Message-Id: <20250228-rss-v7-3-844205cbbdd6@daynix.com>
Date: Fri, 28 Feb 2025 16:58:49 +0900
From: Akihiko Odaki <akihiko.odaki@...nix.com>
To: Jonathan Corbet <corbet@....net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Jason Wang <jasowang@...hat.com>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, 
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Shuah Khan <shuah@...nel.org>, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 netdev@...r.kernel.org, kvm@...r.kernel.org, 
 virtualization@...ts.linux-foundation.org, linux-kselftest@...r.kernel.org, 
 Yuri Benditovich <yuri.benditovich@...nix.com>, 
 Andrew Melnychenko <andrew@...nix.com>, 
 Stephen Hemminger <stephen@...workplumber.org>, gur.stavi@...wei.com, 
 Lei Yang <leiyang@...hat.com>, Akihiko Odaki <akihiko.odaki@...nix.com>
Subject: [PATCH net-next v7 3/6] tun: Introduce virtio-net hash feature

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.

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.

Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
---
 Documentation/networking/tuntap.rst |   7 ++
 drivers/net/Kconfig                 |   1 +
 drivers/net/tap.c                   |  62 ++++++++++++-
 drivers/net/tun.c                   |  89 ++++++++++++++----
 drivers/net/tun_vnet.h              | 180 +++++++++++++++++++++++++++++++++---
 include/linux/if_tap.h              |   2 +
 include/linux/skbuff.h              |   3 +
 include/uapi/linux/if_tun.h         |  75 +++++++++++++++
 net/core/skbuff.c                   |   4 +
 9 files changed, 390 insertions(+), 33 deletions(-)

diff --git a/Documentation/networking/tuntap.rst b/Documentation/networking/tuntap.rst
index 4d7087f727be5e37dfbf5066a9e9c872cc98898d..86b4ae8caa8ad062c1e558920be42ce0d4217465 100644
--- a/Documentation/networking/tuntap.rst
+++ b/Documentation/networking/tuntap.rst
@@ -206,6 +206,13 @@ enable is true we enable it, otherwise we disable it::
       return ioctl(fd, TUNSETQUEUE, (void *)&ifr);
   }
 
+3.4 Reference
+-------------
+
+``linux/if_tun.h`` defines the interface described below:
+
+.. kernel-doc:: include/uapi/linux/if_tun.h
+
 Universal TUN/TAP device driver Frequently Asked Question
 =========================================================
 
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 1fd5acdc73c6af0e1a861867039c3624fc618e25..aecfd244dd83585fea2c5b815dcd787c58166c28 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -395,6 +395,7 @@ config TUN
 	tristate "Universal TUN/TAP device driver support"
 	depends on INET
 	select CRC32
+	select SKB_EXTENSIONS
 	help
 	  TUN/TAP provides packet reception and transmission for user space
 	  programs.  It can be viewed as a simple Point-to-Point or Ethernet
diff --git a/drivers/net/tap.c b/drivers/net/tap.c
index d4ece538f1b23789ca60caa6232690e4d0a4d14a..06c6df153a30a4acbcaff8619b0b4229eb638664 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -49,6 +49,10 @@ struct major_info {
 	struct list_head next;
 };
 
+struct tap_skb_cb {
+	struct virtio_net_hash hash;
+};
+
 #define GOODCOPY_LEN 128
 
 static const struct proto_ops tap_socket_ops;
@@ -179,6 +183,22 @@ static void tap_put_queue(struct tap_queue *q)
 	sock_put(&q->sk);
 }
 
