Re: [PATCH bpf-next v6 0/7] Add kfunc bpf_xdp_pull_data

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

On Fri, Sep 19, 2025 at 04:09:45PM -0700, Amery Hung wrote:
> v6 -> v5
>   patch 6
>   - v5 selftest failed on S390 when changing how tailroom occupied by
>     skb_shared_info is calculated. Revert selftest to v4, where we get
>     SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) by running an XDP
>     program

Hi Amery, could you shed more light on this? Would be nice to stick with
BTF approach as it looked clean to me. Was this due to SMP_CACHE_BYTES
being different between archs?

> 
> v5 -> v4
>   patch 1
>   - Add a new patch clearing pfmemalloc bit in xdp->frags when all frags
>     are freed in bpf_xdp_adjust_tail() (Maciej)
> 
>   patch 2
>   - Refactor bpf_xdp_shrink_data() (Maciej)
> 
>   patch 3
>   - Clear pfmemalloc when all frags are freed in bpf_xdp_pull_data()
>     (Maciej)
> 
>   patch 6
>   - Use BTF to get sizes of skb_shared_info and xdp_frame (Maciej)
> 
>   Link: https://lore.kernel.org/bpf/20250919182100.1925352-1-ameryhung@gmail.com/
> 
> v3 -> v4
>   patch 2
>   - Improve comments (Jakub)
>   - Drop new_end and len_free to simplify code (Jakub)
> 
>   patch 4
>   - Instead of adding is_xdp to bpf_test_init, move lower-bound check
>     of user_size to callers (Martin)
>   - Simplify linear data size calculation (Martin)
> 
>   patch 5
>   - Add static function identifier (Martin)
>   - Free calloc-ed buf (Martin)
> 
>   Link: https://lore.kernel.org/bpf/20250917225513.3388199-1-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
> 
>   Link: https://lore.kernel.org/bpf/20250915224801.2961360-1-ameryhung@gmail.com/
> 
> 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 separate 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.
> 
> 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 enabled always passse xdp_buff with empty linear
> data to xdp programs. xdp.test_xdp_native_pass_mb would fail to parse
> the header before this patchset.
> 
> Thanks!
> Amery
> 
> Amery Hung (7):
>   bpf: Clear pfmemalloc flag when freeing all fragments
>   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.h                             |   5 +
>  include/net/xdp_sock_drv.h                    |  21 +-
>  kernel/bpf/verifier.c                         |  13 ++
>  net/bpf/test_run.c                            |   9 +-
>  net/core/filter.c                             | 135 +++++++++++--
>  .../bpf/prog_tests/xdp_context_test_run.c     |   4 +-
>  .../selftests/bpf/prog_tests/xdp_pull_data.c  | 179 ++++++++++++++++++
>  .../selftests/bpf/progs/test_xdp_pull_data.c  |  48 +++++
>  .../selftests/net/lib/xdp_native.bpf.c        |  89 +++++++--
>  9 files changed, 463 insertions(+), 40 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
> 
> -- 
> 2.47.3
>