Re: [RFC bpf-next v1 0/7] Add kfunc bpf_xdp_pull_data

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 25 Aug 2025 12:39:11 -0700 Amery Hung wrote:
> 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 mlx5e 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
> mlx5e with the tools/testing/selftests/drivers/net/xdp.py. mlx5e with
> striding RQ will produce xdp_buff with empty linear data.
> xdp.test_xdp_native_pass_mb would fail to parse the header before this
> patchset.
> 
> Grateful for any feedback (especially the driver part).

CC: Gal, this is the correct way to resolve the XDP not having headers
in the first frag for mlx5.