+static struct tap_skb_cb *tap_skb_cb(const struct sk_buff *skb)
+{
+	BUILD_BUG_ON(sizeof(skb->cb) < sizeof(struct tap_skb_cb));
+	return (struct tap_skb_cb *)skb->cb;
+}
+
+static struct virtio_net_hash *tap_add_hash(struct sk_buff *skb)
+{
+	return &tap_skb_cb(skb)->hash;
+}
+
+static const struct virtio_net_hash *tap_find_hash(const struct sk_buff *skb)
+{
+	return &tap_skb_cb(skb)->hash;
+}
+
 /*
  * 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
@@ -189,6 +209,7 @@ static void tap_put_queue(struct tap_queue *q)
 static struct tap_queue *tap_get_queue(struct tap_dev *tap,
 				       struct sk_buff *skb)
 {
+	struct flow_keys_basic keys_basic;
 	struct tap_queue *queue = NULL;
 	/* Access to taps array is protected by rcu, but access to numvtaps
 	 * isn't. Below we use it to lookup a queue, but treat it as a hint
@@ -196,17 +217,43 @@ static struct tap_queue *tap_get_queue(struct tap_dev *tap,
 	 * racing against queue removal.
 	 */
 	int numvtaps = READ_ONCE(tap->numvtaps);
+	struct tun_vnet_hash_container *vnet_hash = rcu_dereference(tap->vnet_hash);
 	__u32 rxq;
 
+	*tap_skb_cb(skb) = (struct tap_skb_cb) {
+		.hash = { .report = VIRTIO_NET_HASH_REPORT_NONE }
+	};
+
 	if (!numvtaps)
 		goto out;
 
 	if (numvtaps == 1)
 		goto single;
 
+	if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_RSS)) {
+		rxq = tun_vnet_rss_select_queue(numvtaps, vnet_hash, skb, tap_add_hash);
+		queue = rcu_dereference(tap->taps[rxq]);
+		goto out;
+	}
+
+	if (!skb->l4_hash && !skb->sw_hash) {
+		struct flow_keys keys;
+
+		skb_flow_dissect_flow_keys(skb, &keys, FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+		rxq = flow_hash_from_keys(&keys);
+		keys_basic = (struct flow_keys_basic) {
+			.control = keys.control,
+			.basic = keys.basic
+		};
+	} else {
+		skb_flow_dissect_flow_keys_basic(NULL, skb, &keys_basic, NULL, 0, 0, 0,
+						 FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+		rxq = skb->hash;
+	}
+
 	/* Check if we can use flow to select a queue */
-	rxq = skb_get_hash(skb);
 	if (rxq) {
+		tun_vnet_hash_report(vnet_hash, skb, &keys_basic, rxq, tap_add_hash);
 		queue = rcu_dereference(tap->taps[rxq % numvtaps]);
 		goto out;
 	}
@@ -711,11 +758,12 @@ 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;
 
@@ -1023,7 +1071,13 @@ static long tap_ioctl(struct file *file, unsigned int cmd,
 		return ret;
 
 	default:
-		return tun_vnet_ioctl(&q->vnet_hdr_sz, &q->flags, cmd, sp);
+		rtnl_lock();
+		tap = rtnl_dereference(q->tap);
+		ret = tun_vnet_ioctl(&q->vnet_hdr_sz, &q->flags,
+				     tap ? &tap->vnet_hash : NULL, -EINVAL,
+				     true, cmd, sp);
+		rtnl_unlock();
+		return ret;
 	}
 }
 
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index d8f4d3e996a7a81d1f8b04635054081671a14f07..8c9dd87ddce023baa94ab858ceed0d67dd9527da 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -209,6 +209,7 @@ struct tun_struct {
 	struct bpf_prog __rcu *xdp_prog;
 	struct tun_prog __rcu *steering_prog;
 	struct tun_prog __rcu *filter_prog;
+	struct tun_vnet_hash_container __rcu *vnet_hash;
 	struct ethtool_link_ksettings link_ksettings;
 	/* init args */
 	struct file *file;
@@ -451,20 +452,37 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
 		e->rps_rxhash = hash;
 }
 
+static struct virtio_net_hash *tun_add_hash(struct sk_buff *skb)
+{
+	return skb_ext_add(skb, SKB_EXT_TUN_VNET_HASH);
+}
+
+static const struct virtio_net_hash *tun_find_hash(const struct sk_buff *skb)
+{
+	return skb_ext_find(skb, SKB_EXT_TUN_VNET_HASH);
+}
+
 /* 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
  * the userspace application move between processors, we may get a
  * different rxq no. here.
  */
-static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
+static u16 tun_automq_select_queue(struct tun_struct *tun,
+				   const struct tun_vnet_hash_container *vnet_hash,
+				   struct sk_buff *skb)
 {
+	struct flow_keys keys;
+	struct flow_keys_basic keys_basic;
 	struct tun_flow_entry *e;
 	u32 txq, numqueues;
 
 	numqueues = READ_ONCE(tun->numqueues);
 
