Subject: Re: [PATCH v21 bpf-next 00/23] mvneta: introduce XDP multi-buffer support

From: Lorenzo Bianconi <[email-masked]>
Date: Wed, 12 Jan 2022 19:55:56 +0100

@Daniel: Alexei reported you have some comments about the series.
Any objections about posting v22?

Regards,
Lorenzo

> 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.
> 
> Typical use cases for this series are:
> - Jumbo-frames
> - Packet header split (please see Google’s use-case @ NetDevConf 0x14, [0])
> - TSO/GRO for XDP_REDIRECT
> 
> The three following ebpf helpers (and related selftests) has been introduced:
> - bpf_xdp_load_bytes:
>   This helper is provided as an easy way to load data from a xdp buffer. It
>   can be used to load len bytes from offset from the frame associated to
>   xdp_md, into the buffer pointed by buf.
> - bpf_xdp_store_bytes:
>   Store len bytes from buffer buf into the frame associated to xdp_md, at
>   offset.
> - 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.
> Moreover, similar to skb_header_pointer, we introduced bpf_xdp_pointer utility
> routine to return a pointer to a given position in the xdp_buff if the
> requested area (offset + len) is contained in a contiguous memory area
> otherwise it must be copied in a bounce buffer provided by the caller running
> bpf_xdp_copy_buf().
> 
> BPF_F_XDP_MB flag for bpf_attr has been introduced to notify the kernel the
> eBPF program fully support xdp multi-buffer.
> SEC("xdp_mb/"), SEC_DEF("xdp_devmap_mb/") and SEC_DEF("xdp_cpumap_mb/" have been
> introduced to declare xdp multi-buffer support.
> The NIC driver is expected to reject an eBPF program if it is running in XDP
> multi-buffer mode and the program does not support XDP multi-buffer.
> In the same way it is not possible to mix xdp multi-buffer and xdp legacy
> programs in a CPUMAP/DEVMAP or tailcall a xdp multi-buffer/legacy program from
> a legacy/multi-buff one.
> 
> More info about the main idea behind this approach can be found here [1][2].
> 
> Changes since v20:
> - rebase to current bpf-next
> 
> Changes since v19:
> - do not run deprecated bpf_prog_load()
> - rely on skb_frag_size_add/skb_frag_size_sub in
>   bpf_xdp_mb_increase_tail/bpf_xdp_mb_shrink_tail
> - rely on sinfo->nr_frags in bpf_xdp_mb_shrink_tail to check if the frame has
>   been shrunk to a single-buffer one
> - allow XDP_REDIRECT of a xdp-mb frame into a CPUMAP
> 
> Changes since v18:
> - fix bpf_xdp_copy_buf utility routine when we want to load/store data
>   contained in frag<n>
> - add a selftest for bpf_xdp_load_bytes/bpf_xdp_store_bytes when the caller
>   accesses data contained in frag<n> and frag<n+1>
> 
> Changes since v17:
> - rework bpf_xdp_copy to squash base and frag management
> - remove unused variable in bpf_xdp_mb_shrink_tail()
> - move bpf_xdp_copy_buf() out of bpf_xdp_pointer()
> - add sanity check for len in bpf_xdp_pointer()
> - remove EXPORT_SYMBOL for __xdp_return()
> - introduce frag_size field in xdp_rxq_info to let the driver specify max value
>   for xdp fragments. frag_size set to 0 means the tail increase of last the
>   fragment is not supported.
> 
> Changes since v16:
> - do not allow tailcalling a xdp multi-buffer/legacy program from a
>   legacy/multi-buff one.
> - do not allow mixing xdp multi-buffer and xdp legacy programs in a
>   CPUMAP/DEVMAP
> - add selftests for CPUMAP/DEVMAP xdp mb compatibility
> - disable XDP_REDIRECT for xdp multi-buff for the moment
> - set max offset value to 0xffff in bpf_xdp_pointer
> - use ARG_PTR_TO_UNINIT_MEM and ARG_CONST_SIZE for arg3_type and arg4_type
>   of bpf_xdp_store_bytes/bpf_xdp_load_bytes
> 
> Changes since v15:
> - let the verifier check buf is not NULL in
>   bpf_xdp_load_bytes/bpf_xdp_store_bytes helpers
