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Miller'" , "'Jakub Kicinski'" , "'Network Development'" , "'linux-kernel'" In-Reply-To: Subject: RE: [PATCH bpf] bpf: check for data_len before upgrading mss when 6 to 4 Date: Wed, 12 May 2021 09:45:03 +0900 Message-ID: <01b701d746c8$0c15ae70$24410b50$@samsung.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Mailer: Microsoft Outlook 16.0 Thread-Index: AQKypHYW3xad5/j2XvChPebQmKG2owG+YoocAqFpyMsBZavlXQIxNaIYAiru3ucBq8RF2QKY6vTDAm6kVlUBadK04AMaqQ3GARiLayQDE+caWwJJGwtFAeZKb9QDLW923AHUONYWAfw9g6SoAqstYA== Content-Language: ko X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFjrKJsWRmVeSWpSXmKPExsWy7bCmma6A6uwEg43TzSy+/57NbPHl5212 i89HjrNZLF74jdlizvkWFoumHSuYLF58eMJo8XxfL5PFhW19rBaXd81hs2h4y2VxbIGYxc/D Z5gtFv/cAFS1ZAajA7/HlpU3mTwmNr9j99g56y67R8uRt6weXTcuMXtsWtXJ5vF5k1wAe1SO TUZqYkpqkUJqXnJ+SmZeuq2Sd3C8c7ypmYGhrqGlhbmSQl5ibqqtkotPgK5bZg7Q2UoKZYk5 pUChgMTiYiV9O5ui/NKSVIWM/OISW6XUgpScAkPDAr3ixNzi0rx0veT8XCtDAwMjU6DKhJyM CdMOsRScF6z4eyuxgXE9bxcjJ4eEgInE5F1PmEFsIYEdjBLzb/l0MXIB2Z8YJf6v3sAC4Xxj lNh7q48JpqNryis2iI69jBITbhRBFL1glDh0bhJYEZuAlsSbWe2sILaIgJXE/9kn2EGKmAVO s0g8Wf0NrIhTIFBic98BsCJhgWCJp5OawOIsAqoSS3tBVnNy8ApYSvzbNJsJwhaUODnzCVic WUBeYvvbOcwQFylI/Hy6jBVkgYjAMkaJaX+nMUIUiUjM7myDKnrAIbHoiRGE7SJxecJ1dghb WOLV8S1QtpTE53d7gV7jALLrJVq7Y0BmSgj0MEpc2QexWELAWGLWs3ZGkBpmAU2J9bv0IcqV JY7cgjqNT6Lj8F92iDCvREebEISpJDHxSzzEDAmJFycns0xgVJqF5K9ZSP6aheT8WQirFjCy rGIUSy0ozk1PLTYqMEaO6U2M4PSs5b6DccbbD3qHGJk4GA8xSnAwK4nwzq2flSDEm5JYWZVa lB9fVJqTWnyI0RQY0hOZpUST84EZIq8k3tDUyMzMwNLUwtTMyEJJnPdnal2CkEB6Yklqdmpq QWoRTB8TB6dUA1N9Ln/Gh6fXjetYd/SUnNz3nUtY1u+F9hx3V0mThhOMW97f28Nq1l/5dXkp J+supxfJJ5XmHpO9EaYRVTvFTsZ77Zar7N+myF5xLroYPu2J0/3VT/7Ob6m76vvGVKrMXtmj N6J+SvwL39crnrcJ7I/buPBu9wL7rNu/C0X/Tt/D536I7ebvuNeLpsjZf4v0Z+r55mNfflEv 271tcaz23sCIa285m/YIsRtJabz22/Q+9XDKm9iC1VYfLqVbtGoaiHkdWuj88P+PFGUWzZ2p 11UNuKOO8ZX/6Oa/8Iypa9JuVofy2Uma3rn/Fx3tL/GImvxr8ymlCnFZo6QnDI8ULUU6OT+u FhecO1Vyqkb6OyWW4oxEQy3mouJEAKIla6xYBAAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrCIsWRmVeSWpSXmKPExsWy7bCSnK6A6uwEgzUHuCy+/57NbPHl5212 i89HjrNZLF74jdlizvkWFoumHSuYLF58eMJo8XxfL5PFhW19rBaXd81hs2h4y2VxbIGYxc/D Z5gtFv/cAFS1ZAajA7/HlpU3mTwmNr9j99g56y67R8uRt6weXTcuMXtsWtXJ5vF5k1wAexSX TUpqTmZZapG+XQJXxoRph1gKzgtW/L2V2MC4nreLkZNDQsBEomvKK7YuRi4OIYHdjBLTT+0F cjiAEhISuza7QtQIS9xvOcIKUfOMUeLj76csIAk2AS2JN7PaWUFsEQErif+zT7CDFDELXGWR 2PzjGzNExz4OiQsn3zCBVHEKBEps7jsA1iEMZPf/u8UIYrMIqEos7d0ANpVXwFLi36bZTBC2 oMTJmU/A4swC2hK9D1sZIWx5ie1v5zBDnKcg8fPpMrDzRASWMUpM+zsNqkhEYnZnG/MERuFZ SGbNQjJrFpJZs5C0LGBkWcUomVpQnJueW2xYYJiXWq5XnJhbXJqXrpecn7uJERyxWpo7GLev +qB3iJGJg/EQowQHs5II79z6WQlCvCmJlVWpRfnxRaU5qcWHGKU5WJTEeS90nYwXEkhPLEnN Tk0tSC2CyTJxcEo1MLWpmM/aENMXZ55f5eKU9r+wrWXjEaOaEz+8e1I3Vy+zdlws1bbkh+Pj 4yk51+o7fkvUMMx7uzVdQTdaVlKZJ8Xqbu3Jtl/Tzhy5pvTv5cfgC88erBe88MxiwVqmc9cS v95+HF91Vqq3y2NOYcH1f3Y9Gvef7Jv4/RxjU9bDv7Lue/5aW094EWrMsTV/+nLRHTtfLgxO 6fr26GQX0wZphUMzzp9ZIFzyvk+lqnTj1fmFcy+WdTxnDJ4VIuv233yDn2jGu8iz+nMeTLnw