[PATCH RFC v5 06/10] tun: Introduce virtio-net hash reporting feature

From: Akihiko Odaki
Date: Tue Oct 08 2024 - 03:57:55 EST

Allow the guest to reuse the hash value to make receive steering
consistent between the host and guest, and to save hash computation.

Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
---
Documentation/networking/tuntap.rst | 7 +++
drivers/net/Kconfig | 1 +
drivers/net/tap.c | 45 ++++++++++++++--
drivers/net/tun.c | 46 ++++++++++++----
drivers/net/tun_vnet.h | 102 +++++++++++++++++++++++++++++++-----
include/linux/if_tap.h | 2 +
include/uapi/linux/if_tun.h | 48 +++++++++++++++++
7 files changed, 223 insertions(+), 28 deletions(-)

diff --git a/Documentation/networking/tuntap.rst b/Documentation/networking/tuntap.rst
index 4d7087f727be..86b4ae8caa8a 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 9920b3a68ed1..e2a7bd703550 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 9a34ceed0c2c..5e2fbe63ca47 100644
--- a/drivers/net/tap.c
+++ b/drivers/net/tap.c
@@ -179,6 +179,16 @@ static void tap_put_queue(struct tap_queue *q)
sock_put(&q->sk);
}

+static struct virtio_net_hash *tap_add_hash(struct sk_buff *skb)
+{
+ return (struct virtio_net_hash *)skb->cb;
+}
+
+static const struct virtio_net_hash *tap_find_hash(const struct sk_buff *skb)
+{
+ return (const struct virtio_net_hash *)skb->cb;
+}
+
/*
* 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 +199,7 @@ 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
@@ -198,15 +209,32 @@ static struct tap_queue *tap_get_queue(struct tap_dev *tap,
int numvtaps = READ_ONCE(tap->numvtaps);
__u32 rxq;

+ *tap_add_hash(skb) = (struct virtio_net_hash) { .report = VIRTIO_NET_HASH_REPORT_NONE };
+
if (!numvtaps)
goto out;

if (numvtaps == 1)
goto single;

+ 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(&tap->vnet_hash, skb, &keys_basic, rxq, tap_add_hash);
queue = rcu_dereference(tap->taps[rxq % numvtaps]);
goto out;
}
@@ -713,15 +741,16 @@ 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 < 0)
goto done;

- ret = tun_vnet_hdr_put(vnet_hdr_len, iter, &vnet_hdr);
+ ret = tun_vnet_hdr_put(vnet_hdr_len, iter, &vnet_hdr, ret);
if (ret < 0)
goto done;
}
@@ -1025,7 +1054,13 @@ 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,
+ cmd, sp);
+ rtnl_unlock();
+ return ret;
}
}

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index dd8799d19518..27308417b834 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 vnet_hash;
struct ethtool_link_ksettings link_ksettings;
/* init args */
struct file *file;
@@ -451,6 +452,16 @@ 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
@@ -459,12 +470,17 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
*/
static u16 tun_automq_select_queue(struct tun_struct *tun, 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 +489,13 @@ 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(&tun->vnet_hash, skb, &keys_basic, skb->l4_hash ? skb->hash : txq,
+ tun_add_hash);
+
return txq;
}

@@ -1990,10 +2013,8 @@ static ssize_t tun_put_user_xdp(struct tun_struct *tun,
size_t total;

if (tun->flags & IFF_VNET_HDR) {
- struct virtio_net_hdr gso = { 0 };
-
vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);
- ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
+ ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, NULL, 0);
if (ret < 0)
return ret;
}
@@ -2018,7 +2039,6 @@ static ssize_t tun_put_user(struct tun_struct *tun,
int vlan_offset = 0;
int vlan_hlen = 0;
int vnet_hdr_sz = 0;
- int ret;

if (skb_vlan_tag_present(skb))
vlan_hlen = VLAN_HLEN;
@@ -2043,13 +2063,15 @@ 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;
+ int ret;

- 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 < 0)
goto done;

- ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso);
+ ret = tun_vnet_hdr_put(vnet_hdr_sz, iter, &gso, ret);
if (ret < 0)
goto done;
}
@@ -3055,9 +3077,10 @@ 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, cmd, argp);
goto unlock;
+ }

netif_info(tun, drv, tun->dev, "tun_chr_ioctl cmd %u\n", cmd);

