On 2023/10/09 20:38, Michael S. Tsirkin wrote:

Akihiko Odaki sorry about reposts. Having an email with two "@" in the CC list: xuanzhuo@linux.alibaba.comshuah@kernel.org tripped up mutt's reply-all for me and made it send to you only.

I am guessing you meant two addresses: xuanzhuo@linux.alibaba.com and shuah@kernel.org.

Oops, I'll send the future versions with corrected addresses (and fewer CCs).

On Sun, Oct 08, 2023 at 02:20:49PM +0900, Akihiko Odaki wrote:

...

virtio-net have two usage of hashes: one is RSS and another is hash reporting. 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.

Introduce the code to compute hashes 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 it makes little sense to allow to implement different hashing algorithms with eBPF since the hash value reported by virtio-net is strictly defined by the specification.

The hash value already stored in sk_buff is not used and computed independently since it may have been computed in a way not conformant with the specification.

Signed-off-by: Akihiko Odaki akihiko.odaki@daynix.com

drivers/net/tun.c | 187 ++++++++++++++++++++++++++++++++---- include/uapi/linux/if_tun.h | 16 +++ 2 files changed, 182 insertions(+), 21 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 89ab9efe522c..561a573cd008 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -171,6 +171,9 @@ struct tun_prog { struct bpf_prog *prog; }; +#define TUN_VNET_HASH_MAX_KEY_SIZE 40 +#define TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH 128

where do these come from?

TUN_VNET_HASH_MAX_KEY_SIZE is the total size of IPv6 addresses and TCP/UDP ports.

TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH is from the following statement in VIRTIO Version 1.2 clause 5.1.4.1:

The device MUST set rss_max_indirection_table_length to at least 128, if it offers VIRTIO_NET_F_RSS.

...

/* 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.

@@ -209,6 +212,9 @@ struct tun_struct { struct tun_prog __rcu *steering_prog; struct tun_prog __rcu *filter_prog; struct ethtool_link_ksettings link_ksettings;

• struct tun_vnet_hash vnet_hash;
• u16 vnet_hash_indirection_table[TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH];
• u32 vnet_hash_key[TUN_VNET_HASH_MAX_KEY_SIZE / 4];

That's quite a lot of data to add in this struct, and will be used by a small minority of users. Are you pushing any hot data out of cache with this? Why not allocate these as needed?

I put this here just because it's convenient. It would be better to have a separate structure.

...

/* init args */ struct file *file; struct ifreq *ifr; @@ -219,6 +225,13 @@ struct veth { __be16 h_vlan_TCI; }; +static const struct tun_vnet_hash_cap tun_vnet_hash_cap = {

• .max_indirection_table_length =

• TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH,
  

• .types = VIRTIO_NET_SUPPORTED_HASH_TYPES

+};

• static void tun_flow_init(struct tun_struct *tun); static void tun_flow_uninit(struct tun_struct *tun);

@@ -320,10 +333,16 @@ static long tun_set_vnet_be(struct tun_struct *tun, int __user *argp) if (get_user(be, argp)) return -EFAULT;

• if (be)

• if (be) {

• if (!(tun->flags & TUN_VNET_LE) &&
  

•     (tun->vnet_hash.flags & TUN_VNET_HASH_REPORT)) {
  

• 	return -EINVAL;
  

• }
  

• tun->flags |= TUN_VNET_BE;

• else

• } else { tun->flags &= ~TUN_VNET_BE;
• }

return 0; } @@ -558,15 +577,47 @@ static u16 tun_ebpf_select_queue(struct tun_struct *tun, struct sk_buff *skb) return ret % numqueues; } +static u16 tun_vnet_select_queue(struct tun_struct *tun, struct sk_buff *skb) +{

• u32 value = qdisc_skb_cb(skb)->tun_vnet_hash_value;
• u32 numqueues;
• u32 index;
• u16 queue;
• numqueues = READ_ONCE(tun->numqueues);
• if (!numqueues)

• return 0;
  

• index = value & READ_ONCE(tun->vnet_hash.indirection_table_mask);
• queue = READ_ONCE(tun->vnet_hash_indirection_table[index]);
• if (!queue)

• queue = READ_ONCE(tun->vnet_hash.unclassified_queue);
  

Apparently 0 is an illegal queue value? You are making this part of UAPI better document things like this.

