Date:   Wed, 28 Jul 2021 11:47:28 +0200
From:   Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
To:     Lorenzo Bianconi <me@...enzobianconi.net>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, davem@...emloft.net,
        kuba@...nel.org, ast@...nel.org, daniel@...earbox.net,
        shayagr@...zon.com, john.fastabend@...il.com, dsahern@...nel.org,
        brouer@...hat.com, echaudro@...hat.com, jasowang@...hat.com,
        alexander.duyck@...il.com, saeed@...nel.org,
        maciej.fijalkowski@...el.com, magnus.karlsson@...el.com,
        tirthendu.sarkar@...el.com, toke@...hat.com,
        Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH v10 bpf-next 00/18] mvneta: introduce XDP multi-buffer
 support

> From: Lorenzo Bianconi <lorenzo@...nel.org>
> 
> 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.

I sent the cover-letter. Sorry for the noise.

Regards,
Lorenzo

> 
> The main idea for the new multi-buffer layout is to reuse the same
> layout 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.
> 
> Typical use cases for this series are:
> - Jumbo-frames
> - Packet header split (please see Google’s use-case @ NetDevConf 0x14, [0])
> - TSO
> 
> 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 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         | 213 ++++++++++--------
>  include/linux/skbuff.h                        |   6 +-
>  include/net/xdp.h                             |  95 +++++++-
>  include/uapi/linux/bpf.h                      |  38 ++++
>  kernel/trace/bpf_trace.c                      |   3 +
>  net/bpf/test_run.c                            | 117 ++++++++--
>  net/core/filter.c                             | 210 ++++++++++++++++-
>  net/core/xdp.c                                |  76 ++++++-
>  tools/include/uapi/linux/bpf.h                |  38 ++++
>  .../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         |  49 ++++
>  16 files changed, 1044 insertions(+), 169 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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