@@ -3256,7 +3279,8 @@ 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, cmd, argp);
}

if (do_notify)
diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h
index c40bde0fdf8c..589a97dd7d02 100644
--- a/drivers/net/tun_vnet.h
+++ b/drivers/net/tun_vnet.h
@@ -6,6 +6,9 @@
#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 *);
+
static inline bool tun_vnet_legacy_is_little_endian(unsigned int flags)
{
return !(IS_ENABLED(CONFIG_TUN_VNET_CROSS_LE) && (flags & TUN_VNET_BE)) &&
@@ -59,18 +62,31 @@ static inline __virtio16 cpu_to_tun_vnet16(unsigned int flags, u16 val)
}

static inline long tun_vnet_ioctl(int *sz, unsigned int *flags,
- unsigned int cmd, int __user *sp)
+ struct tun_vnet_hash *hash, long fallback,
+ unsigned int cmd, void __user *argp)
{
+ static const struct tun_vnet_hash cap = {
+ .flags = TUN_VNET_HASH_REPORT,
+ .types = VIRTIO_NET_SUPPORTED_HASH_TYPES
+ };
+ struct tun_vnet_hash hash_buf;
+ int __user *sp = argp;
int s;

switch (cmd) {
case TUNGETVNETHDRSZ:
+ if (!sz)
+ return -EBADFD;
+
s = *sz;
if (put_user(s, sp))
return -EFAULT;
return 0;

case TUNSETVNETHDRSZ:
+ if (!sz)
+ return -EBADFD;
+
if (get_user(s, sp))
return -EFAULT;
if (s < (int)sizeof(struct virtio_net_hdr))
@@ -80,12 +96,18 @@ static inline long tun_vnet_ioctl(int *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)
@@ -95,16 +117,56 @@ static inline long tun_vnet_ioctl(int *sz, unsigned int *flags,
return 0;

case TUNGETVNETBE:
+ if (!flags)
+ return -EBADFD;
+
return tun_vnet_get_be(*flags, sp);

case TUNSETVNETBE:
+ if (!flags)
+ return -EBADFD;
+
return tun_vnet_set_be(flags, sp);

+ case TUNGETVNETHASHCAP:
+ return copy_to_user(argp, &cap, sizeof(cap)) ? -EFAULT : 0;
+
+ case TUNSETVNETHASH:
+ if (!hash)
+ return -EBADFD;
+
+ if (copy_from_user(&hash_buf, argp, sizeof(hash_buf)))
+ return -EFAULT;
+
+ *hash = hash_buf;
+ return 0;
+
default:
- return -EINVAL;
+ return fallback;
}
}

+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->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->types, keys),
+ .value = value
+ };
+}
+
static inline int tun_vnet_hdr_get(int sz, unsigned int flags,
struct iov_iter *from,
struct virtio_net_hdr *hdr)
@@ -130,15 +192,15 @@ 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 void *hdr, int content_sz)
{
if (iov_iter_count(iter) < sz)
return -EINVAL;

- if (copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr))
+ if (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;
@@ -151,32 +213,48 @@ static inline int tun_vnet_hdr_to_skb(unsigned int flags,
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);
+ int content_sz;
+
+ if (report) {
+ content_sz = sizeof(struct virtio_net_hdr_v1_hash);
+
+ *hdr = (struct virtio_net_hdr_v1_hash) {
+ .hdr = { .num_buffers = __cpu_to_virtio16(true, 1) },
+ .hash_value = cpu_to_le32(report->value),
+ .hash_report = cpu_to_le16(report->report)
+ };
+ } else {
+ content_sz = sizeof(struct virtio_net_hdr);
+ }

- 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;
}

- return 0;
+ return content_sz;
}

#endif /* TUN_VNET_H */
diff --git a/include/linux/if_tap.h b/include/linux/if_tap.h
index 553552fa635c..5bbb343a6dba 100644
--- a/include/linux/if_tap.h
+++ b/include/linux/if_tap.h
@@ -4,6 +4,7 @@

#include <net/sock.h>
#include <linux/skb_array.h>
+#include <uapi/linux/if_tun.h>

struct file;
struct socket;
@@ -43,6 +44,7 @@ struct tap_dev {
int numqueues;
netdev_features_t tap_features;
int minor;
+ struct tun_vnet_hash 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/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 287cdc81c939..d11e79b4e0dc 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -62,6 +62,34 @@
#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 %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 +143,24 @@ 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
+
+/**
+ * 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;
+};
+
#endif /* _UAPI__IF_TUN_H */

--
2.46.2