Subject: Re: [PATCH net-next v11 05/12] virtio_net: Query and set flow filter caps

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 18 Nov 2025 17:06:57 -0500

On Tue, Nov 18, 2025 at 08:38:55AM -0600, Daniel Jurgens wrote:
> 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
> 
> v8:
>     - Use real_ff_mask_size when setting the selector caps. Jason Wang
> 
> v9:
>     - Set err after failed memory allocations. Simon Horman
> 
> v10:
>     - Return -EOPNOTSUPP in virnet_ff_init before allocing any memory.
>       Jason/Paolo.
> 
> v11:
>     - Return -EINVAL if any resource limit is 0. Simon Horman
>     - Ensure we don't overrun alloced space of ff->ff_mask by moving the
>       real_ff_mask_size > ff_mask_size check into the loop. Simon Horman
> ---
>  drivers/net/virtio_net.c           | 201 +++++++++++++++++++++++++++++
>  include/linux/virtio_admin.h       |   1 +
>  include/uapi/linux/virtio_net_ff.h |  91 +++++++++++++
>  3 files changed, 293 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 cfa006b88688..3615f45ac358 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 {
> @@ -6774,6 +6787,183 @@ 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;
> +
> +	if (!vdev->config->admin_cmd_exec)
> +		return -EOPNOTSUPP;
> +
> +	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) {
> +		err = -ENOMEM;
> +		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;
> +
> +	if (!ff->ff_caps->groups_limit ||
> +	    !ff->ff_caps->classifiers_limit ||
> +	    !ff->ff_caps->rules_limit ||
> +	    !ff->ff_caps->rules_per_group_limit) {
> +		err = -EINVAL;
> +		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) {
> +		err = -ENOMEM;
> +		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) {
> +		err = -ENOMEM;
> +		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];

why the cast? discards type checks for no good reason I can see.

And &...[0] is unnecessarily funky. Just plain ff->ff_mask->selectors
will do.

> +
> +	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;
> +		if (real_ff_mask_size > ff_mask_size) {
> +			err = -EINVAL;
> +			goto err_ff_action;
> +		}
> +		sel = (void *)sel + sizeof(*sel) + sel->length;

I guess the MAX_SEL_LEN check guarantees the allocation
is big enough? Let's add a BUG_ON just in case.

> +	}
> +
> +	err = virtio_admin_cap_set(vdev,
> +				   VIRTIO_NET_FF_SELECTOR_CAP,
> +				   ff->ff_mask,
> +				   real_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;
> @@ -7137,6 +7327,15 @@ 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);
> @@ -7152,6 +7351,7 @@ 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:
> @@ -7201,6 +7401,7 @@ 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

Why do it? Let net pull this header itself.

> 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

you should document in commit log that you are adding
these types to UAPI, and which spec they are from.

> @@ -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;

Ouch this is a problem. There is a 2 byte padding here.

This is a spec bug but I don't know if it is too late to fix.

Parav what do you think?

> +};
> +
> +/**
> + * 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