[PATCH net-next v19 08/12] virtio_net: Use existing classifier if possible

From: Daniel Jurgens <hidden>
Date: 2026-02-04 22:40:23
Also in: virtualization
Subsystem: networking drivers, the rest, virtio net driver · Maintainers: Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds, "Michael S. Tsirkin", Jason Wang

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 <redacted>
Reviewed-by: Parav Pandit <redacted>
Reviewed-by: Shahar Shitrit <redacted>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
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

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