From: Jesper Dangaard Brouer <brouer@redhat.com>
To: "Björn Töpel" <bjorn.topel@gmail.com>
Cc: ast@kernel.org, daniel@iogearbox.net, davem@davemloft.net,
kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com,
netdev@vger.kernel.org, bpf@vger.kernel.org,
magnus.karlsson@intel.com, jonathan.lemon@gmail.com,
jeffrey.t.kirsher@intel.com,
"Björn Töpel" <bjorn.topel@intel.com>,
maximmi@mellanox.com, maciej.fijalkowski@intel.com
Subject: Re: [PATCH bpf-next v4 01/15] xsk: fix xsk_umem_xdp_frame_sz()
Date: Wed, 20 May 2020 15:18:19 +0200 [thread overview]
Message-ID: <20200520151819.1d2254b7@carbon> (raw)
In-Reply-To: <20200520094742.337678-2-bjorn.topel@gmail.com>
On Wed, 20 May 2020 11:47:28 +0200
Björn Töpel <bjorn.topel@gmail.com> wrote:
> From: Björn Töpel <bjorn.topel@intel.com>
>
> Calculating the "data_hard_end" for an XDP buffer coming from AF_XDP
> zero-copy mode, the return value of xsk_umem_xdp_frame_sz() is added
> to "data_hard_start".
>
> Currently, the chunk size of the UMEM is returned by
> xsk_umem_xdp_frame_sz(). This is not correct, if the fixed UMEM
> headroom is non-zero. Fix this by returning the chunk_size without the
> UMEM headroom.
>
> Fixes: 2a637c5b1aaf ("xdp: For Intel AF_XDP drivers add XDP frame_sz")
> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
> ---
> include/net/xdp_sock.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index abd72de25fa4..6b1137ce1692 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -239,7 +239,7 @@ static inline u64 xsk_umem_adjust_offset(struct xdp_umem *umem, u64 address,
>
> static inline u32 xsk_umem_xdp_frame_sz(struct xdp_umem *umem)
> {
> - return umem->chunk_size_nohr + umem->headroom;
> + return umem->chunk_size_nohr;
Hmm, is this correct?
As you write "xdp_data_hard_end" is calculated as an offset from
xdp->data_hard_start pointer based on the frame_sz. Will your
xdp->data_hard_start + frame_sz point to packet end?
#define xdp_data_hard_end(xdp) \
((xdp)->data_hard_start + (xdp)->frame_sz - \
SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
Note the macro reserves the last 320 bytes (for skb_shared_info), but
for AF_XDP zero-copy mode, it will never create an SKB that use this
area. Thus, in principle we can allow XDP-progs to extend/grow tail
into this area, but I don't think there is any use-case for this, as
it's much easier to access packet-data in userspace application.
(Thus, it might not be worth the complexity to give AF_XDP
bpf_xdp_adjust_tail access to this area, by e.g. "lying" via adding 320
bytes to frame_sz).
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
next prev parent reply other threads:[~2020-05-20 13:18 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-20 9:47 [PATCH bpf-next v4 00/15] Introduce AF_XDP buffer allocation API Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 01/15] xsk: fix xsk_umem_xdp_frame_sz() Björn Töpel
2020-05-20 13:18 ` Jesper Dangaard Brouer [this message]
2020-05-20 14:34 ` Björn Töpel
2020-05-21 4:29 ` Jesper Dangaard Brouer
2020-05-21 18:06 ` Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 02/15] xsk: move xskmap.c to net/xdp/ Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 03/15] xsk: move driver interface to xdp_sock_drv.h Björn Töpel
2020-05-20 16:57 ` Jakub Kicinski
2020-05-20 17:18 ` Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 04/15] xsk: move defines only used by AF_XDP internals to xsk.h Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 05/15] xsk: introduce AF_XDP buffer allocation API Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 06/15] i40e: refactor rx_bi accesses Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 07/15] i40e: separate kernel allocated rx_bi rings from AF_XDP rings Björn Töpel
2020-05-20 17:02 ` Jakub Kicinski
2020-05-20 17:19 ` Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 08/15] i40e, xsk: migrate to new MEM_TYPE_XSK_BUFF_POOL Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 09/15] ice, " Björn Töpel
2020-05-20 17:03 ` Jakub Kicinski
2020-05-20 17:20 ` Björn Töpel
2020-05-20 18:49 ` Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 10/15] ixgbe, " Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 11/15] mlx5, " Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 12/15] xsk: remove MEM_TYPE_ZERO_COPY and corresponding code Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 13/15] xdp: simplify xdp_return_{frame,frame_rx_napi,buff} Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 14/15] xsk: explicitly inline functions and move definitions Björn Töpel
2020-05-20 9:47 ` [PATCH bpf-next v4 15/15] MAINTAINERS, xsk: update AF_XDP section after moves/adds Björn Töpel
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