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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 359BAC4320A for ; Fri, 20 Aug 2021 17:09:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1B9A86113E for ; Fri, 20 Aug 2021 17:09:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232789AbhHTRK3 (ORCPT ); Fri, 20 Aug 2021 13:10:29 -0400 Received: from mail.kernel.org ([198.145.29.99]:45088 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230052AbhHTRK1 (ORCPT ); Fri, 20 Aug 2021 13:10:27 -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 4CADF610CC; Fri, 20 Aug 2021 17:09:49 +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 1mH81b-006F6e-9Z; Fri, 20 Aug 2021 18:09:47 +0100 Date: Fri, 20 Aug 2021 18:09:48 +0100 Message-ID: <87mtpcyrdv.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> 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: linux-kernel@vger.kernel.org On Fri, 20 Aug 2021 17:38:14 +0100, Matteo Croce wrote: > > On Fri, Aug 20, 2021 at 6:26 PM Marc Zyngier wrote: > > > > On Fri, 20 Aug 2021 11:37:03 +0100, > > Matteo Croce wrote: > > > > > > On Thu, Aug 19, 2021 at 6:29 PM Marc Zyngier wrote: > > > > [...] > > > > > > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac.h b/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > index fcdb1d20389b..244aa6579ef4 100644 > > > > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac.h > > > > @@ -341,7 +341,7 @@ static inline unsigned int stmmac_rx_offset(struct stmmac_priv *priv) > > > > if (stmmac_xdp_is_enabled(priv)) > > > > return XDP_PACKET_HEADROOM + NET_IP_ALIGN; > > > > > > > > - return NET_SKB_PAD + NET_IP_ALIGN; > > > > + return 8 + NET_IP_ALIGN; > > > > } > > > > > > > > void stmmac_disable_rx_queue(struct stmmac_priv *priv, u32 queue); > > > > > > > > I don't see the system corrupting packets anymore. Is that exactly > > > > what you had in mind? This really seems to point to a basic buffer > > > > overflow. > > > > [...] > > > > > Sorry, I meant something like: > > > > > > - return NET_SKB_PAD + NET_IP_ALIGN; > > > + return 8; > > > > > > I had some hardware which DMA fails if the receive buffer was not word > > > aligned, but this seems not the case, as 8 + NET_IP_ALIGN = 10, and > > > it's not aligned too. > > > > No error in that case either, as expected. Given that NET_SKB_PAD is > > likely to expand to 64, it is likely a DMA buffer overflow which > > probably only triggers for large-ish packets. > > > > Now, we're almost at -rc7, and we don't have a solution in sight. > > > > Can we please revert this until we have an understanding of what is > > happening? I'll hopefully have more cycles to work on the issue once > > 5.14 is out, and hopefully the maintainers of this driver can chime in > > (they have been pretty quiet so far). > > > > Thanks, > > > > M. > > > > -- > > Without deviation from the norm, progress is not possible. > > Last try, what about adding only NET_IP_ALIGN and leaving NET_SKB_PAD? > > - return NET_SKB_PAD + NET_IP_ALIGN; > + return NET_IP_ALIGN; > > I think that alloc_skb adds another NET_SKB_PAD anyway. I don't see any packet corruption with this. However, this doesn't prove that this is correct either. What was the rational for adding NET_SKB_PAD the first place? M. -- Without deviation from the norm, progress is not possible.