-	txq = __skb_get_hash_symmetric(skb);
+	memset(&keys, 0, sizeof(keys));
+	skb_flow_dissect(skb, &flow_keys_dissector_symmetric, &keys, 0);
+
+	txq = flow_hash_from_keys(&keys);
 	e = tun_flow_find(&tun->flows[tun_hashfn(txq)], txq);
 	if (e) {
 		tun_flow_save_rps_rxhash(e, txq);
@@ -473,6 +491,13 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
 		txq = reciprocal_scale(txq, numqueues);
 	}
 
+	keys_basic = (struct flow_keys_basic) {
+		.control = keys.control,
+		.basic = keys.basic
+	};
+	tun_vnet_hash_report(vnet_hash, skb, &keys_basic, skb->l4_hash ? skb->hash : txq,
+			     tun_add_hash);
+
 	return txq;
 }
 
@@ -500,10 +525,17 @@ static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb,
 	u16 ret;
 
 	rcu_read_lock();
-	if (rcu_dereference(tun->steering_prog))
+	if (rcu_dereference(tun->steering_prog)) {
 		ret = tun_ebpf_select_queue(tun, skb);
-	else
-		ret = tun_automq_select_queue(tun, skb);
+	} else {
+		struct tun_vnet_hash_container *vnet_hash = rcu_dereference(tun->vnet_hash);
+
+		if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_RSS))
+			ret = tun_vnet_rss_select_queue(READ_ONCE(tun->numqueues), vnet_hash,
+							skb, tun_add_hash);
+		else
+			ret = tun_automq_select_queue(tun, vnet_hash, skb);
+	}
 	rcu_read_unlock();
 
 	return ret;
@@ -1987,7 +2019,7 @@ 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);
@@ -2040,9 +2072,10 @@ 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;
 
@@ -2223,6 +2256,9 @@ static void tun_free_netdev(struct net_device *dev)
 	security_tun_dev_free_security(tun->security);
 	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
 	__tun_set_ebpf(tun, &tun->filter_prog, NULL);
+	rtnl_lock();
+	kfree_rcu_mightsleep(rtnl_dereference(tun->vnet_hash));
+	rtnl_unlock();
 }
 
 static void tun_setup(struct net_device *dev)
@@ -2921,13 +2957,9 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr)
 }
 
 static int tun_set_ebpf(struct tun_struct *tun, struct tun_prog __rcu **prog_p,
-			void __user *data)
+			int fd)
 {
 	struct bpf_prog *prog;
-	int fd;
-
-	if (copy_from_user(&fd, data, sizeof(fd)))
-		return -EFAULT;
 
 	if (fd == -1) {
 		prog = NULL;
@@ -2994,6 +3026,7 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 	int sndbuf;
 	int ret;
 	bool do_notify = false;
+	struct tun_vnet_hash_container *vnet_hash;
 
 	if (cmd == TUNSETIFF || cmd == TUNSETQUEUE ||
 	    (_IOC_TYPE(cmd) == SOCK_IOC_TYPE && cmd != SIOCGSKNS)) {
@@ -3052,9 +3085,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		goto unlock;
 	}
 
-	ret = -EBADFD;
-	if (!tun)
+	if (!tun) {
+		ret = tun_vnet_ioctl(NULL, NULL, NULL, -EBADFD, true, cmd, argp);
 		goto unlock;
+	}
 
 	netif_info(tun, drv, tun->dev, "tun_chr_ioctl cmd %u\n", cmd);
 