Well, I don't think so. I naively copied this from QEMU's eBPF steering program but I think this should check tun_vnet_hash_report == VIRTIO_NET_HASH_REPORT_NONE. I'll fix it.

...

• return queue % numqueues;

+}

• static u16 tun_select_queue(struct net_device *dev, struct sk_buff *skb, struct net_device *sb_dev) { struct tun_struct *tun = netdev_priv(dev);
• u8 vnet_hash_flags = READ_ONCE(tun->vnet_hash.flags);
• struct virtio_net_hash hash; u16 ret;

• if (vnet_hash_flags & (TUN_VNET_HASH_RSS | TUN_VNET_HASH_REPORT)) {

• virtio_net_hash(skb, READ_ONCE(tun->vnet_hash.types),
  

• 		tun->vnet_hash_key, &hash);
  

What are all these READ_ONCE things doing? E.g. you seem to be very content to have tun->vnet_hash.types read twice apparently? This is volatile which basically breaks all compiler's attempts to optimize code - needs to be used judiciously.

I'll replace them with one RCU dereference once I extract them into a structure.

...

• skb->tun_vnet_hash = true;
  

• qdisc_skb_cb(skb)->tun_vnet_hash_value = hash.value;
  

• qdisc_skb_cb(skb)->tun_vnet_hash_report = hash.report;
  

• }
• rcu_read_lock(); if (rcu_dereference(tun->steering_prog)) ret = tun_ebpf_select_queue(tun, skb);
• else if (vnet_hash_flags & TUN_VNET_HASH_RSS)

• ret = tun_vnet_select_queue(tun, skb);
  

  else ret = tun_automq_select_queue(tun, skb); rcu_read_unlock();

@@ -2088,10 +2139,15 @@ static ssize_t tun_put_user(struct tun_struct *tun, struct iov_iter *iter) { struct tun_pi pi = { 0, skb->protocol };

• struct virtio_net_hash vnet_hash = {

• .value = qdisc_skb_cb(skb)->tun_vnet_hash_value,
  

• .report = qdisc_skb_cb(skb)->tun_vnet_hash_report
  

• }; ssize_t total; int vlan_offset = 0; int vlan_hlen = 0; int vnet_hdr_sz = 0;
• size_t vnet_hdr_content_sz;

if (skb_vlan_tag_present(skb)) vlan_hlen = VLAN_HLEN; @@ -2116,31 +2172,49 @@ static ssize_t tun_put_user(struct tun_struct *tun, } if (vnet_hdr_sz) {

• struct virtio_net_hdr gso;
  

• union {
  

• 	struct virtio_net_hdr hdr;
  

• 	struct virtio_net_hdr_v1_hash v1_hash_hdr;
  

• } 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)) {
  

• if ((READ_ONCE(tun->vnet_hash.flags) & TUN_VNET_HASH_REPORT) &&
  

•     vnet_hdr_sz >= sizeof(hdr.v1_hash_hdr) &&
  

•     skb->tun_vnet_hash) {
  

• 	vnet_hdr_content_sz = sizeof(hdr.v1_hash_hdr);
  

• 	ret = virtio_net_hdr_v1_hash_from_skb(skb,
  

• 					      &hdr.v1_hash_hdr,
  

• 					      true,
  

• 					      vlan_hlen,
  

• 					      &vnet_hash);
  

• } else {
  

• 	vnet_hdr_content_sz = sizeof(hdr.hdr);
  

• 	ret = virtio_net_hdr_from_skb(skb, &hdr.hdr,
  

• 				      tun_is_little_endian(tun),
  

• 				      true, vlan_hlen);
  

• }
  

• if (ret) {
  struct skb_shared_info *sinfo = skb_shinfo(skb);
  pr_err("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, hdr.hdr.gso_size),
  

