On Fri, May 30, 2025 at 12:50 PM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote:
>
> Add common code required for the features being added to TUN and TAP.
> They will be enabled for each of them in following patches.
>
> Added Features
> ==============
>
> Hash reporting
> --------------
>
> Allow the guest to reuse the hash value to make receive steering
> consistent between the host and guest, and to save hash computation.
>
> Receive Side Scaling (RSS)
> --------------------------
>
> RSS is a receive steering algorithm that can be negotiated to use with
> virtio_net. Conventionally the hash calculation was done by the VMM.
> However, computing the hash after the queue was chosen defeats the
> purpose of RSS.
>
> Another approach is to use eBPF steering program. This approach has
> another downside: it cannot report the calculated hash due to the
> restrictive nature of eBPF steering program.
>
> Introduce the code to perform RSS to the kernel in order to overcome
> thse challenges. An alternative solution is to extend the eBPF steering
> program so that it will be able to report to the userspace, but I didn't
> opt for it because extending the current mechanism of eBPF steering
> program as is because it relies on legacy context rewriting, and
> introducing kfunc-based eBPF will result in non-UAPI dependency while
> the other relevant virtualization APIs such as KVM and vhost_net are
> UAPIs.
>
> Added ioctls
> ============
>
> They are designed to make extensibility and VM migration compatible.
> This change only adds the implementation and does not expose them to
> the userspace.
>
> TUNGETVNETHASHTYPES
> -------------------
>
> This ioctl tells supported hash types. It is useful to check if a VM can
> be migrated to the current host.
>
> TUNSETVNETREPORTINGAUTOMQ, TUNSETVNETREPORTINGRSS, and TUNSETVNETRSS
> --------------------------------------------------------------------
>
> These ioctls configures a steering algorithm and, if needed, hash
> reporting.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
> Tested-by: Lei Yang <leiyang@xxxxxxxxxx>
> ---
> drivers/net/tap.c | 10 ++-
> drivers/net/tun.c | 12 +++-
> drivers/net/tun_vnet.h | 165 +++++++++++++++++++++++++++++++++++++++++---
> include/uapi/linux/if_tun.h | 71 +++++++++++++++++++
> 4 files changed, 244 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/tap.c b/drivers/net/tap.c
> index d4ece538f1b2..25c60ff2d3f2 100644
> --- a/drivers/net/tap.c
> +++ b/drivers/net/tap.c
> @@ -179,6 +179,11 @@ static void tap_put_queue(struct tap_queue *q)
> sock_put(&q->sk);
> }
>
> +static const struct virtio_net_hash *tap_find_hash(const struct sk_buff *skb)
> +{
> + return NULL;
> +}
> +
> /*
> * Select a queue based on the rxq of the device on which this packet
> * arrived. If the incoming device is not mq, calculate a flow hash
> @@ -711,11 +716,12 @@ static ssize_t tap_put_user(struct tap_queue *q,
> int total;
>
> if (q->flags & IFF_VNET_HDR) {
> - struct virtio_net_hdr vnet_hdr;
> + struct virtio_net_hdr_v1_hash vnet_hdr;
>
> vnet_hdr_len = READ_ONCE(q->vnet_hdr_sz);
>
> - ret = tun_vnet_hdr_from_skb(q->flags, NULL, skb, &vnet_hdr);
> + ret = tun_vnet_hdr_from_skb(vnet_hdr_len, q->flags, NULL, skb,
> + tap_find_hash, &vnet_hdr);
> if (ret)
> return ret;
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 9133ab9ed3f5..03d47799e9bd 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -451,6 +451,11 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
> e->rps_rxhash = hash;
> }
>
> +static const struct virtio_net_hash *tun_find_hash(const struct sk_buff *skb)
> +{
> + return NULL;
> +}
> +
> /* We try to identify a flow through its rxhash. The reason that
> * we do not check rxq no. is because some cards(e.g 82599), chooses
> * the rxq based on the txq where the last packet of the flow comes. As
> @@ -1993,7 +1998,7 @@ static ssize_t tun_put_user_xdp(struct tun_struct *tun,
> ssize_t ret;
