Re: [PATCH v6 1/6] virtio_net: Add functions for hashing

Willem de Bruijn
2025-01-09T14:13:35Z

Akihiko Odaki wrote:
> They are useful to implement VIRTIO_NET_F_RSS and
> VIRTIO_NET_F_HASH_REPORT.

Toeplitz potentially has users beyond virtio. I wonder if we should
from the start implement this as net/core/rss.c.

> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> include/linux/virtio_net.h | 188 +++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 188 insertions(+)
>
> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
> index 02a9f4dc594d..3b25ca75710b 100644
> --- a/include/linux/virtio_net.h
> +++ b/include/linux/virtio_net.h
> @@ -9,6 +9,194 @@
> #include <uapi/linux/tcp.h>
> #include <uapi/linux/virtio_net.h>
>
> +struct virtio_net_hash {
> + u32 value;
> + u16 report;
> +};
> +
> +struct virtio_net_toeplitz_state {
> + u32 hash;
> + const u32 *key;
> +};
> +
> +#define VIRTIO_NET_SUPPORTED_HASH_TYPES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 | \
> + VIRTIO_NET_RSS_HASH_TYPE_TCPv4 | \
> + VIRTIO_NET_RSS_HASH_TYPE_UDPv4 | \
> + VIRTIO_NET_RSS_HASH_TYPE_IPv6 | \
> + VIRTIO_NET_RSS_HASH_TYPE_TCPv6 | \
> + VIRTIO_NET_RSS_HASH_TYPE_UDPv6)
> +
> +#define VIRTIO_NET_RSS_MAX_KEY_SIZE 40
> +
> +static inline void virtio_net_toeplitz_convert_key(u32 *input, size_t len)
> +{
> + while (len >= sizeof(*input)) {
> + *input = be32_to_cpu((__force __be32)*input);
> + input++;
> + len -= sizeof(*input);
> + }
> +}
> +
> +static inline void virtio_net_toeplitz_calc(struct virtio_net_toeplitz_state *state,
> + const __be32 *input, size_t len)
> +{
> + while (len >= sizeof(*input)) {
> + for (u32 map = be32_to_cpu(*input); map; map &= (map - 1)) {
> + u32 i = ffs(map);
> +
> + state->hash ^= state->key[0] << (32 - i) |
> + (u32)((u64)state->key[1] >> i);
> + }
> +
> + state->key++;
> + input++;
> + len -= sizeof(*input);
> + }
> +}

Have you verified that this algorithm matches a known toeplitz
implementation. And computes the expected values for the test
inputs in

https://learn.microsoft.com/en-us/windows-hardware/drivers/network/verifying-the-rss-hash-calculation

We have a toeplitz implementation in
tools/testing/selftests/net/toeplitz.c that can also be used as
reference.

> +
> +static inline u8 virtio_net_hash_key_length(u32 types)
> +{
> + size_t len = 0;
> +
> + if (types & VIRTIO_NET_HASH_REPORT_IPv4)
> + len = max(len,
> + sizeof(struct flow_dissector_key_ipv4_addrs));
> +
> + if (types &
> + (VIRTIO_NET_HASH_REPORT_TCPv4 | VIRTIO_NET_HASH_REPORT_UDPv4))
> + len = max(len,
> + sizeof(struct flow_dissector_key_ipv4_addrs) +
> + sizeof(struct flow_dissector_key_ports));
> +
> + if (types & VIRTIO_NET_HASH_REPORT_IPv6)
> + len = max(len,
> + sizeof(struct flow_dissector_key_ipv6_addrs));
> +
> + if (types &
> + (VIRTIO_NET_HASH_REPORT_TCPv6 | VIRTIO_NET_HASH_REPORT_UDPv6))
> + len = max(len,
> + sizeof(struct flow_dissector_key_ipv6_addrs) +
> + sizeof(struct flow_dissector_key_ports));
> +
> + return len + 4;

Avoid magic constants. Please use sizeof or something else to signal
what this 4 derives from.