• 	       tun16_to_cpu(tun, 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((int)tun16_to_cpu(tun, 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(&hdr, vnet_hdr_content_sz, iter) != vnet_hdr_content_sz)
  return -EFAULT;
  

• iov_iter_advance(iter, vnet_hdr_sz - sizeof(gso));
  

• iov_iter_advance(iter, vnet_hdr_sz - vnet_hdr_content_sz);
  

  }

if (vlan_hlen) { @@ -3007,24 +3081,27 @@ static int tun_set_queue(struct file *file, struct ifreq *ifr) return ret; } -static int tun_set_ebpf(struct tun_struct *tun, struct tun_prog __rcu **prog_p,

• 	void __user *data)
  

+static struct bpf_prog *tun_set_ebpf(struct tun_struct *tun,

• 		     struct tun_prog __rcu **prog_p,
  

• 		     void __user *data)
  

  { struct bpf_prog *prog; int fd;
• int ret;

if (copy_from_user(&fd, data, sizeof(fd)))

• return -EFAULT;
  

• return ERR_PTR(-EFAULT);
  

if (fd == -1) { prog = NULL; } else { prog = bpf_prog_get_type(fd, BPF_PROG_TYPE_SOCKET_FILTER); if (IS_ERR(prog))

• 	return PTR_ERR(prog);
  

• 	return prog;
  

  }

• return __tun_set_ebpf(tun, prog_p, prog);

• ret = __tun_set_ebpf(tun, prog_p, prog);
• return ret ? ERR_PTR(ret) : prog; }

/* Return correct value for tun->dev->addr_len based on tun->dev->type. */ @@ -3082,6 +3159,11 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, int le; int ret; bool do_notify = false;

• struct bpf_prog *bpf_ret;
• struct tun_vnet_hash vnet_hash;
• u16 vnet_hash_indirection_table[TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH];
• u8 vnet_hash_key[TUN_VNET_HASH_MAX_KEY_SIZE];
• size_t len;

if (cmd == TUNSETIFF || cmd == TUNSETQUEUE || (_IOC_TYPE(cmd) == SOCK_IOC_TYPE && cmd != SIOCGSKNS)) { @@ -3295,7 +3377,10 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, ret = -EFAULT; break; }

• if (vnet_hdr_sz < (int)sizeof(struct virtio_net_hdr)) {
  

• if (vnet_hdr_sz <
  

•     (int)((tun->vnet_hash.flags & TUN_VNET_HASH_REPORT) ?
  

• 	  sizeof(struct virtio_net_hdr_v1_hash) :
  

• 	  sizeof(struct virtio_net_hdr))) {
  ret = -EINVAL;
  break;
  

  }

@@ -3314,10 +3399,16 @@ 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 {
  

• 	if (!tun_legacy_is_little_endian(tun)) {
  

• 		ret = -EINVAL;
  

• 		break;
  

• 	}
  

• tun->flags &= ~TUN_VNET_LE;
  

• }
  

  break;

case TUNGETVNETBE: @@ -3360,11 +3451,17 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, break; case TUNSETSTEERINGEBPF:

• ret = tun_set_ebpf(tun, &tun->steering_prog, argp);
  

• bpf_ret = tun_set_ebpf(tun, &tun->steering_prog, argp);
  

• if (IS_ERR(bpf_ret))
  

• 	ret = PTR_ERR(bpf_ret);
  

• else if (bpf_ret)
  

• 	tun->vnet_hash.flags &= ~TUN_VNET_HASH_RSS;
  

what is this doing?

It's unsetting RSS because steering eBPF is incompatible with RSS. Willem proposed to return EBUSY instead so I'll do so in the future.