>
> if (tun->flags & IFF_VNET_HDR) {
> - struct virtio_net_hdr gso = { 0 };
> + struct virtio_net_hdr_v1_hash gso = { 0 };
>
> vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
> ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
> @@ -2046,9 +2051,10 @@ static ssize_t tun_put_user(struct tun_struct *tun,
> }
>
> if (vnet_hdr_sz) {
> - struct virtio_net_hdr gso;
> + struct virtio_net_hdr_v1_hash gso;
>
> - ret = tun_vnet_hdr_from_skb(tun->flags, tun->dev, skb, &gso);
> + ret = tun_vnet_hdr_from_skb(vnet_hdr_sz, tun->flags, tun->dev,
> + skb, tun_find_hash, &gso);
> if (ret)
> return ret;
>
> diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
> index 58b9ac7a5fc4..45d0533efc8d 100644
> --- a/drivers/net/tun_vnet.h
> +++ b/drivers/net/tun_vnet.h
> @@ -6,6 +6,17 @@
> #define TUN_VNET_LE 0x80000000
> #define TUN_VNET_BE 0x40000000
>
> +typedef struct virtio_net_hash *(*tun_vnet_hash_add)(struct sk_buff *);
> +typedef const struct virtio_net_hash *(*tun_vnet_hash_find)(const struct sk_buff *);
> +
> +struct tun_vnet_hash {
> + bool report;
> + bool rss;
> + struct tun_vnet_rss common;
> + u32 rss_key[VIRTIO_NET_RSS_MAX_KEY_SIZE];
> + u16 rss_indirection_table[];
> +};
> +
> static inline bool tun_vnet_legacy_is_little_endian(unsigned int flags)
> {
> bool be = IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) &&
> @@ -107,6 +118,128 @@ static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
> }
> }
>
> +static inline long tun_vnet_ioctl_gethashtypes(u32 __user *argp)
> +{
> + return put_user(VIRTIO_NET_SUPPORTED_HASH_TYPES, argp) ? -EFAULT : 0;
> +}
> +
> +static inline long tun_vnet_ioctl_sethash(struct tun_vnet_hash __rcu **hashp,
> + unsigned int cmd,
> + void __user *argp)
> +{
> + struct tun_vnet_rss common;
> + struct tun_vnet_hash *hash;
> + size_t indirection_table_size;
> + size_t key_size;
> + size_t size;
> +
> + switch (cmd) {
> + case TUNSETVNETREPORTINGAUTOMQ:
> + if (get_user(common.hash_types, (u32 __user *)argp))
> + return -EFAULT;
> +
> + if (common.hash_types) {
> + hash = kzalloc(sizeof(*hash), GFP_KERNEL);
> + if (!hash)
> + return -ENOMEM;
> +
> + hash->report = true;
> + hash->common.hash_types = common.hash_types;
> + } else {
> + hash = NULL;
> + }
> + break;
> +
> + case TUNSETVNETREPORTINGRSS:
> + case TUNSETVNETRSS:
So the above three shows unnecessary design redundancy as well as a
burden for the future extension. Why not simply have
1) TUNSETVNET_RSS
2) TUNSETVNET_HASH_REPORT
?
Which maps to
#define VIRTIO_NET_CTRL_MQ_RSS_CONFIG 1 (for configurable
receive steering)
#define VIRTIO_NET_CTRL_MQ_HASH_CONFIG 2 (for configurable
hash calculation)
It would be always easier to start with what spec had or at least we
need to explain why we choose a different design here or in the
changelog to ease our life.
One day we would have tun_select_queue_algorithm_x() we don't have to
duplicate the ioctls once again here like TUNSETVNETREPORTINGXYZ
> + if (copy_from_user(&common, argp, sizeof(common)))
> + return -EFAULT;
> + argp = (struct tun_vnet_rss __user *)argp + 1;
> +
> + indirection_table_size = ((size_t)common.indirection_table_mask + 1) * 2;
> + key_size = virtio_net_hash_key_length(common.hash_types);
> + size = struct_size(hash, rss_indirection_table,
> + (size_t)common.indirection_table_mask + 1);
> +
> + hash = kmalloc(size, GFP_KERNEL);
> + if (!hash)
> + return -ENOMEM;
> +
> + if (copy_from_user(hash->rss_indirection_table,
> + argp, indirection_table_size)) {
> + kfree(hash);
> + return -EFAULT;
> + }
> + argp = (u16 __user *)argp + common.indirection_table_mask + 1;
> +
> + if (copy_from_user(hash->rss_key, argp, key_size)) {
> + kfree(hash);
> + return -EFAULT;
> + }
> +
> + virtio_net_toeplitz_convert_key(hash->rss_key, key_size);
> + hash->report = cmd == TUNSETVNETREPORTINGRSS;
At least, if this is the only difference why not simply code this into
the ioctl itself other than having a very similar command?
