Subject: [PATCH net-next v7 05/12] virtio_net: Query and set flow filter caps

From: Daniel Jurgens <[email-masked]>
Date: Mon, 3 Nov 2025 16:55:07 -0600

When probing a virtnet device, attempt to read the flow filter
capabilities. In order to use the feature the caps must also
be set. For now setting what was read is sufficient.

Signed-off-by: Daniel Jurgens <[email-masked]>
Reviewed-by: Parav Pandit <[email-masked]>
Reviewed-by: Shahar Shitrit <[email-masked]>

---
v4:
    - Validate the length in the selector caps
    - Removed __free usage.
    - Removed for(int.
v5:
    - Remove unneed () after MAX_SEL_LEN macro (test bot)
v6:
    - Fix sparse warning "array of flexible structures" Jakub K/Simon H
    - Use new variable and validate ff_mask_size before set_cap. MST
v7:
    - Set ff->ff_{caps, mask, actions} NULL in error path. Paolo Abeni
    - Return errors from virtnet_ff_init, -ENOTSUPP is not fatal. Xuan
---
 drivers/net/virtio_net.c           | 185 +++++++++++++++++++++++++++++
 include/linux/virtio_admin.h       |   1 +
 include/uapi/linux/virtio_net_ff.h |  91 ++++++++++++++
 3 files changed, 277 insertions(+)
 create mode 100644 include/uapi/linux/virtio_net_ff.h

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 8e8a179aaa49..7d7390103b71 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -26,6 +26,9 @@
 #include <net/netdev_rx_queue.h>
 #include <net/netdev_queues.h>
 #include <net/xdp_sock_drv.h>
+#include <linux/virtio_admin.h>
+#include <net/ipv6.h>
+#include <net/ip.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -281,6 +284,14 @@ static const struct virtnet_stat_desc virtnet_stats_tx_speed_desc_qstat[] = {
 	VIRTNET_STATS_DESC_TX_QSTAT(speed, ratelimit_packets, hw_drop_ratelimits),
 };
 
+struct virtnet_ff {
+	struct virtio_device *vdev;
+	bool ff_supported;
+	struct virtio_net_ff_cap_data *ff_caps;
+	struct virtio_net_ff_cap_mask_data *ff_mask;
+	struct virtio_net_ff_actions *ff_actions;
+};
+
 #define VIRTNET_Q_TYPE_RX 0
 #define VIRTNET_Q_TYPE_TX 1
 #define VIRTNET_Q_TYPE_CQ 2
@@ -493,6 +504,8 @@ struct virtnet_info {
 	struct failover *failover;
 
 	u64 device_stats_cap;
+
+	struct virtnet_ff ff;
 };
 
 struct padded_vnet_hdr {
@@ -6758,6 +6771,167 @@ static const struct xdp_metadata_ops virtnet_xdp_metadata_ops = {
 	.xmo_rx_hash			= virtnet_xdp_rx_hash,
 };
 