> - return an error if offset + length is over frame boundaries in
>   bpf_xdp_pointer routine
> - introduce BPF_F_XDP_MB flag for bpf_attr to notify the kernel the eBPF
>   program fully supports xdp multi-buffer.
> - reject a non XDP multi-buffer program if the driver is running in
>   XDP multi-buffer mode.
> 
> Changes since v14:
> - intrudce bpf_xdp_pointer utility routine and
>   bpf_xdp_load_bytes/bpf_xdp_store_bytes helpers
> - drop bpf_xdp_adjust_data helper
> - drop xdp_frags_truesize in skb_shared_info
> - explode bpf_xdp_mb_adjust_tail in bpf_xdp_mb_increase_tail and
>   bpf_xdp_mb_shrink_tail
> 
> Changes since v13:
> - use u32 for xdp_buff/xdp_frame flags field
> - rename xdp_frags_tsize in xdp_frags_truesize
> - fixed comments
> 
> Changes since v12:
> - fix bpf_xdp_adjust_data helper for single-buffer use case
> - return -EFAULT in bpf_xdp_adjust_{head,tail} in case the data pointers are not
>   properly reset
> - collect ACKs from John
> 
> 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: selftests: update xdp_adjust_tail selftest to include
>     multi-buffer
> 
> Lorenzo Bianconi (19):
>   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
>   bpf: introduce BPF_F_XDP_MB flag in prog_flags loading the ebpf
>     program
>   net: mvneta: enable jumbo frames if the loaded XDP program support mb
>   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
>   libbpf: Add SEC name for xdp_mb programs
>   net: xdp: introduce bpf_xdp_pointer utility routine
>   bpf: selftests: introduce bpf_xdp_{load,store}_bytes selftest
>   bpf: selftests: add CPUMAP/DEVMAP selftests for xdp multi-buff
>   xdp: disable XDP_REDIRECT for xdp multi-buff
> 
> Toke Hoiland-Jorgensen (1):
>   bpf: generalise tail call map compatibility check
> 
>  drivers/net/ethernet/marvell/mvneta.c         | 204 +++++++++------
>  include/linux/bpf.h                           |  31 ++-
>  include/linux/skbuff.h                        |   1 +
>  include/net/xdp.h                             | 108 +++++++-
>  include/uapi/linux/bpf.h                      |  30 +++
>  kernel/bpf/arraymap.c                         |   4 +-
>  kernel/bpf/core.c                             |  28 +-
>  kernel/bpf/cpumap.c                           |   8 +-
>  kernel/bpf/devmap.c                           |   3 +-
>  kernel/bpf/syscall.c                          |  25 +-
>  kernel/trace/bpf_trace.c                      |   3 +
>  net/bpf/test_run.c                            | 115 +++++++--
>  net/core/filter.c                             | 244 +++++++++++++++++-
>  net/core/xdp.c                                |  78 +++++-
>  tools/include/uapi/linux/bpf.h                |  30 +++
>  tools/lib/bpf/libbpf.c                        |   8 +
>  .../bpf/prog_tests/xdp_adjust_frags.c         | 103 ++++++++
>  .../bpf/prog_tests/xdp_adjust_tail.c          | 131 ++++++++++
>  .../selftests/bpf/prog_tests/xdp_bpf2bpf.c    | 151 ++++++++---
>  .../bpf/prog_tests/xdp_cpumap_attach.c        |  65 ++++-
>  .../bpf/prog_tests/xdp_devmap_attach.c        |  56 ++++
>  .../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         |  42 +++
>  .../bpf/progs/test_xdp_with_cpumap_helpers.c  |   6 +
>  .../progs/test_xdp_with_cpumap_mb_helpers.c   |  27 ++
>  .../bpf/progs/test_xdp_with_devmap_helpers.c  |   7 +
>  .../progs/test_xdp_with_devmap_mb_helpers.c   |  27 ++
>  29 files changed, 1367 insertions(+), 212 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/xdp_adjust_frags.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_update_frags.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_with_cpumap_mb_helpers.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_xdp_with_devmap_mb_helpers.c
> 
> -- 
> 2.33.1
>