From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Saeed Mahameed <saeedm@mellanox.com>
Cc: "toke@redhat.com" <toke@redhat.com>,
"gtzalik@amazon.com" <gtzalik@amazon.com>,
"ilias.apalodimas@linaro.org" <ilias.apalodimas@linaro.org>,
"borkmann@iogearbox.net" <borkmann@iogearbox.net>,
"alexander.duyck@gmail.com" <alexander.duyck@gmail.com>,
"john.fastabend@gmail.com" <john.fastabend@gmail.com>,
"akiyano@amazon.com" <akiyano@amazon.com>,
"zorik@amazon.com" <zorik@amazon.com>,
"alexei.starovoitov@gmail.com" <alexei.starovoitov@gmail.com>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"jeffrey.t.kirsher@intel.com" <jeffrey.t.kirsher@intel.com>,
"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
"dsahern@gmail.com" <dsahern@gmail.com>,
"lorenzo@kernel.org" <lorenzo@kernel.org>,
"willemdebruijn.kernel@gmail.com"
<willemdebruijn.kernel@gmail.com>,
brouer@redhat.com,
Steffen Klassert <steffen.klassert@secunet.com>,
Willy Tarreau <w@1wt.eu>
Subject: Re: [PATCH RFC v2 29/33] xdp: allow bpf_xdp_adjust_tail() to grow packet size
Date: Tue, 14 Apr 2020 14:46:37 +0200 [thread overview]
Message-ID: <20200414144637.0dafdda5@carbon> (raw)
In-Reply-To: <ed0ce4d76e77b23aa3edcd821d5a4867e8bb27b1.camel@mellanox.com>
On Thu, 9 Apr 2020 03:31:14 +0000
Saeed Mahameed <saeedm@mellanox.com> wrote:
> On Wed, 2020-04-08 at 13:53 +0200, Jesper Dangaard Brouer wrote:
> > Finally, after all drivers have a frame size, allow BPF-helper
> > bpf_xdp_adjust_tail() to grow or extend packet size at frame tail.
> >
>
> can you provide a list of usecases for why tail extension is necessary
> ?
Use-cases:
(1) IPsec / XFRM needs a tail extend[1][2].
(2) DNS-cache replies in XDP.
(3) HA-proxy ALOHA would need it to convert to XDP.
> and what do you have in mind as immediate use of bpf_xdp_adjust_tail()
> ?
I guess Steffen Klassert's ipsec use-case(1) it the most immediate.
[1] http://vger.kernel.org/netconf2019_files/xfrm_xdp.pdf
[2] http://vger.kernel.org/netconf2019.html
> both cover letter and commit messages didn't list any actual use case..
Sorry about that.
> > Remember that helper/macro xdp_data_hard_end have reserved some
> > tailroom. Thus, this helper makes sure that the BPF-prog don't have
> > access to this tailroom area.
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > ---
> > include/uapi/linux/bpf.h | 4 ++--
> > net/core/filter.c | 18 ++++++++++++++++--
> > 2 files changed, 18 insertions(+), 4 deletions(-)
> >
[... cut ...]
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 7628b947dbc3..4d58a147eed0 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -3422,12 +3422,26 @@ static const struct bpf_func_proto
> > bpf_xdp_adjust_head_proto = {
> >
> > BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
> > {
> > + void *data_hard_end = xdp_data_hard_end(xdp);
> > void *data_end = xdp->data_end + offset;
> >
> > - /* only shrinking is allowed for now. */
> > - if (unlikely(offset >= 0))
> > + /* Notice that xdp_data_hard_end have reserved some tailroom */
> > + if (unlikely(data_end > data_hard_end))
> > return -EINVAL;
> >
>
> i don't know if i like this approach for couple of reasons.
>
> 1. drivers will provide arbitrary frames_sz, which is normally larger
> than mtu, and could be a full page size, for XDP_TX action this can be
> problematic if xdp progs will allow oversized packets to get caught at
> the driver level..
We already check if MTU is exceeded for a specific device when we
redirect into this, see helper xdp_ok_fwd_dev(). For the XDP_TX case,
I guess some drivers bypass that check, which should be fixed. The
XDP_TX case is IMHO a place where we allow drivers do special
optimizations, thus drivers can choose to do something faster than
calling generic helper xdp_ok_fwd_dev().
>
> 2. xdp_data_hard_end(xdp) has a hardcoded assumption of the skb shinfo
> and it introduces a reverse dependency between xdp buff and skbuff
>
(I'll address this in another mail)
> both of the above can be solved if the drivers provided the max
> allowed frame size, already accounting for mtu and shinfo when setting
> xdp_buff.frame_sz at the driver level.
It seems we look at the problem from two different angles. You have
the drivers perspective, while I have the network stacks perspective
(the XDP_PASS case). The mlx5 driver treats XDP as a special case, by
hiding or confining xdp_buff to functions fairly deep in the
call-stack. My goal is different (moving SKB out of drivers), I see
the xdp_buff/xdp_frame as the main packet object in the drivers, that
gets send up the network stack (after converting to xdp_frame) and
converted into SKB in core-code (yes, there is a long road-ahead). The
larger tailroom can be used by netstack in SKB-coalesce.
The next step is making xdp_buff (and xdp_frame) multi-buffer aware.
This is why I reserve room for skb_shared_info. I have considered
reducing the size of xdp_buff.frame_sz, with sizeof(skb_shared_info),
but it got kind of ugly having this in each drivers.
