[xdp-hints] Re: [PATCH bpf RFC 1/4] xdp: rss hash types representation

[Jesper Dangaard Brouer <jbrouer@redhat.com>]

On 29/03/2023 10.10, Edward Cree wrote:
> On 28/03/2023 21:15, Jesper Dangaard Brouer wrote:
>> 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 (xdp_rss_hash_type) that can both
>> be seen as a number that is ordered according by ISO layer, and can be bit
>> masked to separate IPv4 and IPv6 types for L4 protocols. Room is available
>> for extending later while keeping these properties. This maps and unifies
>> difference to hardware specific hashes.
> 
> Would it be better to make use of the ETHTOOL_GRXFH defines (stuff
>   like UDP_V6_FLOW, RXH_L4_B_0_1 etc.)?  Seems like that could allow
>   for some code reuse in drivers.

Thanks for the point to ethtool defines.
I can see that these are used when configuring the hardware RSS hash the
NIC should calculate.

From: include/uapi/linux/ethtool.h
  /* L3-L4 network traffic flow hash options */
  #define	RXH_L2DA	(1 << 1)
  #define	RXH_VLAN	(1 << 2)
  #define	RXH_L3_PROTO	(1 << 3)
  #define	RXH_IP_SRC	(1 << 4)
  #define	RXH_IP_DST	(1 << 5)
  #define	RXH_L4_B_0_1	(1 << 6) /* src port in case of TCP/UDP/SCTP */
  #define	RXH_L4_B_2_3	(1 << 7) /* dst port in case of TCP/UDP/SCTP */
  #define	RXH_DISCARD	(1 << 31)

I notice that I forgot about VLAN tag (RXH_VLAN) also can be part of the
hash calc in my proposed design.

It is interpreting to follow the possible ethool cmd->flow_type's:

  /* L2-L4 network traffic flow types */
  #define	TCP_V4_FLOW	0x01	/* hash or spec (tcp_ip4_spec) */
  #define	UDP_V4_FLOW	0x02	/* hash or spec (udp_ip4_spec) */
  #define	SCTP_V4_FLOW	0x03	/* hash or spec (sctp_ip4_spec) */
  #define	AH_ESP_V4_FLOW	0x04	/* hash only */
  #define	TCP_V6_FLOW	0x05	/* hash or spec (tcp_ip6_spec; nfc only) */
  #define	UDP_V6_FLOW	0x06	/* hash or spec (udp_ip6_spec; nfc only) */
  #define	SCTP_V6_FLOW	0x07	/* hash or spec (sctp_ip6_spec; nfc only) */
  #define	AH_ESP_V6_FLOW	0x08	/* hash only */
  #define	AH_V4_FLOW	0x09	/* hash or spec (ah_ip4_spec) */
  #define	ESP_V4_FLOW	0x0a	/* hash or spec (esp_ip4_spec) */
  #define	AH_V6_FLOW	0x0b	/* hash or spec (ah_ip6_spec; nfc only) */
  #define	ESP_V6_FLOW	0x0c	/* hash or spec (esp_ip6_spec; nfc only) */
  #define	IPV4_USER_FLOW	0x0d	/* spec only (usr_ip4_spec) */
  #define	IP_USER_FLOW	IPV4_USER_FLOW
  #define	IPV6_USER_FLOW	0x0e	/* spec only (usr_ip6_spec; nfc only) */
  #define	IPV4_FLOW	0x10	/* hash only */
  #define	IPV6_FLOW	0x11	/* hash only */
  #define	ETHER_FLOW	0x12	/* spec only (ether_spec) */
  /* Flag to enable additional fields in struct ethtool_rx_flow_spec */
  #define	FLOW_EXT	0x80000000
  #define	FLOW_MAC_EXT	0x40000000
  /* Flag to enable RSS spreading of traffic matching rule (nfc only) */
  #define	FLOW_RSS	0x20000000

It is clear that we need to support TCP+UDP+SCTP.

I assume the IPSEC is AH (Authentication Header) and ESP ( Encapsulating 
Security Payload.  Thus, (like I found with mlx5) we also need IPSET and 
maybe a bit (or number) for each protocol AH or ESP.

Both ah_ip4_spec and esp_ip4_spec points to ethtool.h struct:

/**
  * struct ethtool_ah_espip4_spec - flow specification for IPsec/IPv4
  * @ip4src: Source host
  * @ip4dst: Destination host
  * @spi: Security parameters index
  * @tos: Type-of-service
  *
  * This can be used to specify an IPsec transport or tunnel over IPv4.
  */
  struct ethtool_ah_espip4_spec {
	__be32	ip4src;
	__be32	ip4dst;
	__be32	spi;
	__u8    tos;
  };

Which confirms that it is the SPI that is the extra part of the hash.

--Jesper