Re: [PATCH RFC v3 6/9] tun: Introduce virtio-net hash reporting feature

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On 2024/09/18 15:17, Willem de Bruijn wrote:
Akihiko Odaki wrote:
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/tun.c                   | 146 +++++++++++++++++++++++++++++++-----
  include/uapi/linux/if_tun.h         |  44 +++++++++++
  4 files changed, 180 insertions(+), 18 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/tun.c b/drivers/net/tun.c
index 9d93ab9ee58f..b8fcd71becac 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -173,6 +173,10 @@ struct tun_prog {
  	struct bpf_prog *prog;
  };
+struct tun_vnet_hash_container {
+	struct tun_vnet_hash common;
+};
+
  /* Since the socket were moved to tun_file, to preserve the behavior of persist
   * device, socket filter, sndbuf and vnet header size were restore when the
   * file were attached to a persist device.
@@ -210,6 +214,7 @@ 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;

This is just

+struct tun_vnet_hash {
+       u32 value;
+       u16 report;
+};

Can just be fields in the struct directly.

I will change to store struct tun_vnet_hash directly.


Also, only one bit really used for report, so probably can be
condensed further.

It is more than one bit; the report types are defined as follows:
#define VIRTIO_NET_HASH_REPORT_NONE            0
#define VIRTIO_NET_HASH_REPORT_IPv4            1
#define VIRTIO_NET_HASH_REPORT_TCPv4           2
#define VIRTIO_NET_HASH_REPORT_UDPv4           3
#define VIRTIO_NET_HASH_REPORT_IPv6            4
#define VIRTIO_NET_HASH_REPORT_TCPv6           5
#define VIRTIO_NET_HASH_REPORT_UDPv6           6
#define VIRTIO_NET_HASH_REPORT_IPv6_EX         7
#define VIRTIO_NET_HASH_REPORT_TCPv6_EX        8
#define VIRTIO_NET_HASH_REPORT_UDPv6_EX        9


  	struct ethtool_link_ksettings link_ksettings;
  	/* init args */
  	struct file *file;
@@ -221,6 +226,11 @@ struct veth {
  	__be16 h_vlan_TCI;
  };
+static const struct tun_vnet_hash tun_vnet_hash_cap = {
+	.flags = TUN_VNET_HASH_REPORT,
+	.types = VIRTIO_NET_SUPPORTED_HASH_TYPES
+};
+
  static void tun_flow_init(struct tun_struct *tun);
  static void tun_flow_uninit(struct tun_struct *tun);
@@ -322,10 +332,17 @@ static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp)
  	if (get_user(be, argp))
  		return -EFAULT;
- if (be)
+	if (be) {
+		struct tun_vnet_hash_container *vnet_hash = rtnl_dereference(tun->vnet_hash);
+
+		if (!(tun->flags & TUN_VNET_LE) &&
+		    vnet_hash && (vnet_hash->flags & TUN_VNET_HASH_REPORT))
+			return -EBUSY;
+

Doesn't be here imply !tun->flags & TUN_VNET_LE? Same again below.

Unfortunately no. TUN_VNET_LE and TUN_VNET_BE can be set at the same time, and TUN_VNET_LE is enforced in such a case.


  		tun->flags |= TUN_VNET_BE;
-	else
+	} else {
  		tun->flags &= ~TUN_VNET_BE;
+	}
return 0;
  }
@@ -522,14 +539,20 @@ static inline void tun_flow_save_rps_rxhash(struct tun_flow_entry *e, u32 hash)
   * 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, struct sk_buff *skb,
+				   const struct tun_vnet_hash_container *vnet_hash)
  {
+	struct tun_vnet_hash_ext *ext;
+	struct flow_keys keys;
  	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);
@@ -538,6 +561,16 @@ static u16 tun_automq_select_queue(struct tun_struct *tun, struct sk_buff *skb)
  		txq = reciprocal_scale(txq, numqueues);
  	}
+ if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_REPORT)) {
+		ext = skb_ext_add(skb, SKB_EXT_TUN_VNET_HASH);
+		if (ext) {
+			u32 types = vnet_hash->common.types;
+
+			ext->report = virtio_net_hash_report(types, keys.basic);
+			ext->value = skb->l4_hash ? skb->hash : txq;
+		}
+	}
+
  	return txq;
  }
@@ -565,10 +598,13 @@ 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);
+
+		ret = tun_automq_select_queue(tun, skb, vnet_hash);

Already passing tun, no need to pass tun->vnet_hash separately.