> + hash->rss = true;
> + hash->common = common;
> + break;
> +
> + default:
> + return -EINVAL;
> + }
> +
> + kfree_rcu_mightsleep(rcu_replace_pointer_rtnl(*hashp, hash));
> + return 0;
> +}
> +
> +static inline void tun_vnet_hash_report(const struct tun_vnet_hash *hash,
> + struct sk_buff *skb,
> + const struct flow_keys_basic *keys,
> + u32 value,
> + tun_vnet_hash_add vnet_hash_add)
> +{
> + struct virtio_net_hash *report;
> +
> + if (!hash || !hash->report)
> + return;
> +
> + report = vnet_hash_add(skb);
> + if (!report)
> + return;
> +
> + *report = (struct virtio_net_hash) {
> + .report = virtio_net_hash_report(hash->common.hash_types, keys),
> + .value = value
> + };
> +}
> +
> +static inline u16 tun_vnet_rss_select_queue(u32 numqueues,
> + const struct tun_vnet_hash *hash,
> + struct sk_buff *skb,
> + tun_vnet_hash_add vnet_hash_add)
> +{
> + struct virtio_net_hash *report;
> + struct virtio_net_hash ret;
> + u16 index;
> +
> + if (!numqueues)
> + return 0;
> +
> + virtio_net_hash_rss(skb, hash->common.hash_types, hash->rss_key, &ret);
> +
> + if (!ret.report)
> + return hash->common.unclassified_queue % numqueues;
> +
> + if (hash->report) {
> + report = vnet_hash_add(skb);
> + if (report)
> + *report = ret;
> + }
> +
> + index = ret.value & hash->common.indirection_table_mask;
> +
> + return hash->rss_indirection_table[index] % numqueues;
> +}
> +
> static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
> struct iov_iter *from,
> struct virtio_net_hdr *hdr)
> @@ -135,15 +268,17 @@ static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
> }
>
> static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter,
> - const struct virtio_net_hdr *hdr)
> + const struct virtio_net_hdr_v1_hash *hdr)
> {
> + int content_sz = MIN(sizeof(*hdr), sz);
> +
> if (unlikely(iov_iter_count(iter) < sz))
> return -EINVAL;
>
> - if (unlikely(copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr)))
> + if (unlikely(copy_to_iter(hdr, content_sz, iter) != content_sz))
> return -EFAULT;
>
> - if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr))
> + if (iov_iter_zero(sz - content_sz, iter) != sz - content_sz)
> return -EFAULT;
>
> return 0;
> @@ -155,26 +290,38 @@ static inline int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb,
> return virtio_net_hdr_to_skb(skb, hdr, tun_vnet_is_little_endian(flags));
> }
>
> -static inline int tun_vnet_hdr_from_skb(unsigned int flags,
> +static inline int tun_vnet_hdr_from_skb(int sz, unsigned int flags,
> const struct net_device *dev,
> const struct sk_buff *skb,
> - struct virtio_net_hdr *hdr)
> + tun_vnet_hash_find vnet_hash_find,
> + struct virtio_net_hdr_v1_hash *hdr)
> {
> int vlan_hlen = skb_vlan_tag_present(skb) ? VLAN_HLEN : 0;
> + const struct virtio_net_hash *report = sz < sizeof(struct virtio_net_hdr_v1_hash) ?
