Re: [PATCH v5 net 00/11] xsk: tailroom reservation and MTU validation

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Tue, Mar 31, 2026 at 05:02:02PM +0200, Maciej Fijalkowski wrote:

FWIW I'll be sending v6 as I messed up refcounting scheme on error path
for shared umem. I'm gonna also put on shelf driver cleanups as I got fed
up with issues reported by Sashiko. I plan to get back to it if I get to
work on forbidding mtu change feature on interfaces loaded with xsk
sockets.

> v4->v5:
> - add further review tags from Bjorn
> - fix ./test_progs -t xsk
>  * do so by making the procfs reading common so test_xsk.c can use it
> - get back to idea of relying on pool->umem->zc in
>   xsk_pool_get_tailroom(); that is because we now call its caller
>   (xsk_pool_get_rx_frame_size()) before getting down to driver via
>   ndo_bpf - we do it to rule out invalid setups in terms of MTU vs xsk
>   frame size/number of exposed segments by driver
> - bring back explicit rejection of mbuf && segs == 1 combo
> 
> v3->v4:
> - allow exact 128 bytes of space when user defined headroom is deducted
>   from total frame size
> - provide a routine for reading procfs entries within xskxceiver
>   * use it to fetch cache line size and calculate skb_shared_info size
>     on our own
> - clean up gve and igc xsk pool enablement routines
> - include mtu vs frame size * max zc segments validation in
>   xp_assign_dev()
> 
> v2->v3:
> - add tags from Bjorn/Stan
> - provide at least 128 bytes instead ETH_ZLEN when validating frame
>   headroom
>   * this way we can get rid of i40e/ice changes
>   * make sure xsk_pool_get_rx_frame_size() returns value 128b-aligned
>   * and remove pre-check from idpf
> - separate XDP_UMEM_SG_FLAG fixes from MTU validation in xsk_bind()
> - make drop_idx a local variable in xsk's xdp drop prog
> - adjust rx_dropped to new 128b related values
> - move ugly placed define (Bjorn)
> - remove READ_ONCE when fetching netdev->mtu (Bjorn)
> 
> v1->v2:
> - remove xsk_pool_get_tailroom() definition for !CONFIG_XDP_SOCKETS
>   (Stan)
> - do not rely on pool->umem->zc when configuring tailroom (Stan, Bjorn)
> - simplify dbuff setting in ZC drivers (Bjorn)
> - use defines for {head,tail}room in tests (Bjorn)
> - return EINVAL instead of EOPNOTSUPP when mtu setting is wrong (Bjorn)
> - include vlan headers and fcs length when validating mtu (Olek)
> - tighten umem headroom validation when registering umem (Sashiko AI)
> - set XDP_USE_SG in xp_assign_dev_shared() (Sashiko AI)
> - adjust rx dropped xskxceiver test
> 
> Hi,
> 
> here we fix a long-standing issue regarding multi-buffer scenario in ZC
> mode - we have not been providing space at the end of the buffer where
> multi-buffer XDP works on skb_shared_info. This has been brought to our
> attention via [0].
> 
> Unaligned mode does not get any specific treatment, it is user's
> responsibility to properly handle XSK addresses in queues.
> 
> With adjustments included here in this set against xskxceiver I have
> been able to pass the full test suite on ice.
> 
> Thanks,
> Maciej
> 
> [0]: https://community.intel.com/t5/Ethernet-Products/X710-XDP-Packet-Corruption-Issue-DRV-MODE-Zero-Copy-Multi-Buffer/m-p/1724208
> 
> 
> Maciej Fijalkowski (11):
>   xsk: tighten UMEM headroom validation to account for tailroom and min
>     frame
>   xsk: respect tailroom for ZC setups
>   xsk: fix XDP_UMEM_SG_FLAG issues
>   xsk: validate MTU against usable frame size on bind
>   selftests: bpf: introduce a common routine for reading procfs
>   selftests: bpf: fix pkt grow tests
>   selftests: bpf: have a separate variable for drop test
>   selftests: bpf: adjust rx_dropped xskxceiver's test to respect
>     tailroom
>   idpf: remove xsk frame size check against alignment
>   igc: remove home-grown xsk's frame size validation
>   gve: remove home-grown xsk's frame size validation
> 
>  drivers/net/ethernet/google/gve/gve_main.c    |  5 --
>  drivers/net/ethernet/intel/idpf/xsk.c         | 10 ----
>  drivers/net/ethernet/intel/igc/igc_xdp.c      | 11 ----
>  include/net/xdp_sock.h                        |  2 +-
>  include/net/xdp_sock_drv.h                    | 17 +++++-
>  net/xdp/xdp_umem.c                            |  3 +-
>  net/xdp/xsk_buff_pool.c                       | 25 ++++++++-
>  .../selftests/bpf/prog_tests/test_xsk.c       | 55 +++++++++----------
>  .../selftests/bpf/prog_tests/test_xsk.h       | 23 ++++++++
>  tools/testing/selftests/bpf/prog_tests/xsk.c  | 19 +++++++
>  .../selftests/bpf/progs/xsk_xdp_progs.c       |  4 +-
>  tools/testing/selftests/bpf/xskxceiver.c      | 23 ++++++++
>  12 files changed, 135 insertions(+), 62 deletions(-)
> 
> -- 
> 2.43.0
>