I will remove the parameter with v4.

+	}
  	rcu_read_unlock();
return ret;
@@ -2120,33 +2156,63 @@ static ssize_t tun_put_user(struct tun_struct *tun,
  	}
if (vnet_hdr_sz) {
-		struct virtio_net_hdr gso;
+		struct tun_vnet_hash_ext *ext;
+		size_t vnet_hdr_content_sz = sizeof(struct virtio_net_hdr);
+		union {
+			struct virtio_net_hdr hdr;
+			struct virtio_net_hdr_v1_hash hdr_v1_hash;
+		} vnet_hdr;
+		int ret;
if (iov_iter_count(iter) < vnet_hdr_sz)
  			return -EINVAL;
- if (virtio_net_hdr_from_skb(skb, &gso,
-					    tun_is_little_endian(tun), true,
-					    vlan_hlen)) {
+		ext = vnet_hdr_sz < sizeof(vnet_hdr.hdr_v1_hash) ?
+		      NULL : skb_ext_find(skb, SKB_EXT_TUN_VNET_HASH);
+
+		if (ext) {
+			struct virtio_net_hash hash = {
+				.value = ext->value,
+				.report = ext->report,
+			};
+
+			vnet_hdr_content_sz = sizeof(vnet_hdr.hdr_v1_hash);
+			ret = virtio_net_hdr_v1_hash_from_skb(skb,
+							      &vnet_hdr.hdr_v1_hash,
+							      true,
+							      vlan_hlen,
+							      &hash);
+		} else {
+			vnet_hdr_content_sz = sizeof(struct virtio_net_hdr);
+			ret = virtio_net_hdr_from_skb(skb,
+						      &vnet_hdr.hdr,
+						      tun_is_little_endian(tun),
+						      true,
+						      vlan_hlen);
+		}
+

This is why just setting the fields directly rather than adding
virtio_net_hdr_v1_hash_from_skb is actually simpler.

I'll make a change accordingly in v4.