d2bUfJV6uf1Zli2O1Z8E5/5P+PpDQG71kc9bVoWH2oZOX/D7+M9lB84zq/LN2ud5zOfJjXZZ 14nmp6tf6wZX/Xy8VKdeiaU4I9FQi7moOBEAVTXzjEcDAAA= X-CMS-MailID: 20210512004504epcas2p3e3dc9b5dc5df6ea16fb887e0fb23718c X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" X-Sendblock-Type: AUTO_CONFIDENTIAL CMS-TYPE: 102P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20210429102143epcas2p4c8747c09a9de28f003c20389c050394a References: <1619690903-1138-1-git-send-email-dseok.yi@samsung.com> <8c2ea41a-3fc5-d560-16e5-bf706949d857@iogearbox.net> <02bf01d74211$0ff4aed0$2fde0c70$@samsung.com> <02c801d7421f$65287a90$2f796fb0$@samsung.com> <001801d742db$68ab8060$3a028120$@samsung.com> <436dbc62-451b-9b29-178d-9da28f47ef24@huawei.com> <007001d7431a$96281960$c2784c20$@samsung.com> <00c901d74543$57fa3620$07eea260$@samsung.com> <015101d74602$86442210$92cc6630$ @samsung.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 11, 2021 at 01:38:41PM -0400, Willem de Bruijn wrote: > On Mon, May 10, 2021 at 9:11 PM Dongseok Yi wrote: > > > > On Mon, May 10, 2021 at 09:46:25AM -0400, Willem de Bruijn wrote: > > > On Mon, May 10, 2021 at 9:19 AM Willem de Bruijn > > > wrote: > > > > > > > > > > That generates TCP packets with different MSS within the same stream. > > > > > > > > > > > > My suggestion remains to just not change MSS at all. But this has to > > > > > > be a new flag to avoid changing established behavior. > > > > > > > > > > I don't understand why the mss size should be kept in GSO step. Will > > > > > there be any issue with different mss? > > > > > > > > This issue has come up before and that has been the feedback from > > > > TCP experts at one point. > > > > > > > > > In general, upgrading mss make sense when 6 to 4. The new flag would be > > > > > set by user to not change mss. What happened if user does not set the > > > > > flag? I still think we should fix the issue with a general approach. Or > > > > > can we remove the skb_increase_gso_size line? > > > > > > > > Admins that insert such BPF packets should be aware of these issues. > > > > And likely be using clamping. This is a known issue. > > > > > > > > We arrived that the flag approach in bpf_skb_net_shrink. Extending > > > > that to bpf_skb_change_proto would be consistent. > > > > > > As for more generic approach: does downgrading to non-TSO by clearing > > > gso_size work for this edge case? > > > > It can hit __skb_linearize in validate_xmit_skb and frags will be > > copied to a linear part. The linear part size can exceed the MTU of > > skb->dev unexpectedly. > > When does skb_needs_linearize return true here (besides lack of > scatter-gather support, which would also preclude TSO)? As I know not every netdev support NETIF_F_SG. TSO requires SG. /* TSO requires that SG is present as well. */ if ((features & NETIF_F_ALL_TSO) && !(features & NETIF_F_SG)) { netdev_dbg(dev, "Dropping TSO features since no SG feature.\n"); features &= ~NETIF_F_ALL_TSO; } > > > I will make another patch with the flag approach. > >