Re: [PATCH net v2] veth: xdp: use head instead of hard_start

From: Jesper Dangaard Brouer <brouer@redhat.com>
To: Toshiaki Makita <toshiaki.makita1@gmail.com>
Cc: Mao Wenan <maowenan@huawei.com>,
	davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net,
	kuba@kernel.org, hawk@kernel.org, john.fastabend@gmail.com,
	kafai@fb.com, songliubraving@fb.com, yhs@fb.com, andriin@fb.com,
	jwi@linux.ibm.com, jianglidong3@jd.com, edumazet@google.com,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org, kernel-janitors@vger.kernel.org,
	brouer@redhat.com
Subject: Re: [PATCH net v2] veth: xdp: use head instead of hard_start
Date: Thu, 2 Apr 2020 11:06:19 +0200	[thread overview]
Message-ID: <20200402110619.48f31a63@carbon> (raw)
In-Reply-To: <ede2f407-839e-d29e-0ebe-aa39dd461bfd@gmail.com>

On Thu, 2 Apr 2020 09:47:03 +0900
Toshiaki Makita <toshiaki.makita1@gmail.com> wrote:

> On 2020/04/02 1:15, Jesper Dangaard Brouer wrote:
> ...
> > [PATCH RFC net-next] veth: adjust hard_start offset on redirect XDP frames
> > 
> > When native XDP redirect into a veth device, the frame arrives in the
> > xdp_frame structure. It is then processed in veth_xdp_rcv_one(),
> > which can run a new XDP bpf_prog on the packet. Doing so requires
> > converting xdp_frame to xdp_buff, but the tricky part is that
> > xdp_frame memory area is located in the top (data_hard_start) memory
> > area that xdp_buff will point into.
> > 
> > The current code tried to protect the xdp_frame area, by assigning
> > xdp_buff.data_hard_start past this memory. This results in 32 bytes
> > less headroom to expand into via BPF-helper bpf_xdp_adjust_head().
> > 
> > This protect step is actually not needed, because BPF-helper
> > bpf_xdp_adjust_head() already reserve this area, and don't allow
> > BPF-prog to expand into it. Thus, it is safe to point data_hard_start
> > directly at xdp_frame memory area.
> > 
> > Cc: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>  
> 
> FYI: This mail address is deprecated.
> 
> > Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring")
> > Reported-by: Mao Wenan <maowenan@huawei.com>
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>  
> 
> FWIW,
> 
> Acked-by: Toshiaki Makita <toshiaki.makita1@gmail.com>

Thanks.

I have updated your email and added your ack in my patchset.  I will
submit this officially once net-next opens up again[1], as part my
larger patchset for introducing XDP frame_sz.

[1] http://vger.kernel.org/~davem/net-next.html
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer