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.
Extend the steering program feature by introducing a dedicated program type: BPF_PROG_TYPE_VNET_HASH. This program type is capable to report the hash value and the queue to use at the same time.
This is a rewrite of a RFC patch series submitted by Yuri Benditovich that incorporates feedbacks for the series and V1 of this series: https://lore.kernel.org/lkml/20210112194143.1494-1-yuri.benditovich@daynix.c...
QEMU patched to use this new feature is available at: https://github.com/daynix/qemu/tree/akihikodaki/bpf
The QEMU patches will soon be submitted to the upstream as RFC too.
V1 -> V2: Changed to introduce a new BPF program type.
Akihiko Odaki (7): bpf: Introduce BPF_PROG_TYPE_VNET_HASH bpf: Add vnet_hash members to __sk_buff skbuff: Introduce SKB_EXT_TUN_VNET_HASH virtio_net: Add virtio_net_hdr_v1_hash_from_skb() tun: Support BPF_PROG_TYPE_VNET_HASH selftests/bpf: Test BPF_PROG_TYPE_VNET_HASH vhost_net: Support VIRTIO_NET_F_HASH_REPORT
Documentation/bpf/bpf_prog_run.rst | 1 + Documentation/bpf/libbpf/program_types.rst | 2 + drivers/net/tun.c | 158 +++++-- drivers/vhost/net.c | 16 +- include/linux/bpf_types.h | 2 + include/linux/filter.h | 7 + include/linux/skbuff.h | 10 + include/linux/virtio_net.h | 22 + include/uapi/linux/bpf.h | 5 + kernel/bpf/verifier.c | 6 + net/core/filter.c | 86 +++- net/core/skbuff.c | 3 + tools/include/uapi/linux/bpf.h | 5 + tools/lib/bpf/libbpf.c | 2 + tools/testing/selftests/bpf/config | 1 + tools/testing/selftests/bpf/config.aarch64 | 1 - .../selftests/bpf/prog_tests/vnet_hash.c | 385 ++++++++++++++++++ tools/testing/selftests/bpf/progs/vnet_hash.c | 16 + 18 files changed, 681 insertions(+), 47 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/vnet_hash.c create mode 100644 tools/testing/selftests/bpf/progs/vnet_hash.c