...

break;

case TUNSETFILTEREBPF:

• ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
  

• bpf_ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
  

• if (IS_ERR(bpf_ret))
  

• 	ret = PTR_ERR(bpf_ret);
  

  break;

case TUNSETCARRIER: @@ -3382,6 +3479,54 @@ static long __tun_chr_ioctl(struct file *file, unsigned int cmd, ret = open_related_ns(&net->ns, get_net_ns); break;

• case TUNGETVNETHASHCAP:

• if (copy_to_user(argp, &tun_vnet_hash_cap,
  

• 		 sizeof(tun_vnet_hash_cap)))
  

• 	ret = -EFAULT;
  

• break;
  

• case TUNSETVNETHASH:

• len = sizeof(vnet_hash);
  

• if (copy_from_user(&vnet_hash, argp, len)) {
  

• 	ret = -EFAULT;
  

• 	break;
  

• }
  

what if flags has some bits set you don't know how to handle? should these be ignored as now or cause a failure? these decisions all affect uapi.

Currently they are ignored.

...

• if (((vnet_hash.flags & TUN_VNET_HASH_REPORT) &&
  

•      (tun->vnet_hdr_sz < sizeof(struct virtio_net_hdr_v1_hash) ||
  

•       !tun_is_little_endian(tun))) ||
  

•      vnet_hash.indirection_table_mask >=
  

•      TUN_VNET_HASH_MAX_INDIRECTION_TABLE_LENGTH) {
  

• 	ret = -EINVAL;
  

• 	break;
  

• }
  

Given this is later used to index within an array one has to be very careful about spectre things here, which this code isn't.

I have totally forgotten that. Thanks for pointing this out.

...

• argp = (u8 __user *)argp + len;
  

• len = (vnet_hash.indirection_table_mask + 1) * 2;
  

comment pointer math tricks like this extensively please.

Ok, I will.

...

• if (copy_from_user(vnet_hash_indirection_table, argp, len)) {
  

• 	ret = -EFAULT;
  

• 	break;
  

• }
  

• argp = (u8 __user *)argp + len;
  

• len = virtio_net_hash_key_length(vnet_hash.types);
  

• if (copy_from_user(vnet_hash_key, argp, len)) {
  

• 	ret = -EFAULT;
  

• 	break;
  

• }
  

• tun->vnet_hash = vnet_hash;
  

• memcpy(tun->vnet_hash_indirection_table,
  

•        vnet_hash_indirection_table,
  

•        (vnet_hash.indirection_table_mask + 1) * 2);
  

• memcpy(tun->vnet_hash_key, vnet_hash_key, len);
  

• if (vnet_hash.flags & TUN_VNET_HASH_RSS)
  

• 	__tun_set_ebpf(tun, &tun->steering_prog, NULL);
  

• break;
  

• default: ret = -EINVAL; break;

diff --git a/include/uapi/linux/if_tun.h b/include/uapi/linux/if_tun.h index 287cdc81c939..dc591cd897c8 100644 --- a/include/uapi/linux/if_tun.h +++ b/include/uapi/linux/if_tun.h @@ -61,6 +61,8 @@ #define TUNSETFILTEREBPF _IOR('T', 225, int) #define TUNSETCARRIER _IOW('T', 226, int) #define TUNGETDEVNETNS _IO('T', 227) +#define TUNGETVNETHASHCAP _IO('T', 228) +#define TUNSETVNETHASH _IOW('T', 229, unsigned int) /* TUNSETIFF ifr flags */ #define IFF_TUN 0x0001 @@ -115,4 +117,18 @@ struct tun_filter { __u8 addr[][ETH_ALEN]; }; +struct tun_vnet_hash_cap {

• __u16 max_indirection_table_length;
• __u32 types;

+};

There's hidden padding in this struct - not good, copy will leak kernel info out.

I'll add an explicit padding.

...

+#define TUN_VNET_HASH_RSS 0x01 +#define TUN_VNET_HASH_REPORT 0x02

Do you intend to add more flags down the road? How will userspace know what is supported?

I don't intend to do so, but perhaps it may be better to return EINVAL when an unknown flag is set.

...

+struct tun_vnet_hash {

• __u8 flags;
• __u32 types;
• __u16 indirection_table_mask;
• __u16 unclassified_queue;

+};

Padding here too. Best avoided.

Perhaps it may be easier just to grow flags into u32.

In any case, document UAPI please.

Sure, I'll.