On Mon, Oct 9, 2023 at 3:44 AM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> wrote: > > On 2023/10/09 17:13, Willem de Bruijn wrote: > > On Sun, Oct 8, 2023 at 12:22 AM Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> 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@xxxxxxxxxx> > > > >> @@ -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 > > There is a potential race since tun->vnet_hash.flags and vnet_hdr_sz are > not read at once. It should not be possible to downgrade the hdr_sz once v1 is selected. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization