (*c)->id);
 
 	return err;
 }
 
-static void destroy_classifier(struct virtnet_ff *ff,
-			       u32 classifier_id)
+static void try_destroy_classifier(struct virtnet_ff *ff, u32 classifier_id)
 {
 	struct virtnet_classifier *c;
 
 	c = xa_load(&ff->classifiers, classifier_id);
-	if (c) {
+	if (c && refcount_dec_and_test(&c->refcount)) {
 		virtio_admin_obj_destroy(ff->vdev,
 					 VIRTIO_NET_RESOURCE_OBJ_FF_CLASSIFIER,
 					 c->id,
@@ -5891,7 +5906,7 @@ static void destroy_ethtool_rule(struct virtnet_ff *ff,
 				 0);
 
 	xa_erase(&ff->ethtool.rules, eth_rule->flow_spec.location);
-	destroy_classifier(ff, eth_rule->classifier_id);
+	try_destroy_classifier(ff, eth_rule->classifier_id);
 	kfree(eth_rule);
 }
 
@@ -6063,7 +6078,7 @@ static int build_and_insert(struct virtnet_ff *ff,
 	}
 
 	c->size = classifier_size;
-	classifier = &c->classifier;
+	classifier = &c->obj;
 	classifier->count = num_hdrs;
 	selector = (void *)&classifier->selectors[0];
 
@@ -6073,14 +6088,16 @@ static int build_and_insert(struct virtnet_ff *ff,
 	if (err)
 		goto err_classifier;
 
-	err = setup_classifier(ff, c);
+	err = setup_classifier(ff, &c);
 	if (err)
 		goto err_classifier;
 
 	err = insert_rule(ff, eth_rule, c->id, key, key_size);
 	if (err) {
-		/* destroy_classifier will free the classifier */
-		destroy_classifier(ff, c->id);
+		/* try_destroy_classifier will decrement the refcount on the
+		 * classifier and free it if needed.
+		 */
+		try_destroy_classifier(ff, c->id);
 		goto err_key;
 	}
 
-- 
2.50.1