@@ -3230,11 +3264,27 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		break;
 
 	case TUNSETSTEERINGEBPF:
-		ret = tun_set_ebpf(tun, &tun->steering_prog, argp);
+		if (get_user(ret, (int __user *)argp)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		vnet_hash = rtnl_dereference(tun->vnet_hash);
+		if (ret != -1 && vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_RSS)) {
+			ret = -EBUSY;
+			break;
+		}
+
+		ret = tun_set_ebpf(tun, &tun->steering_prog, ret);
 		break;
 
 	case TUNSETFILTEREBPF:
-		ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
+		if (get_user(ret, (int __user *)argp)) {
+			ret = -EFAULT;
+			break;
+		}
+
+		ret = tun_set_ebpf(tun, &tun->filter_prog, ret);
 		break;
 
 	case TUNSETCARRIER:
@@ -3253,7 +3303,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
 		break;
 
 	default:
-		ret = tun_vnet_ioctl(&tun->vnet_hdr_sz, &tun->flags, cmd, argp);
+		ret = tun_vnet_ioctl(&tun->vnet_hdr_sz, &tun->flags,
+				     &tun->vnet_hash, -EINVAL,
+				     !rtnl_dereference(tun->steering_prog),
+				     cmd, argp);
 		break;
 	}
 
diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index 58b9ac7a5fc4084c789fe94fe36b5f8631bf1fa4..c73d778f76e33fddc6ab881bf6fbaaebc55ee9bf 100644
--- a/drivers/net/tun_vnet.h
+++ b/drivers/net/tun_vnet.h
@@ -6,6 +6,16 @@
 #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_container {
+	struct tun_vnet_hash common;
+	struct tun_vnet_hash_rss rss;
+	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) &&
@@ -61,18 +71,33 @@ static inline __virtio16 cpu_to_tun_vnet16(unsigned int flags, u16 val)
 }
 
 static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
-				  unsigned int cmd, int __user *sp)
+				  struct tun_vnet_hash_container __rcu **hashp,
+				  long fallback, bool can_rss,
+				  unsigned int cmd, void __user *argp)
 {
+	static const struct tun_vnet_hash cap = {
+		.flags = TUN_VNET_HASH_REPORT | TUN_VNET_HASH_RSS,
+		.types = VIRTIO_NET_SUPPORTED_HASH_TYPES
+	};
+	struct tun_vnet_hash hash_buf;
+	struct tun_vnet_hash_container *hash;
+	int __user *sp = argp;
 	int s;
 
 	switch (cmd) {
 	case TUNGETVNETHDRSZ:
+		if (!vnet_hdr_sz)
+			return -EBADFD;
+
 		s = *vnet_hdr_sz;
 		if (put_user(s, sp))
 			return -EFAULT;
 		return 0;
 
 	case TUNSETVNETHDRSZ:
+		if (!vnet_hdr_sz)
+			return -EBADFD;
+
 		if (get_user(s, sp))
 			return -EFAULT;
 		if (s < (int)sizeof(struct virtio_net_hdr))
@@ -82,12 +107,18 @@ static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
 		return 0;
 
 	case TUNGETVNETLE:
+		if (!flags)
+			return -EBADFD;
+
 		s = !!(*flags & TUN_VNET_LE);
 		if (put_user(s, sp))
 			return -EFAULT;
 		return 0;
 
 	case TUNSETVNETLE:
+		if (!flags)
+			return -EBADFD;
+
 		if (get_user(s, sp))
 			return -EFAULT;
 		if (s)
@@ -97,16 +128,129 @@ static inline long tun_vnet_ioctl(int *vnet_hdr_sz, unsigned int *flags,
 		return 0;
 
 	case TUNGETVNETBE:
+		if (!flags)
+			return -EBADFD;
+
 		return tun_get_vnet_be(*flags, sp);
 
 	case TUNSETVNETBE:
+		if (!flags)
+			return -EBADFD;
+
 		return tun_set_vnet_be(flags, sp);
 