> + NULL : vnet_hash_find(skb);
> +
> + *hdr = (struct virtio_net_hdr_v1_hash) {
> + .hash_report = VIRTIO_NET_HASH_REPORT_NONE
> + };
> +
> + if (report) {
> + hdr->hash_value = cpu_to_le32(report->value);
> + hdr->hash_report = cpu_to_le16(report->report);
> + }
>
> - if (virtio_net_hdr_from_skb(skb, hdr,
> + if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)hdr,
> tun_vnet_is_little_endian(flags), true,
> vlan_hlen)) {
> struct skb_shared_info *sinfo = skb_shinfo(skb);
>
> if (net_ratelimit()) {
> netdev_err(dev, "unexpected GSO type: 0x%x, gso_size %d, hdr_len %d\n",
> - sinfo->gso_type, tun_vnet16_to_cpu(flags, hdr->gso_size),
> - tun_vnet16_to_cpu(flags, hdr->hdr_len));
> + sinfo->gso_type, tun_vnet16_to_cpu(flags, hdr->hdr.gso_size),
> + tun_vnet16_to_cpu(flags, hdr->hdr.hdr_len));
> print_hex_dump(KERN_ERR, "tun: ",
> DUMP_PREFIX_NONE,
> 16, 1, skb->head,
> - min(tun_vnet16_to_cpu(flags, hdr->hdr_len), 64), true);
> + min(tun_vnet16_to_cpu(flags, hdr->hdr.hdr_len), 64), true);
> }
> WARN_ON_ONCE(1);
> return -EINVAL;
> diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
> index 980de74724fc..fe4b984d3bbb 100644
> --- a/include/uapi/linux/if_tun.h
> +++ b/include/uapi/linux/if_tun.h
> @@ -62,6 +62,62 @@
> #define TUNSETCARRIER _IOW('T', 226, int)
> #define TUNGETDEVNETNS _IO('T', 227)
>
> +/**
> + * define TUNGETVNETHASHTYPES - ioctl to get supported virtio_net hashing types
> + *
> + * The argument is a pointer to __u32 which will store the supported virtio_net
> + * hashing types.
> + */
> +#define TUNGETVNETHASHTYPES _IOR('T', 228, __u32)
> +
> +/**
> + * define TUNSETVNETREPORTINGAUTOMQ - ioctl to enable automq with hash reporting
> + *
> + * Disable RSS and enable automatic receive steering with hash reporting.
> + *
> + * The argument is a pointer to __u32 that contains a bitmask of hash types
> + * allowed to be reported.
> + *
> + * This ioctl results in %EBADFD if the underlying device is deleted. It affects
> + * all queues attached to the same device.
> + *
> + * This ioctl currently has no effect on XDP packets and packets with
> + * queue_mapping set by TC.
> + */
> +#define TUNSETVNETREPORTINGAUTOMQ _IOR('T', 229, __u32)
> +
> +/**
> + * define TUNSETVNETREPORTINGRSS - ioctl to enable RSS with hash reporting
> + *
> + * Disable automatic receive steering and enable RSS with hash reporting.
This is unnecessary, e.g one day will have select_queue_xyz(), we
don't want to say "Disable automatic receive steering and xyz ..."
> + *
> + * This ioctl results in %EBADFD if the underlying device is deleted. It affects
> + * all queues attached to the same device.
> + *
> + * This ioctl currently has no effect on XDP packets and packets with
> + * queue_mapping set by TC.
> + */
> +#define TUNSETVNETREPORTINGRSS _IOR('T', 230, struct tun_vnet_rss)
> +
> +/**
> + * define TUNSETVNETRSS - ioctl to enable RSS without hash reporting
> + *
> + * Disable automatic receive steering and enable RSS without hash reporting.
Same here.
> + *
> + * The argument is a pointer to the compound of the following in order:
> + *
> + * 1. &struct tun_vnet_rss
> + * 3. Indirection table
> + * 4. Key
> + *
> + * This ioctl results in %EBADFD if the underlying device is deleted. It affects
> + * all queues attached to the same device.
> + *
> + * This ioctl currently has no effect on XDP packets and packets with
> + * queue_mapping set by TC.
> + */
> +#define TUNSETVNETRSS _IOR('T', 231, struct tun_vnet_rss)
> +
> /* TUNSETIFF ifr flags */
> #define IFF_TUN 0x0001
> #define IFF_TAP 0x0002
> @@ -124,4 +180,19 @@ struct tun_filter {
> */
> #define TUN_STEERINGEBPF_FALLBACK -1
>
> +/**
> + * struct tun_vnet_rss - virtio_net RSS configuration
> + * @hash_types:
> + * Bitmask of allowed hash types
> + * @indirection_table_mask:
> + * Bitmask to be applied to the indirection table index
> + * @unclassified_queue:
> + * The index of the queue to place unclassified packets in
> + */
> +struct tun_vnet_rss {
> + __u32 hash_types;
> + __u16 indirection_table_mask;
> + __u16 unclassified_queue;
> +};
> +
> #endif /* _UAPI__IF_TUN_H */
>
> --
> 2.49.0
>
Thanks
