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Message-ID: <CAMB2axPh4Ax=+1vzzm_AiWN8KKMwydLh=aUhqpd2x8rLT18yzw@mail.gmail.com>
Date: Mon, 22 Sep 2025 10:46:39 -0700
From: Amery Hung <ameryhung@...il.com>
To: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc: bpf@...r.kernel.org, netdev@...r.kernel.org, alexei.starovoitov@...il.com,
andrii@...nel.org, daniel@...earbox.net, paul.chaignon@...il.com,
kuba@...nel.org, stfomichev@...il.com, martin.lau@...nel.org,
mohsin.bashr@...il.com, noren@...dia.com, dtatulea@...dia.com,
saeedm@...dia.com, tariqt@...dia.com, mbloch@...dia.com, kernel-team@...a.com
Subject: Re: [PATCH bpf-next v6 0/7] Add kfunc bpf_xdp_pull_data
On Mon, Sep 22, 2025 at 8:06 AM Maciej Fijalkowski
<maciej.fijalkowski@...el.com> wrote:
>
> 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?
Right.
I think it would be simpler to just find the tailroom occupied by
skb_shared_info by running an XDP program instead of trying to
duplicate how the kernel derives that size in the user space.
WDYT?
>
> >
> > 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
> >
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