+	case TUNGETVNETHASHCAP:
+		return copy_to_user(argp, &cap, sizeof(cap)) ? -EFAULT : 0;
+
+	case TUNSETVNETHASH:
+		if (!hashp)
+			return -EBADFD;
+
+		if (copy_from_user(&hash_buf, argp, sizeof(hash_buf)))
+			return -EFAULT;
+		argp = (struct tun_vnet_hash __user *)argp + 1;
+
+		if (hash_buf.flags & TUN_VNET_HASH_RSS) {
+			struct tun_vnet_hash_rss rss;
+			size_t indirection_table_size;
+			size_t key_size;
+			size_t size;
+
+			if (!can_rss)
+				return -EBUSY;
+
+			if (copy_from_user(&rss, argp, sizeof(rss)))
+				return -EFAULT;
+			argp = (struct tun_vnet_hash_rss __user *)argp + 1;
+
+			indirection_table_size = ((size_t)rss.indirection_table_mask + 1) * 2;
+			key_size = virtio_net_hash_key_length(hash_buf.types);
+			size = struct_size(hash, rss_indirection_table,
+					   (size_t)rss.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 + rss.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->rss = rss;
+		} else {
+			hash = kmalloc(sizeof(hash->common), GFP_KERNEL);
+			if (!hash)
+				return -ENOMEM;
+		}
+
+		hash->common = hash_buf;
+		kfree_rcu_mightsleep(rcu_replace_pointer_rtnl(*hashp, hash));
+		return 0;
+
 	default:
-		return -EINVAL;
+		return fallback;
 	}
 }
 
+static void tun_vnet_hash_report(const struct tun_vnet_hash_container *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->common.flags & TUN_VNET_HASH_REPORT))
+		return;
+
+	report = vnet_hash_add(skb);
+	if (!report)
+		return;
+
+	*report = (struct virtio_net_hash) {
+		.report = virtio_net_hash_report(hash->common.types, keys),
+		.value = value
+	};
+}
+
+static u16 tun_vnet_rss_select_queue(u32 numqueues,
+				     const struct tun_vnet_hash_container *hash,
+				     struct sk_buff *skb,
+				     tun_vnet_hash_add vnet_hash_add)
+{
+	struct virtio_net_hash *report;
+	struct virtio_net_hash ret;
+	u16 txq, index;
+
+	if (!numqueues)
+		return 0;
+
+	virtio_net_hash_rss(skb, hash->common.types, hash->rss_key, &ret);
+
+	if (!ret.report)
+		return hash->rss.unclassified_queue % numqueues;
+
+	if (hash->common.flags & TUN_VNET_HASH_REPORT) {
+		report = vnet_hash_add(skb);
+		if (report)
+			*report = ret;
+	}
+
+	index = ret.value & hash->rss.indirection_table_mask;
+	txq = READ_ONCE(hash->rss_indirection_table[index]);
+
+	return txq % numqueues;
+}
+
 static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
 				   struct iov_iter *from,
 				   struct virtio_net_hdr *hdr)
@@ -135,15 +279,17 @@ 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 +301,38 @@ 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/linux/if_tap.h b/include/linux/if_tap.h
index 553552fa635c3e1e53d1a63c203d32e4c4fd5a4f..7334c46a3f101675a0d4e5a036987cfe18842f9f 100644
--- a/include/linux/if_tap.h
+++ b/include/linux/if_tap.h
@@ -31,6 +31,7 @@ static inline struct ptr_ring *tap_get_ptr_ring(struct file *f)
 #define MAX_TAP_QUEUES 256
 
 struct tap_queue;
+struct tun_vnet_hash_container;
 
 struct tap_dev {
 	struct net_device	*dev;
@@ -43,6 +44,7 @@ struct tap_dev {
 	int			numqueues;
 	netdev_features_t	tap_features;
 	int			minor;
+	struct tun_vnet_hash_container __rcu *vnet_hash;
 
 	void (*update_features)(struct tap_dev *tap, netdev_features_t features);
 	void (*count_tx_dropped)(struct tap_dev *tap);
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index bb2b751d274acff931281a72e8b4b0c699b4e8af..cdd793f1c360ad5f63fcc4cbf67d845f5e2ccf6f 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -4842,6 +4842,9 @@ enum skb_ext_id {
 #endif
 #if IS_ENABLED(CONFIG_MCTP_FLOWS)
 	SKB_EXT_MCTP,
+#endif
+#if IS_ENABLED(CONFIG_TUN)
+	SKB_EXT_TUN_VNET_HASH,
 #endif
 	SKB_EXT_NUM, /* must be last */
 };
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 287cdc81c9390c289a30545aa7ed23d81c3329d3..4887f97500a870c7ef3c96a5837b2d0a5a225040 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -62,6 +62,42 @@
 #define TUNSETCARRIER _IOW('T', 226, int)
 #define TUNGETDEVNETNS _IO('T', 227)
 
