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@xxxxxxxxxx>
---
drivers/net/tun.c | 119
+++++++++++++++++++++++++++++++++++++++-----
include/uapi/linux/if_tun.h | 27 ++++++++++
2 files changed, 133 insertions(+), 13 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b8fcd71becac..5a429b391144 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -175,6 +175,9 @@ struct tun_prog {
struct tun_vnet_hash_container {
struct tun_vnet_hash common;
+ struct tun_vnet_hash_rss rss;
+ __be32 rss_key[VIRTIO_NET_RSS_MAX_KEY_SIZE];
+ u16 rss_indirection_table[];
};
/* Since the socket were moved to tun_file, to preserve the
behavior of persist
@@ -227,7 +230,7 @@ struct veth {
};
static const struct tun_vnet_hash tun_vnet_hash_cap = {
- .flags = TUN_VNET_HASH_REPORT,
+ .flags = TUN_VNET_HASH_REPORT | TUN_VNET_HASH_RSS,
.types = VIRTIO_NET_SUPPORTED_HASH_TYPES
};
@@ -591,6 +594,36 @@ static u16 tun_ebpf_select_queue(struct
tun_struct *tun, struct sk_buff *skb)
return ret % numqueues;
}
+static u16 tun_vnet_rss_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 virtio_net_hash hash;
+ u32 numqueues = READ_ONCE(tun->numqueues);
+ u16 txq, index;
+
+ if (!numqueues)
+ return 0;
+
+ if (!virtio_net_hash_rss(skb, vnet_hash->common.types,
vnet_hash->rss_key,
+ &hash))
+ return vnet_hash->rss.unclassified_queue % numqueues;
+
+ if (vnet_hash->common.flags & TUN_VNET_HASH_REPORT) {
+ ext = skb_ext_add(skb, SKB_EXT_TUN_VNET_HASH);
+ if (ext) {
+ ext->value = hash.value;
+ ext->report = hash.report;
+ }
+ }
+
+ index = hash.value & vnet_hash->rss.indirection_table_mask;
+ txq = READ_ONCE(vnet_hash->rss_indirection_table[index]);
+
+ return txq % numqueues;
+}
+
static u16 tun_select_queue(struct net_device *dev, struct sk_buff
*skb,
struct net_device *sb_dev)
{
@@ -603,7 +636,10 @@ static u16 tun_select_queue(struct net_device
*dev, struct sk_buff *skb,
} else {
struct tun_vnet_hash_container *vnet_hash =
rcu_dereference(tun->vnet_hash);
- ret = tun_automq_select_queue(tun, skb, vnet_hash);
+ if (vnet_hash && (vnet_hash->common.flags & TUN_VNET_HASH_RSS))
+ ret = tun_vnet_rss_select_queue(tun, skb, vnet_hash);
+ else
+ ret = tun_automq_select_queue(tun, skb, vnet_hash);
}
rcu_read_unlock();
@@ -3085,13 +3121,9 @@ 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;
@@ -3157,6 +3189,7 @@ static long __tun_chr_ioctl(struct file *file,
unsigned int cmd,
int ifindex;
int sndbuf;
int vnet_hdr_sz;
+ int fd;
int le;
int ret;
bool do_notify = false;
@@ -3460,11 +3493,27 @@ 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(fd, (int __user *)argp)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ vnet_hash = rtnl_dereference(tun->vnet_hash);
+ if (fd != -1 && vnet_hash && (vnet_hash->common.flags &
TUN_VNET_HASH_RSS)) {
+ ret = -EBUSY;
+ break;
+ }
+
+ ret = tun_set_ebpf(tun, &tun->steering_prog, fd);
break;
case TUNSETFILTEREBPF:
- ret = tun_set_ebpf(tun, &tun->filter_prog, argp);
+ if (get_user(fd, (int __user *)argp)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ ret = tun_set_ebpf(tun, &tun->filter_prog, fd);
break;
case TUNSETCARRIER:
@@ -3496,10 +3545,54 @@ static long __tun_chr_ioctl(struct file
*file, unsigned int cmd,
break;
}
- vnet_hash = kmalloc(sizeof(vnet_hash->common), GFP_KERNEL);
- if (!vnet_hash) {
- ret = -ENOMEM;
- break;
+ if (vnet_hash_common.flags & TUN_VNET_HASH_RSS) {
+ struct tun_vnet_hash_rss rss;
+ size_t indirection_table_size;
+ size_t key_size;
+ size_t size;
+
+ if (tun->steering_prog) {
+ ret = -EBUSY;
+ break;
+ }
+
+ if (copy_from_user(&rss, argp, sizeof(rss))) {
+ ret = -EFAULT;
+ break;
+ }
+ argp = (struct tun_vnet_hash_rss __user *)argp + 1;
+
+ indirection_table_size =
((size_t)rss.indirection_table_mask + 1) * 2;
