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.

Fixes: 3d76a4d3d4e5 ("bpf: XDP metadata RX kfuncs")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
 include/linux/netdevice.h |    3 ++-
 include/net/xdp.h         |   45 +++++++++++++++++++++++++++++++++++++++++++++
 net/core/xdp.c            |   10 +++++++++-
 3 files changed, 56 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..216e910da1cf 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 +426,50 @@ XDP_METADATA_KFUNC_xxx
 MAX_XDP_METADATA_KFUNC,
 };
 
+enum xdp_rss_hash_type {
+	/* First part: Individual bits for L3/L4 types */
+	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 */
+
+	/* Second part: RSS hash type combinations used for driver HW mapping */
+	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..fb85aca81961 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -734,13 +734,21 @@ __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 used when calculating RSS hash value.  The RSS type can be decoded
+ * via &enum xdp_rss_hash_type either matching on individual L3/L4 bits
+ * ``XDP_RSS_L*`` or by combined traditional *RSS Hashing Types*
+ * ``XDP_RSS_TYPE_L*``.
  *
  * 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)
 {
 	return -EOPNOTSUPP;
 }

Hi Jesper,

I love your patch! Yet something to improve:

[auto build test ERROR on bpf/master]

url:    https://github.com/intel-lab-lkp/linux/commits/Jesper-Dangaard-Brouer/xdp-rss-hash-types-representation/20230331-230552
base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git master
patch link:    https://lore.kernel.org/r/168027498690.3941176.99100635661990098.stgit%40firesoul
patch subject: [PATCH bpf V4 1/5] xdp: rss hash types representation
config: ia64-allyesconfig (https://download.01.org/0day-ci/archive/20230401/202304010239.Jw6bKkWC-lkp@intel.com/config)
compiler: ia64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/9fcbbefa76e6e88a86426d13ed79ea24aacffe76
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Jesper-Dangaard-Brouer/xdp-rss-hash-types-representation/20230331-230552
        git checkout 9fcbbefa76e6e88a86426d13ed79ea24aacffe76
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=ia64 SHELL=/bin/bash drivers/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304010239.Jw6bKkWC-lkp@intel.com/

All errors (new ones prefixed by >>):

>> drivers/net/veth.c:1685:43: error: initialization of 'int (*)(const struct xdp_md *, u32 *, enum xdp_rss_hash_type *)' {aka 'int (*)(const struct xdp_md *, unsigned int *, enum xdp_rss_hash_type *)'} from incompatible pointer type 'int (*)(const struct xdp_md *, u32 *)' {aka 'int (*)(const struct xdp_md *, unsigned int *)'} [-Werror=incompatible-pointer-types]
    1685 |         .xmo_rx_hash                    = veth_xdp_rx_hash,
         |                                           ^~~~~~~~~~~~~~~~
   drivers/net/veth.c:1685:43: note: (near initialization for 'veth_xdp_metadata_ops.xmo_rx_hash')
   cc1: some warnings being treated as errors


vim +1685 drivers/net/veth.c

4456e7bdf74c9f Stephen Hemminger  2008-11-19  1682  
306531f0249f4e Stanislav Fomichev 2023-01-19  1683  static const struct xdp_metadata_ops veth_xdp_metadata_ops = {
306531f0249f4e Stanislav Fomichev 2023-01-19  1684  	.xmo_rx_timestamp		= veth_xdp_rx_timestamp,
306531f0249f4e Stanislav Fomichev 2023-01-19 @1685  	.xmo_rx_hash			= veth_xdp_rx_hash,
306531f0249f4e Stanislav Fomichev 2023-01-19  1686  };
306531f0249f4e Stanislav Fomichev 2023-01-19  1687  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests

Hopefully addressed in V5.

I obviously need to change function signature for all driver xmo_rx_hash
calls in patch 1/5 to make this compile.  I kept the RSS type
implementations for each driver as separate patches as this is more
reasonable to review and handle.


On 31/03/2023 20.23, kernel test robot wrote:
>
[...]
> All errors (new ones prefixed by >>):
> 
>>> drivers/net/veth.c:1685:43: error: initialization of 'int (*)(const struct xdp_md *, u32 *, enum xdp_rss_hash_type *)' {aka 'int (*)(const struct xdp_md *, unsigned int *, enum xdp_rss_hash_type *)'} from incompatible pointer type 'int (*)(const struct xdp_md *, u32 *)' {aka 'int (*)(const struct xdp_md *, unsigned int *)'} [-Werror=incompatible-pointer-types]
>      1685 |         .xmo_rx_hash                    = veth_xdp_rx_hash,
>           |                                           ^~~~~~~~~~~~~~~~
>     drivers/net/veth.c:1685:43: note: (near initialization for 'veth_xdp_metadata_ops.xmo_rx_hash')
>     cc1: some warnings being treated as errors