On 2023/10/09 18:54, Willem de Bruijn wrote:
On Mon, Oct 9, 2023 at 3:44 AM Akihiko Odaki akihiko.odaki@daynix.com wrote:
On 2023/10/09 17:13, Willem de Bruijn wrote:
On Sun, Oct 8, 2023 at 12:22 AM Akihiko Odaki akihiko.odaki@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@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
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.
I see nothing that prevents shrinking the header size.
tun->vnet_hash.flags is read after vnet_hdr_sz so the race can happen even for the case the header size grows though this can be fixed by reordering the two reads.