Re: [PATCH bpf RFC-V3 1/5] xdp: rss hash types representation

Stanislav Fomichev
2023-03-30T18:35:43Z

On 03/30, Jesper Dangaard Brouer wrote:
> The RSS hash type specifies what portion of packet data NIC hardware used
> when calculating RSS hash value. The RSS types are focused on Internet
> traffic protocols at OSI layers L3 and L4. L2 (e.g. ARP) often get hash
> value zero and no RSS type. For L3 focused on IPv4 vs. IPv6, and L4
> primarily TCP vs UDP, but some hardware supports SCTP.

> Hardware RSS types are differently encoded for each hardware NIC. Most
> hardware represent RSS hash type as a number. Determining L3 vs L4 often
> requires a mapping table as there often isn't a pattern or sorting
> according to ISO layer.

> The patch introduce a XDP RSS hash type (enum xdp_rss_hash_type) that
> contain combinations to be used by drivers, which gets build up with bits
> from enum xdp_rss_type_bits. Both enum xdp_rss_type_bits and
> xdp_rss_hash_type get exposed to BPF via BTF, and it is up to the
> BPF-programmer to match using these defines.

> This proposal change the kfunc API bpf_xdp_metadata_rx_hash() adding
> a pointer value argument for provide the RSS hash type.

> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
> include/linux/netdevice.h | 3 ++-
> include/net/xdp.h | 46
> +++++++++++++++++++++++++++++++++++++++++++++
> net/core/xdp.c | 10 +++++++++-
> 3 files changed, 57 insertions(+), 2 deletions(-)

> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 470085b121d3..c35f04f636f1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1624,7 +1624,8 @@ struct net_device_ops {

> struct xdp_metadata_ops {
> int (*xmo_rx_timestamp)(const struct xdp_md *ctx, u64 *timestamp);
> - int (*xmo_rx_hash)(const struct xdp_md *ctx, u32 *hash);
> + int (*xmo_rx_hash)(const struct xdp_md *ctx, u32 *hash,
> + enum xdp_rss_hash_type *rss_type);
> };

> /**
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 41c57b8b1671..130091a55a6f 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -8,6 +8,7 @@

> #include <linux/skbuff.h> /* skb_shared_info */
> #include <uapi/linux/netdev.h>
> +#include <linux/bitfield.h>

> /**
> * DOC: XDP RX-queue information
> @@ -425,6 +426,51 @@ XDP_METADATA_KFUNC_xxx
> MAX_XDP_METADATA_KFUNC,
> };

> +enum xdp_rss_type_bits {
> + XDP_RSS_L3_IPV4 = BIT(0),
> + XDP_RSS_L3_IPV6 = BIT(1),
> +
> + /* The fixed (L3) IPv4 and IPv6 headers can both be followed by
> + * variable/dynamic headers, IPv4 called Options and IPv6 called
> + * Extension Headers. HW RSS type can contain this info.
> + */
> + XDP_RSS_L3_DYNHDR = BIT(2),
> +
> + /* When RSS hash covers L4 then drivers MUST set XDP_RSS_L4 bit in
> + * addition to the protocol specific bit. This ease interaction with
> + * SKBs and avoids reserving a fixed mask for future L4 protocol bits.
> + */
> + XDP_RSS_L4 = BIT(3), /* L4 based hash, proto can be unknown */
> + XDP_RSS_L4_TCP = BIT(4),
> + XDP_RSS_L4_UDP = BIT(5),
> + XDP_RSS_L4_SCTP = BIT(6),
> + XDP_RSS_L4_IPSEC = BIT(7), /* L4 based hash include IPSEC SPI */
> +};
> +
> +/* RSS hash type combinations used for driver HW mapping */
> +enum xdp_rss_hash_type {
> + XDP_RSS_TYPE_NONE = 0,
> + XDP_RSS_TYPE_L2 = XDP_RSS_TYPE_NONE,
> +
> + XDP_RSS_TYPE_L3_IPV4 = XDP_RSS_L3_IPV4,
> + XDP_RSS_TYPE_L3_IPV6 = XDP_RSS_L3_IPV6,
> + XDP_RSS_TYPE_L3_IPV4_OPT = XDP_RSS_L3_IPV4 | XDP_RSS_L3_DYNHDR,
> + XDP_RSS_TYPE_L3_IPV6_EX = XDP_RSS_L3_IPV6 | XDP_RSS_L3_DYNHDR,
> +
> + XDP_RSS_TYPE_L4_ANY = XDP_RSS_L4,
> + XDP_RSS_TYPE_L4_IPV4_TCP = XDP_RSS_L3_IPV4 | XDP_RSS_L4 |
> XDP_RSS_L4_TCP,
> + XDP_RSS_TYPE_L4_IPV4_UDP = XDP_RSS_L3_IPV4 | XDP_RSS_L4 |
> XDP_RSS_L4_UDP,
> + XDP_RSS_TYPE_L4_IPV4_SCTP = XDP_RSS_L3_IPV4 | XDP_RSS_L4 |
> XDP_RSS_L4_SCTP,
> +
> + XDP_RSS_TYPE_L4_IPV6_TCP = XDP_RSS_L3_IPV6 | XDP_RSS_L4 |
> XDP_RSS_L4_TCP,
> + XDP_RSS_TYPE_L4_IPV6_UDP = XDP_RSS_L3_IPV6 | XDP_RSS_L4 |
> XDP_RSS_L4_UDP,
> + XDP_RSS_TYPE_L4_IPV6_SCTP = XDP_RSS_L3_IPV6 | XDP_RSS_L4 |
> XDP_RSS_L4_SCTP,
> +
> + XDP_RSS_TYPE_L4_IPV6_TCP_EX = XDP_RSS_TYPE_L4_IPV6_TCP |
> XDP_RSS_L3_DYNHDR,
> + XDP_RSS_TYPE_L4_IPV6_UDP_EX = XDP_RSS_TYPE_L4_IPV6_UDP |
> XDP_RSS_L3_DYNHDR,
> + XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP|
> XDP_RSS_L3_DYNHDR,
> +};
> +
> #ifdef CONFIG_NET
> u32 bpf_xdp_metadata_kfunc_id(int id);
> bool bpf_dev_bound_kfunc_id(u32 btf_id);
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 528d4b37983d..38d2dee16b47 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -734,14 +734,22 @@ __bpf_kfunc int bpf_xdp_metadata_rx_timestamp(const
> struct xdp_md *ctx, u64 *tim
> * bpf_xdp_metadata_rx_hash - Read XDP frame RX hash.
> * @ctx: XDP context pointer.
> * @hash: Return value pointer.
> + * @rss_type: Return value pointer for RSS type.
> + *
> + * The RSS hash type (@rss_type) specifies what portion of packet
> headers NIC
> + * hardware were used when calculating RSS hash value. The type
> combinations
> + * are defined via &enum xdp_rss_hash_type and individual bits can be
> decoded
> + * via &enum xdp_rss_type_bits.
> *
> * Return:
> * * Returns 0 on success or ``-errno`` on error.
> * * ``-EOPNOTSUPP`` : means device driver doesn't implement kfunc
> * * ``-ENODATA`` : means no RX-hash available for this frame
> */
> -__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32
> *hash)
> +__bpf_kfunc int bpf_xdp_metadata_rx_hash(const struct xdp_md *ctx, u32
> *hash,
> + enum xdp_rss_hash_type *rss_type)
> {

[..]

> + BTF_TYPE_EMIT(enum xdp_rss_type_bits);

nit: Do we still need this with an extra argument?

> return -EOPNOTSUPP;
> }