> Lorenzo Bianconi wrote:
> > This series introduce XDP multi-buffer support. The mvneta driver is
> > the first to support these new "non-linear" xdp_{buff,frame}. Reviewers
> > please focus on how these new types of xdp_{buff,frame} packets
> > traverse the different layers and the layout design. It is on purpose
> > that BPF-helpers are kept simple, as we don't want to expose the
> > internal layout to allow later changes.
> >
> > The main idea for the new multi-buffer layout is to reuse the same
> > structure used for non-linear SKB. This rely on the "skb_shared_info"
> > struct at the end of the first buffer to link together subsequent
> > buffers. Keeping the layout compatible with SKBs is also done to ease
> > and speedup creating a SKB from an xdp_{buff,frame}.
> > Converting xdp_frame to SKB and deliver it to the network stack is shown
> > in patch 05/18 (e.g. cpumaps).
> >
> > A multi-buffer bit (mb) has been introduced in the flags field of xdp_{buff,frame}
> > structure to notify the bpf/network layer if this is a xdp multi-buffer frame
> > (mb = 1) or not (mb = 0).
> > The mb bit will be set by a xdp multi-buffer capable driver only for
> > non-linear frames maintaining the capability to receive linear frames
> > without any extra cost since the skb_shared_info structure at the end
> > of the first buffer will be initialized only if mb is set.
> > Moreover the flags field in xdp_{buff,frame} will be reused even for
> > xdp rx csum offloading in future series.
> >
>
> The series is looking really close to me. Couple small comments/questions
> inline. Also I think we should call out the potential issues in the cover
> letter with regards to backwards compatibility. Something like,
>
> "
> A multi-buffer enabled NIC may receive XDP frames with multiple frags.
> If a BPF program does not understand mb layouts its possible to contrive
> a BPF program that incorrectly views data_end as the end of data when
> there is more data in the payload. Note helpers will generally due the
> correct thing, for example perf_output will consume entire payload. But,
> it is still possible some programs could do the wrong thing even if in
> an edge case. Although we expect most BPF programs not to be impacted
> we can't rule out, you've been warned.
ack, I will add it to the cover letter in v13.
Regards,
Lorenzo
> "
>
> I can't think of an elegant way around this and it does require at least
> some type of opt-in by increasing the MTU limit so I'm OK with it given
> I think it should impact few (no?) real programs.
>
> > Typical use cases for this series are:
> > - Jumbo-frames
> > - Packet header split (please see Google���s use-case @ NetDevConf 0x14, [0])
> > - TSO/GRO
> >
> > The two following ebpf helpers (and related selftests) has been introduced:
> > - bpf_xdp_adjust_data:
> > Move xdp_md->data and xdp_md->data_end pointers in subsequent fragments
> > according to the offset provided by the ebpf program. This helper can be
> > used to read/write values in frame payload.
> > - bpf_xdp_get_buff_len:
> > Return the total frame size (linear + paged parts)
> >
> > bpf_xdp_adjust_tail and bpf_xdp_copy helpers have been modified to take into
> > account xdp multi-buff frames.
> >
> > More info about the main idea behind this approach can be found here [1][2].
> >
> > Changes since v11:
> > - add missing static to bpf_xdp_get_buff_len_proto structure
> > - fix bpf_xdp_adjust_data helper when offset is smaller than linear area length.
> >
> > Changes since v10:
> > - move xdp->data to the requested payload offset instead of to the beginning of
> > the fragment in bpf_xdp_adjust_data()
> >
> > Changes since v9:
> > - introduce bpf_xdp_adjust_data helper and related selftest
> > - add xdp_frags_size and xdp_frags_tsize fields in skb_shared_info
> > - introduce xdp_update_skb_shared_info utility routine in ordere to not reset
> > frags array in skb_shared_info converting from a xdp_buff/xdp_frame to a skb
> > - simplify bpf_xdp_copy routine
> >
> > Changes since v8:
> > - add proper dma unmapping if XDP_TX fails on mvneta for a xdp multi-buff
> > - switch back to skb_shared_info implementation from previous xdp_shared_info
> > one
> > - avoid using a bietfield in xdp_buff/xdp_frame since it introduces performance
> > regressions. Tested now on 10G NIC (ixgbe) to verify there are no performance
> > penalties for regular codebase
> > - add bpf_xdp_get_buff_len helper and remove frame_length field in xdp ctx
> > - add data_len field in skb_shared_info struct
> > - introduce XDP_FLAGS_FRAGS_PF_MEMALLOC flag
