Willem de Bruijn
2023-Oct-09 08:13 UTC
[RFC PATCH 5/7] tun: Introduce virtio-net hashing feature
On Sun, Oct 8, 2023 at 12:22?AM Akihiko Odaki <akihiko.odaki at daynix.com> 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 at daynix.com>> @@ -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) {Isn't vnet_hdr_sz guaranteed to be >= hdr.v1_hash_hdr, by virtue of the set hash ioctl failing otherwise? Such checks should be limited to control path where possible> + 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); > + } > +