[PATCH bpf-next v3 0/6] Add kfunc bpf_xdp_pull_data

[Amery Hung <ameryhung@gmail.com>]

v2 -> v3
  Separate mlx5 fixes from the patchset

  Patch 2
  - Use headroom for pulling data by shifting metadata and data down
    (Jakub)
  - Drop the flags argument (Martin)

  Patch 4 
  - Support empty linear xdp data for BPF_PROG_TEST_RUN

v1 -> v2
  Rebase onto bpf-next

  Try to build on top of the mlx5 patchset that avoids copying payload
  to linear part by Christoph but got a kernel panic. Will rebase on
  that patchset if it got merged first, or seperate the mlx5 fix
  from this set.

  patch 1
  - Remove the unnecessary head frag search (Dragos)
  - Rewind the end frag pointer to simplify the change (Dragos)
  - Rewind the end frag pointer and recalculate truesize only when the
    number of frags changed (Dragos)

  patch 3
  - Fix len == zero behavior. To mirror bpf_skb_pull_data() correctly,
    the kfunc should do nothing (Stanislav)
  - Fix a pointer wrap around bug (Jakub)
  - Use memmove() when moving sinfo->frags (Jakub)

  Link: https://lore.kernel.org/bpf/20250905173352.3759457-1-ameryhung@gmail.com/
  
---

Hi all,

This patchset introduces a new kfunc bpf_xdp_pull_data() to allow
pulling nonlinear xdp data. This may be useful when a driver places
headers in fragments. When an xdp program would like to keep parsing
packet headers using direct packet access, it can call
bpf_xdp_pull_data() to make the header available in the linear data
area. The kfunc can also be used to decapsulate the header in the
nonlinear data, as currently there is no easy way to do this.

This patchset also tries to fix an issue in the mlx5 driver. The driver
curretly assumes the packet layout to be unchanged after xdp program
runs and may generate packet with corrupted data or trigger kernel warning
if xdp programs calls layout-changing kfunc such as bpf_xdp_adjust_tail(),
bpf_xdp_adjust_head() or bpf_xdp_pull_data() introduced in this set.

Tested with the added bpf selftest using bpf test_run and also on
mlx5 with the tools/testing/selftests/drivers/net/{xdp.py, ping.py}. mlx5
with striding RQ always pass xdp_buff with empty linear data to xdp
programs. xdp.test_xdp_native_pass_mb would fail to parse the header before
this patchset.

Grateful for any feedback (especially the driver part).

Thanks!
Amery

Amery Hung (6):
  bpf: Allow bpf_xdp_shrink_data to shrink a frag from head and tail
  bpf: Support pulling non-linear xdp data
  bpf: Clear packet pointers after changing packet data in kfuncs
  bpf: Support specifying linear xdp packet data size for
    BPF_PROG_TEST_RUN
  selftests/bpf: Test bpf_xdp_pull_data
  selftests: drv-net: Pull data before parsing headers

 include/net/xdp_sock_drv.h                    |  21 ++-
 kernel/bpf/verifier.c                         |  13 ++
 net/bpf/test_run.c                            |  26 ++-
 net/core/filter.c                             | 123 +++++++++++--
 .../bpf/prog_tests/xdp_context_test_run.c     |   4 +-
 .../selftests/bpf/prog_tests/xdp_pull_data.c  | 174 ++++++++++++++++++
 .../selftests/bpf/progs/test_xdp_pull_data.c  |  48 +++++
 .../selftests/net/lib/xdp_native.bpf.c        |  89 +++++++--
 8 files changed, 456 insertions(+), 42 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_pull_data.c
 create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_pull_data.c

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2.47.3