+static size_t get_mask_size(u16 type)
+{
+	switch (type) {
+	case VIRTIO_NET_FF_MASK_TYPE_ETH:
+		return sizeof(struct ethhdr);
+	case VIRTIO_NET_FF_MASK_TYPE_IPV4:
+		return sizeof(struct iphdr);
+	case VIRTIO_NET_FF_MASK_TYPE_IPV6:
+		return sizeof(struct ipv6hdr);
+	case VIRTIO_NET_FF_MASK_TYPE_TCP:
+		return sizeof(struct tcphdr);
+	case VIRTIO_NET_FF_MASK_TYPE_UDP:
+		return sizeof(struct udphdr);
+	}
+
+	return 0;
+}
+
+#define MAX_SEL_LEN (sizeof(struct ipv6hdr))
+
+static int virtnet_ff_init(struct virtnet_ff *ff, struct virtio_device *vdev)
+{
+	size_t ff_mask_size = sizeof(struct virtio_net_ff_cap_mask_data) +
+			      sizeof(struct virtio_net_ff_selector) *
+			      VIRTIO_NET_FF_MASK_TYPE_MAX;
+	struct virtio_admin_cmd_query_cap_id_result *cap_id_list;
+	struct virtio_net_ff_selector *sel;
+	size_t real_ff_mask_size;
+	int err;
+	int i;
+
+	cap_id_list = kzalloc(sizeof(*cap_id_list), GFP_KERNEL);
+	if (!cap_id_list)
+		return -ENOMEM;
+
+	err = virtio_admin_cap_id_list_query(vdev, cap_id_list);
+	if (err)
+		goto err_cap_list;
+
+	if (!(VIRTIO_CAP_IN_LIST(cap_id_list,
+				 VIRTIO_NET_FF_RESOURCE_CAP) &&
+	      VIRTIO_CAP_IN_LIST(cap_id_list,
+				 VIRTIO_NET_FF_SELECTOR_CAP) &&
+	      VIRTIO_CAP_IN_LIST(cap_id_list,
+				 VIRTIO_NET_FF_ACTION_CAP))) {
+		err = -EOPNOTSUPP;
+		goto err_cap_list;
+	}
+
+	ff->ff_caps = kzalloc(sizeof(*ff->ff_caps), GFP_KERNEL);
+	if (!ff->ff_caps)
+		goto err_cap_list;
+
+	err = virtio_admin_cap_get(vdev,
+				   VIRTIO_NET_FF_RESOURCE_CAP,
+				   ff->ff_caps,
+				   sizeof(*ff->ff_caps));
+
+	if (err)
+		goto err_ff;
+
+	/* VIRTIO_NET_FF_MASK_TYPE start at 1 */
+	for (i = 1; i <= VIRTIO_NET_FF_MASK_TYPE_MAX; i++)
+		ff_mask_size += get_mask_size(i);
+
+	ff->ff_mask = kzalloc(ff_mask_size, GFP_KERNEL);
+	if (!ff->ff_mask)
+		goto err_ff;
+
+	err = virtio_admin_cap_get(vdev,
+				   VIRTIO_NET_FF_SELECTOR_CAP,
+				   ff->ff_mask,
+				   ff_mask_size);
+
+	if (err)
+		goto err_ff_mask;
+
+	ff->ff_actions = kzalloc(sizeof(*ff->ff_actions) +
+					VIRTIO_NET_FF_ACTION_MAX,
+					GFP_KERNEL);
+	if (!ff->ff_actions)
+		goto err_ff_mask;
+
+	err = virtio_admin_cap_get(vdev,
+				   VIRTIO_NET_FF_ACTION_CAP,
+				   ff->ff_actions,
+				   sizeof(*ff->ff_actions) + VIRTIO_NET_FF_ACTION_MAX);
+
+	if (err)
+		goto err_ff_action;
+
+	err = virtio_admin_cap_set(vdev,
+				   VIRTIO_NET_FF_RESOURCE_CAP,
+				   ff->ff_caps,
+				   sizeof(*ff->ff_caps));
+	if (err)
+		goto err_ff_action;
+
+	real_ff_mask_size = sizeof(struct virtio_net_ff_cap_mask_data);
+	sel = (void *)&ff->ff_mask->selectors[0];
+
+	for (i = 0; i < ff->ff_mask->count; i++) {
+		if (sel->length > MAX_SEL_LEN) {
+			err = -EINVAL;
+			goto err_ff_action;
+		}
+		real_ff_mask_size += sizeof(struct virtio_net_ff_selector) + sel->length;
+		sel = (void *)sel + sizeof(*sel) + sel->length;
+	}
+
+	if (real_ff_mask_size > ff_mask_size) {
+		err = -EINVAL;
+		goto err_ff_action;
+	}
+
+	err = virtio_admin_cap_set(vdev,
+				   VIRTIO_NET_FF_SELECTOR_CAP,
+				   ff->ff_mask,
+				   ff_mask_size);
+	if (err)
+		goto err_ff_action;
+
+	err = virtio_admin_cap_set(vdev,
+				   VIRTIO_NET_FF_ACTION_CAP,
+				   ff->ff_actions,
+				   sizeof(*ff->ff_actions) + VIRTIO_NET_FF_ACTION_MAX);
+	if (err)
+		goto err_ff_action;
+
+	ff->vdev = vdev;
+	ff->ff_supported = true;
+
+	kfree(cap_id_list);
+
+	return 0;
+
+err_ff_action:
+	kfree(ff->ff_actions);
+	ff->ff_actions = NULL;
+err_ff_mask:
+	kfree(ff->ff_mask);
+	ff->ff_mask = NULL;
+err_ff:
+	kfree(ff->ff_caps);
+	ff->ff_caps = NULL;
+err_cap_list:
+	kfree(cap_id_list);
+
+	return err;
+}
+
+static void virtnet_ff_cleanup(struct virtnet_ff *ff)
+{
+	if (!ff->ff_supported)
+		return;
+
+	kfree(ff->ff_actions);
+	kfree(ff->ff_mask);
+	kfree(ff->ff_caps);
+}
+
 static int virtnet_probe(struct virtio_device *vdev)
 {
 	int i, err = -ENOMEM;
@@ -7121,6 +7295,15 @@ static int virtnet_probe(struct virtio_device *vdev)
 	}
 	vi->guest_offloads_capable = vi->guest_offloads;
 
+	/* Initialize flow filters. Not supported is an acceptable and common
+	 * return code
+	 */
+	err = virtnet_ff_init(&vi->ff, vi->vdev);
+	if (err && err != -EOPNOTSUPP) {
+		rtnl_unlock();
+		goto free_unregister_netdev;
+	}
+
 	rtnl_unlock();
 
 	err = virtnet_cpu_notif_add(vi);
@@ -7136,6 +7319,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 
 free_unregister_netdev:
 	unregister_netdev(dev);
+	virtnet_ff_cleanup(&vi->ff);
 free_failover:
 	net_failover_destroy(vi->failover);
 free_vqs:
@@ -7185,6 +7369,7 @@ static void virtnet_remove(struct virtio_device *vdev)
 	virtnet_free_irq_moder(vi);
 
 	unregister_netdev(vi->dev);
+	virtnet_ff_cleanup(&vi->ff);
 
 	net_failover_destroy(vi->failover);
 
diff --git a/include/linux/virtio_admin.h b/include/linux/virtio_admin.h
index 039b996f73ec..db0f42346ca9 100644
--- a/include/linux/virtio_admin.h
+++ b/include/linux/virtio_admin.h
@@ -3,6 +3,7 @@
  * Header file for virtio admin operations
  */
 #include <uapi/linux/virtio_pci.h>
+#include <uapi/linux/virtio_net_ff.h>
 