> >
> > Changes since v7:
> > - rebase on top of bpf-next
> > - fix sparse warnings
> > - improve comments for frame_length in include/net/xdp.h
> >
> > Changes since v6:
> > - the main difference respect to previous versions is the new approach proposed
> > by Eelco to pass full length of the packet to eBPF layer in XDP context
> > - reintroduce multi-buff support to eBPF kself-tests
> > - reintroduce multi-buff support to bpf_xdp_adjust_tail helper
> > - introduce multi-buffer support to bpf_xdp_copy helper
> > - rebase on top of bpf-next
> >
> > Changes since v5:
> > - rebase on top of bpf-next
> > - initialize mb bit in xdp_init_buff() and drop per-driver initialization
> > - drop xdp->mb initialization in xdp_convert_zc_to_xdp_frame()
> > - postpone introduction of frame_length field in XDP ctx to another series
> > - minor changes
> >
> > Changes since v4:
> > - rebase ontop of bpf-next
> > - introduce xdp_shared_info to build xdp multi-buff instead of using the
> > skb_shared_info struct
> > - introduce frame_length in xdp ctx
> > - drop previous bpf helpers
> > - fix bpf_xdp_adjust_tail for xdp multi-buff
> > - introduce xdp multi-buff self-tests for bpf_xdp_adjust_tail
> > - fix xdp_return_frame_bulk for xdp multi-buff
> >
> > Changes since v3:
> > - rebase ontop of bpf-next
> > - add patch 10/13 to copy back paged data from a xdp multi-buff frame to
> > userspace buffer for xdp multi-buff selftests
> >
> > Changes since v2:
> > - add throughput measurements
> > - drop bpf_xdp_adjust_mb_header bpf helper
> > - introduce selftest for xdp multibuffer
> > - addressed comments on bpf_xdp_get_frags_count
> > - introduce xdp multi-buff support to cpumaps
> >
> > Changes since v1:
> > - Fix use-after-free in xdp_return_{buff/frame}
> > - Introduce bpf helpers
> > - Introduce xdp_mb sample program
> > - access skb_shared_info->nr_frags only on the last fragment
> >
> > Changes since RFC:
> > - squash multi-buffer bit initialization in a single patch
> > - add mvneta non-linear XDP buff support for tx side
> >
> > [0] https://netdevconf.info/0x14/session.html?talk-the-path-to-tcp-4k-mtu-and-rx-zerocopy
> > [1] https://github.com/xdp-project/xdp-project/blob/master/areas/core/xdp-multi-buffer01-design.org
> > [2] https://netdevconf.info/0x14/session.html?tutorial-add-XDP-support-to-a-NIC-driver (XDPmulti-buffers section)
> >
> > Eelco Chaudron (3):
> > bpf: add multi-buff support to the bpf_xdp_adjust_tail() API
> > bpf: add multi-buffer support to xdp copy helpers
> > bpf: update xdp_adjust_tail selftest to include multi-buffer
> >
> > Lorenzo Bianconi (15):
> > net: skbuff: add size metadata to skb_shared_info for xdp
> > xdp: introduce flags field in xdp_buff/xdp_frame
> > net: mvneta: update mb bit before passing the xdp buffer to eBPF layer
> > net: mvneta: simplify mvneta_swbm_add_rx_fragment management
> > net: xdp: add xdp_update_skb_shared_info utility routine
> > net: marvell: rely on xdp_update_skb_shared_info utility routine
> > xdp: add multi-buff support to xdp_return_{buff/frame}
> > net: mvneta: add multi buffer support to XDP_TX
> > net: mvneta: enable jumbo frames for XDP
> > bpf: introduce bpf_xdp_get_buff_len helper
> > bpf: move user_size out of bpf_test_init
> > bpf: introduce multibuff support to bpf_prog_test_run_xdp()
> > bpf: test_run: add xdp_shared_info pointer in bpf_test_finish
> > signature
> > net: xdp: introduce bpf_xdp_adjust_data helper
> > bpf: add bpf_xdp_adjust_data selftest
> >
> > drivers/net/ethernet/marvell/mvneta.c | 204 ++++++++++-------
> > include/linux/skbuff.h | 6 +-
> > include/net/xdp.h | 95 +++++++-
> > include/uapi/linux/bpf.h | 39 ++++
> > kernel/trace/bpf_trace.c | 3 +
> > net/bpf/test_run.c | 117 ++++++++--
> > net/core/filter.c | 213 +++++++++++++++++-
> > net/core/xdp.c | 76 ++++++-
> > tools/include/uapi/linux/bpf.h | 39 ++++
> > .../bpf/prog_tests/xdp_adjust_data.c | 55 +++++
> > .../bpf/prog_tests/xdp_adjust_tail.c | 118 ++++++++++
> > .../selftests/bpf/prog_tests/xdp_bpf2bpf.c | 151 +++++++++----
> > .../bpf/progs/test_xdp_adjust_tail_grow.c | 10 +-
> > .../bpf/progs/test_xdp_adjust_tail_shrink.c | 32 ++-
> > .../selftests/bpf/progs/test_xdp_bpf2bpf.c | 2 +-
> > .../bpf/progs/test_xdp_update_frags.c | 41 ++++
> > 16 files changed, 1036 insertions(+), 165 deletions(-)
> > create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_adjust_data.c
> > create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_update_frags.c
> >
> > --
> > 2.31.1
> >
>
>
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