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[223.218.245.204]) by smtp.googlemail.com with ESMTPSA id 63sm2451755pfx.132.2020.04.01.17.47.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 01 Apr 2020 17:47:08 -0700 (PDT) Subject: Re: [PATCH net v2] veth: xdp: use head instead of hard_start To: Jesper Dangaard Brouer Cc: Mao Wenan , 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 References: <20200331060641.79999-1-maowenan@huawei.com> <7a1d55ad-1427-67fe-f204-4d4a0ab2c4b1@gmail.com> <20200401181419.7acd2aa6@carbon> From: Toshiaki Makita Message-ID: Date: Thu, 2 Apr 2020 09:47:03 +0900 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200401181419.7acd2aa6@carbon> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org 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 FYI: This mail address is deprecated. > Fixes: 9fc8d518d9d5 ("veth: Handle xdp_frames in xdp napi ring") > Reported-by: Mao Wenan > Signed-off-by: Jesper Dangaard Brouer FWIW, Acked-by: Toshiaki Makita