[PATCH v6 net 0/8] xsk: tailroom reservation and MTU validation

Maciej Fijalkowski
2026-04-02T15:50:30Z

v5->v6:
- refrain from relying on umem refcnt when disabling zc on error path
(Sashiko)
- have a separate __xsk_pool_get_rx_frame_size() which preserves old
behavior and use it on copy path (Sashiko)
- drop driver cleanups

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 (8):
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

include/net/xdp_sock.h | 2 +-
include/net/xdp_sock_drv.h | 23 +++++++-
net/xdp/xdp_umem.c | 3 +-
net/xdp/xsk.c | 4 +-
net/xdp/xsk_buff_pool.c | 32 ++++++++++-
.../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 ++++++++
10 files changed, 150 insertions(+), 38 deletions(-)

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2.43.0