I also considered having drivers setup a direct pointer to
{skb,xdp}_shared_info section in xdp_buff, because will make it more
flexible (for what I imagined Alexander Duyck want). (But we can still
do/change that later, once we start work in multi-buffer code)
--
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:[~2020-04-14 12:47 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <158634658714.707275.7903484085370879864.stgit@firesoul>
2020-04-08 11:50 ` [PATCH RFC v2 01/33] xdp: add frame size to xdp_buff Jesper Dangaard Brouer
2020-04-08 17:53 ` Jakub Kicinski
2020-04-09 0:48 ` Saeed Mahameed
2020-04-09 1:13 ` Jakub Kicinski
2020-04-09 23:07 ` Saeed Mahameed
2020-04-09 23:27 ` Jakub Kicinski
2020-04-14 14:16 ` Jesper Dangaard Brouer
2020-04-09 0:50 ` Saeed Mahameed
2020-04-16 13:02 ` Jesper Dangaard Brouer
2020-04-17 23:09 ` Saeed Mahameed
2020-04-08 11:50 ` [PATCH RFC v2 02/33] bnxt: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-08 11:50 ` [PATCH RFC v2 03/33] sfc: add XDP frame size Jesper Dangaard Brouer
2020-04-08 11:50 ` [PATCH RFC v2 04/33] mvneta: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-08 11:50 ` [PATCH RFC v2 05/33] net: netsec: Add support for XDP frame size Jesper Dangaard Brouer
2020-04-08 13:09 ` Lorenzo Bianconi
2020-04-14 8:07 ` Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 06/33] net: XDP-generic determining " Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 07/33] xdp: xdp_frame add member frame_sz and handle in convert_to_xdp_frame Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 08/33] xdp: cpumap redirect use frame_sz and increase skb_tailroom Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 09/33] veth: adjust hard_start offset on redirect XDP frames Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 10/33] veth: xdp using frame_sz in veth driver Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 11/33] dpaa2-eth: add XDP frame size Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 12/33] hv_netvsc: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-08 14:56 ` Haiyang Zhang
2020-04-08 11:51 ` [PATCH RFC v2 13/33] qlogic/qede: " Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 14/33] net: ethernet: ti: add XDP frame size to driver cpsw Jesper Dangaard Brouer
2020-04-08 11:51 ` [PATCH RFC v2 15/33] ena: add XDP frame size to amazon NIC driver Jesper Dangaard Brouer
2020-04-22 8:39 ` Jubran, Samih
2020-04-08 11:51 ` [PATCH RFC v2 16/33] mlx4: add XDP frame size and adjust max XDP MTU Jesper Dangaard Brouer
2020-04-08 12:57 ` Tariq Toukan
2020-04-14 8:19 ` Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 17/33] mlx5: rx queue setup time determine frame_sz for XDP Jesper Dangaard Brouer
2020-04-08 12:52 ` Tariq Toukan
2020-04-16 12:04 ` Jesper Dangaard Brouer
2020-04-09 9:28 ` Maxim Mikityanskiy
2020-04-08 11:52 ` [PATCH RFC v2 18/33] net: thunderx: add XDP frame size Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 19/33] nfp: add XDP frame size to netronome driver Jesper Dangaard Brouer
2020-04-08 17:53 ` Jakub Kicinski
2020-04-14 14:02 ` Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 20/33] tun: add XDP frame size Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 21/33] vhost_net: also populate " Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 22/33] virtio_net: add XDP frame size in two code paths Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 23/33] ixgbe: fix XDP redirect on archs with PAGE_SIZE above 4K Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 24/33] ixgbe: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 25/33] ixgbevf: add XDP frame size to VF driver Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 26/33] i40e: add XDP frame size to driver Jesper Dangaard Brouer
2020-04-08 21:48 ` David Miller
2020-04-14 10:16 ` Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 27/33] ice: " Jesper Dangaard Brouer
2020-04-08 11:52 ` [PATCH RFC v2 28/33] xdp: for Intel AF_XDP drivers add XDP frame_sz Jesper Dangaard Brouer
2020-04-08 17:31 ` Björn Töpel
2020-04-09 9:33 ` Maxim Mikityanskiy
2020-04-08 11:53 ` [PATCH RFC v2 29/33] xdp: allow bpf_xdp_adjust_tail() to grow packet size Jesper Dangaard Brouer
2020-04-09 3:31 ` Saeed Mahameed
2020-04-14 12:46 ` Jesper Dangaard Brouer [this message]
2020-04-18 3:33 ` Saeed Mahameed
2020-04-14 9:56 ` Jesper Dangaard Brouer
2020-04-14 10:11 ` Toke Høiland-Jørgensen
2020-04-08 11:53 ` [PATCH RFC v2 30/33] xdp: clear grow memory in bpf_xdp_adjust_tail() Jesper Dangaard Brouer
2020-04-08 21:49 ` David Miller
2020-04-14 9:43 ` Jesper Dangaard Brouer
2020-04-08 11:53 ` [PATCH RFC v2 31/33] bpf: add xdp.frame_sz in bpf_prog_test_run_xdp() Jesper Dangaard Brouer
2020-04-08 11:53 ` [PATCH RFC v2 32/33] selftests/bpf: adjust BPF selftest for xdp_adjust_tail Jesper Dangaard Brouer
2020-04-08 11:53 ` [PATCH RFC v2 33/33] selftests/bpf: xdp_adjust_tail add grow tail tests Jesper Dangaard Brouer
2020-04-08 16:55 ` [PATCH RFC v2 00/33] XDP extend with knowledge of frame size Alexei Starovoitov
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