+/**
+ * define TUNGETVNETHASHCAP - ioctl to get virtio_net hashing capability.
+ *
+ * The argument is a pointer to &struct tun_vnet_hash which will store the
+ * maximal virtio_net hashing configuration.
+ */
+#define TUNGETVNETHASHCAP _IOR('T', 228, struct tun_vnet_hash)
+
+/**
+ * define TUNSETVNETHASH - ioctl to configure virtio_net hashing
+ *
+ * The argument is a pointer to &struct tun_vnet_hash.
+ *
+ * The argument is a pointer to the compound of the following in order if
+ * %TUN_VNET_HASH_RSS is set:
+ *
+ * 1. &struct tun_vnet_hash
+ * 2. &struct tun_vnet_hash_rss
+ * 3. Indirection table
+ * 4. Key
+ *
+ * The %TUN_VNET_HASH_REPORT flag set with this ioctl will be effective only
+ * after calling the %TUNSETVNETHDRSZ ioctl with a number greater than or equal
+ * to the size of &struct virtio_net_hdr_v1_hash.
+ *
+ * The members added to the legacy header by %TUN_VNET_HASH_REPORT flag will
+ * always be little-endian.
+ *
+ * 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 TUNSETVNETHASH _IOW('T', 229, struct tun_vnet_hash)
+
 /* TUNSETIFF ifr flags */
 #define IFF_TUN		0x0001
 #define IFF_TAP		0x0002
@@ -115,4 +151,43 @@ struct tun_filter {
 	__u8   addr[][ETH_ALEN];
 };
 
+/**
+ * define TUN_VNET_HASH_REPORT - Request virtio_net hash reporting for vhost
+ */
+#define TUN_VNET_HASH_REPORT	0x0001
+
+/**
+ * define TUN_VNET_HASH_RSS - Request virtio_net RSS
+ *
+ * This is mutually exclusive with eBPF steering program.
+ */
+#define TUN_VNET_HASH_RSS	0x0002
+
+/**
+ * struct tun_vnet_hash - virtio_net hashing configuration
+ * @flags:
+ *		Bitmask consists of %TUN_VNET_HASH_REPORT and %TUN_VNET_HASH_RSS
+ * @pad:
+ *		Should be filled with zero before passing to %TUNSETVNETHASH
+ * @types:
+ *		Bitmask of allowed hash types
+ */
+struct tun_vnet_hash {
+	__u16 flags;
+	__u8 pad[2];
+	__u32 types;
+};
+
+/**
+ * struct tun_vnet_hash_rss - virtio_net RSS configuration
+ * @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_hash_rss {
+	__u16 indirection_table_mask;
+	__u16 unclassified_queue;
+};
+
 #endif /* _UAPI__IF_TUN_H */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7b03b64fdcb276f68ce881d1d8da8e4c6b897efc..aa2a091b649f0c9d6e0196f34f345ba78b5498fb 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -64,6 +64,7 @@
 #include <linux/mpls.h>
 #include <linux/kcov.h>
 #include <linux/iov_iter.h>
+#include <linux/virtio_net.h>
 
 #include <net/protocol.h>
 #include <net/dst.h>
@@ -4969,6 +4970,9 @@ static const u8 skb_ext_type_len[] = {
 #if IS_ENABLED(CONFIG_MCTP_FLOWS)
 	[SKB_EXT_MCTP] = SKB_EXT_CHUNKSIZEOF(struct mctp_flow),
 #endif
+#if IS_ENABLED(CONFIG_TUN)
+	[SKB_EXT_TUN_VNET_HASH] = SKB_EXT_CHUNKSIZEOF(struct virtio_net_hash),
+#endif
 };
 
 static __always_inline unsigned int skb_ext_total_length(void)

-- 
2.48.1

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