From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 966FBC432BE for ; Fri, 20 Aug 2021 18:09:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7E00661056 for ; Fri, 20 Aug 2021 18:09:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235976AbhHTSJr (ORCPT ); Fri, 20 Aug 2021 14:09:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:44146 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229560AbhHTSJp (ORCPT ); Fri, 20 Aug 2021 14:09:45 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7787560F11; Fri, 20 Aug 2021 18:09:07 +0000 (UTC) Received: from sofa.misterjones.org ([185.219.108.64] helo=wait-a-minute.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mH8wz-006Ff6-Ej; Fri, 20 Aug 2021 19:09:05 +0100 Date: Fri, 20 Aug 2021 19:09:04 +0100 Message-ID: <87eeaoyon3.wl-maz@kernel.org> From: Marc Zyngier To: Matteo Croce Cc: Eric Dumazet , Thierry Reding , netdev@vger.kernel.org, Linux Kernel Mailing List , linux-riscv , Giuseppe Cavallaro , Alexandre Torgue , "David S. Miller" , Jakub Kicinski , Palmer Dabbelt , Paul Walmsley , Drew Fustini , Emil Renner Berthing , Jon Hunter , Will Deacon Subject: Re: [PATCH net-next] stmmac: align RX buffers In-Reply-To: References: <20210614022504.24458-1-mcroce@linux.microsoft.com> <871r71azjw.wl-maz@kernel.org> <202417ef-f8ae-895d-4d07-1f9f3d89b4a4@gmail.com> <87o8a49idp.wl-maz@kernel.org> <20210812121835.405d2e37@linux.microsoft.com> <874kbuapod.wl-maz@kernel.org> <87wnohqty1.wl-maz@kernel.org> <87fsv4qdzm.wl-maz@kernel.org> <87mtpcyrdv.wl-maz@kernel.org> <87h7fkyqpv.wl-maz@kernel.org> <87fsv4ypfn.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: mcroce@linux.microsoft.com, eric.dumazet@gmail.com, thierry.reding@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, peppe.cavallaro@st.com, alexandre.torgue@foss.st.com, davem@davemloft.net, kuba@kernel.org, palmer@dabbelt.com, paul.walmsley@sifive.com, drew@beagleboard.org, kernel@esmil.dk, jonathanh@nvidia.com, will@kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, 20 Aug 2021 18:56:33 +0100, Matteo Croce wrote: > > On Fri, Aug 20, 2021 at 7:51 PM Marc Zyngier wrote: > > > > On Fri, 20 Aug 2021 18:35:45 +0100, > > Matteo Croce wrote: > > > > > > > > I think it's wrong. The original offset was 0, and to align it to the > > > > > boundary we need to add just NET_IP_ALIGN, which is two. > > > > > NET_SKB_PAD is a much bigger value, (I think 64), which is used to > > > > > reserve space to prepend an header, e.g. with tunnels. > > > > > > > > How about the other adjustments that Eric mentioned regarding the size > > > > of the buffer? Aren't they required? > > > > > > > > > > I guess that if stmmac_rx_buf1_len() needed such adjustment, it would > > > be already broken when XDP is in use. > > > When you use XDP, stmmac_rx_offset() adds a pretty big headroom of 256 > > > byte, which would easily trigger an overflow if not accounted. > > > Did you try attaching a simple XDP program on a stock 5.13 kernel? > > > > Yes, as mentioned in [1], to which you replied... > > > > M. > > > > [1] https://lore.kernel.org/r/87wnohqty1.wl-maz@kernel.org > > > > Great. > So I doubt that the adjustment is needed. > Does it work with all the frame size? I have no idea. Honestly, you are the one who should be able to answer these questions, given that you should have worked out how the buffer allocations work in this particular driver. This whole "let's try another random set of values until something sticks" is not how things ought to be done, and doesn't fill me with the utmost confidence that 5.14 (which apparently may well be cut in *two days*) is going to have a solid stmmac driver. I re-re-request that this patch gets reverted until you figure out what is wrong with the initial patch. Thanks, M. -- Without deviation from the norm, progress is not possible.