+		if (ret) {
  			struct skb_shared_info *sinfo = skb_shinfo(skb);
if (net_ratelimit()) {
  				netdev_err(tun->dev, "unexpected GSO type: 0x%x, gso_size %d, hdr_len %d\n",
-					   sinfo->gso_type, tun16_to_cpu(tun, gso.gso_size),
-					   tun16_to_cpu(tun, gso.hdr_len));
+					   sinfo->gso_type,
+					   tun16_to_cpu(tun, vnet_hdr.hdr.gso_size),
+					   tun16_to_cpu(tun, vnet_hdr.hdr.hdr_len));
  				print_hex_dump(KERN_ERR, "tun: ",
  					       DUMP_PREFIX_NONE,
  					       16, 1, skb->head,
-					       min((int)tun16_to_cpu(tun, gso.hdr_len), 64), true);
+					       min(tun16_to_cpu(tun, vnet_hdr.hdr.hdr_len), 64),
+					       true);
  			}
  			WARN_ON_ONCE(1);
  			return -EINVAL;
  		}
- if (copy_to_iter(&gso, sizeof(gso), iter) != sizeof(gso))
+		if (copy_to_iter(&vnet_hdr, vnet_hdr_content_sz, iter) != vnet_hdr_content_sz)
  			return -EFAULT;
- iov_iter_zero(vnet_hdr_sz - sizeof(gso), iter);
+		iov_iter_zero(vnet_hdr_sz - vnet_hdr_content_sz, iter);
  	}
if (vlan_hlen) {
@@ -3094,6 +3160,8 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  	int le;
  	int ret;
  	bool do_notify = false;
+	struct tun_vnet_hash vnet_hash_common;
+	struct tun_vnet_hash_container *vnet_hash;
if (cmd == TUNSETIFF || cmd == TUNSETQUEUE ||
  	    (_IOC_TYPE(cmd) == SOCK_IOC_TYPE && cmd != SIOCGSKNS)) {
@@ -3115,6 +3183,9 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  		if (!ns_capable(net->user_ns, CAP_NET_ADMIN))
  			return -EPERM;
  		return open_related_ns(&net->ns, get_net_ns);
+	} else if (cmd == TUNGETVNETHASHCAP) {
+		return copy_to_user(argp, &tun_vnet_hash_cap, sizeof(tun_vnet_hash_cap)) ?
+		       -EFAULT : 0;
  	}
rtnl_lock();
@@ -3314,6 +3385,13 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  			break;
  		}
+ vnet_hash = rtnl_dereference(tun->vnet_hash);
+		if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_REPORT) &&
+		    vnet_hdr_sz < (int)sizeof(struct virtio_net_hdr_v1_hash)) {
+			ret = -EBUSY;
+			break;
+		}
+
  		tun->vnet_hdr_sz = vnet_hdr_sz;
  		break;
@@ -3328,10 +3406,18 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  			ret = -EFAULT;
  			break;
  		}
-		if (le)
+		if (le) {
  			tun->flags |= TUN_VNET_LE;
-		else
+		} else {
+			vnet_hash = rtnl_dereference(tun->vnet_hash);
+			if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_REPORT) &&
+			    !tun_legacy_is_little_endian(tun)) {
+				ret = -EBUSY;
+				break;
+			}
+
  			tun->flags &= ~TUN_VNET_LE;
+		}
  		break;
case TUNGETVNETBE:
@@ -3396,6 +3482,30 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd,
  		ret = open_related_ns(&net->ns, get_net_ns);
  		break;
+ case TUNSETVNETHASH:
+		if (copy_from_user(&vnet_hash_common, argp, sizeof(vnet_hash_common))) {
+			ret = -EFAULT;
+			break;
+		}
+		argp = (struct tun_vnet_hash __user *)argp + 1;
+
+		if ((vnet_hash_common.flags & TUN_VNET_HASH_REPORT) &&
+		    (tun->vnet_hdr_sz < sizeof(struct virtio_net_hdr_v1_hash) ||
+		     !tun_is_little_endian(tun))) {
+			ret = -EBUSY;
+			break;
+		}
+
+		vnet_hash = kmalloc(sizeof(vnet_hash->common), GFP_KERNEL);
+		if (!vnet_hash) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		vnet_hash->common = vnet_hash_common;
+		kfree_rcu_mightsleep(rcu_replace_pointer_rtnl(tun->vnet_hash, vnet_hash));
+		break;
+
  	default:
  		ret = -EINVAL;
  		break;
diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h
index 287cdc81c939..1561e8ce0a0a 100644
--- a/include/uapi/linux/if_tun.h
+++ b/include/uapi/linux/if_tun.h
@@ -62,6 +62,30 @@
  #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.
+ *
+ * %TUNSETVNETHDRSZ ioctl must be called with a number greater than or equal to
+ * the size of &struct virtio_net_hdr_v1_hash before calling this ioctl with
+ * %TUN_VNET_HASH_REPORT.
+ *
+ * The virtio_net header must be configured as little-endian before calling this
+ * ioctl with %TUN_VNET_HASH_REPORT.
+ *
+ * This ioctl currently has no effect on XDP packets.
+ */
+#define TUNSETVNETHASH _IOW('T', 229, struct tun_vnet_hash)
+
  /* TUNSETIFF ifr flags */
  #define IFF_TUN		0x0001
  #define IFF_TAP		0x0002
@@ -115,4 +139,24 @@ 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;
+};
+

The values for flags and types should probably be defined here.

I put TUN_VNET_HASH_REPORT before struct tun_vnet_hash following the examples of TUN_PKT_STRIP/struct tun_pi and TUN_FLT_ALLMULTI/struct tun_filter. The types are defined in: include/uapi/linux/virtio_net.h

Regards,
Akihiko Odaki


  #endif /* _UAPI__IF_TUN_H */

--
2.46.0







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