 #ifndef _LINUX_VIRTIO_ADMIN_H
 #define _LINUX_VIRTIO_ADMIN_H
diff --git a/include/uapi/linux/virtio_net_ff.h b/include/uapi/linux/virtio_net_ff.h
new file mode 100644
index 000000000000..bd7a194a9959
--- /dev/null
+++ b/include/uapi/linux/virtio_net_ff.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
+ *
+ * Header file for virtio_net flow filters
+ */
+#ifndef _LINUX_VIRTIO_NET_FF_H
+#define _LINUX_VIRTIO_NET_FF_H
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+
+#define VIRTIO_NET_FF_RESOURCE_CAP 0x800
+#define VIRTIO_NET_FF_SELECTOR_CAP 0x801
+#define VIRTIO_NET_FF_ACTION_CAP 0x802
+
+/**
+ * struct virtio_net_ff_cap_data - Flow filter resource capability limits
+ * @groups_limit: maximum number of flow filter groups supported by the device
+ * @classifiers_limit: maximum number of classifiers supported by the device
+ * @rules_limit: maximum number of rules supported device-wide across all groups
+ * @rules_per_group_limit: maximum number of rules allowed in a single group
+ * @last_rule_priority: priority value associated with the lowest-priority rule
+ * @selectors_per_classifier_limit: maximum selectors allowed in one classifier
+ *
+ * The limits are reported by the device and describe resource capacities for
+ * flow filters. Multi-byte fields are little-endian.
+ */
+struct virtio_net_ff_cap_data {
+	__le32 groups_limit;
+	__le32 classifiers_limit;
+	__le32 rules_limit;
+	__le32 rules_per_group_limit;
+	__u8 last_rule_priority;
+	__u8 selectors_per_classifier_limit;
+};
+
+/**
+ * struct virtio_net_ff_selector - Selector mask descriptor
+ * @type: selector type, one of VIRTIO_NET_FF_MASK_TYPE_* constants
+ * @flags: selector flags, see VIRTIO_NET_FF_MASK_F_* constants
+ * @reserved: must be set to 0 by the driver and ignored by the device
+ * @length: size in bytes of @mask
+ * @reserved1: must be set to 0 by the driver and ignored by the device
+ * @mask: variable-length mask payload for @type, length given by @length
+ *
+ * A selector describes a header mask that a classifier can apply. The format
+ * of @mask depends on @type.
+ */
+struct virtio_net_ff_selector {
+	__u8 type;
+	__u8 flags;
+	__u8 reserved[2];
+	__u8 length;
+	__u8 reserved1[3];
+	__u8 mask[];
+};
+
+#define VIRTIO_NET_FF_MASK_TYPE_ETH  1
+#define VIRTIO_NET_FF_MASK_TYPE_IPV4 2
+#define VIRTIO_NET_FF_MASK_TYPE_IPV6 3
+#define VIRTIO_NET_FF_MASK_TYPE_TCP  4
+#define VIRTIO_NET_FF_MASK_TYPE_UDP  5
+#define VIRTIO_NET_FF_MASK_TYPE_MAX  VIRTIO_NET_FF_MASK_TYPE_UDP
+
+/**
+ * struct virtio_net_ff_cap_mask_data - Supported selector mask formats
+ * @count: number of entries in @selectors
+ * @reserved: must be set to 0 by the driver and ignored by the device
+ * @selectors: array of supported selector descriptors
+ */
+struct virtio_net_ff_cap_mask_data {
+	__u8 count;
+	__u8 reserved[7];
+	__u8 selectors[];
+};
+#define VIRTIO_NET_FF_MASK_F_PARTIAL_MASK (1 << 0)
+
+#define VIRTIO_NET_FF_ACTION_DROP 1
+#define VIRTIO_NET_FF_ACTION_RX_VQ 2
+#define VIRTIO_NET_FF_ACTION_MAX  VIRTIO_NET_FF_ACTION_RX_VQ
+/**
+ * struct virtio_net_ff_actions - Supported flow actions
+ * @count: number of supported actions in @actions
+ * @reserved: must be set to 0 by the driver and ignored by the device
+ * @actions: array of action identifiers (VIRTIO_NET_FF_ACTION_*)
+ */
+struct virtio_net_ff_actions {
+	__u8 count;
+	__u8 reserved[7];
+	__u8 actions[];
+};
+#endif
-- 
2.50.1