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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 68A14C433E2 for ; Fri, 29 May 2020 21:21:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42C3F20776 for ; Fri, 29 May 2020 21:21:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=deltatee.com header.i=@deltatee.com header.b="b96g+2M4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728297AbgE2VVe (ORCPT ); Fri, 29 May 2020 17:21:34 -0400 Received: from ts18-13.vcr.istar.ca ([204.191.154.188]:57946 "EHLO ale.deltatee.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1727879AbgE2VVe (ORCPT ); Fri, 29 May 2020 17:21:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=deltatee.com; s=20200525; h=Subject:Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Sender: Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender :Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=fj4wKOtVYLrcqYVXpt9c2vH51FUvKotCgqQuY7zVZ2k=; b=b96g+2M4iyp1SAYrzZS1fpiUCq ePzANrhF0COO+6jRUPoeDmySlgJVU6m/rPyXt57P4RCIonCpkajDWlESxSns8SkeMf1JUN+p5VwXI LaIpyCsQ3xEY1tRZbmrAX1IIBtYPv/hiJXGWo2BfT5aPumyg7CKRMqnBzpal97YO+lQtoBA8ZuQUK SvJ/HICeFgy28c6+YAi2NJ+GFJ1XPggoZqdjJjDjetSllwedUe6OueW8gHeiWxj/co4q2lewqWPGz DL15eKFLSm2BXN06PzSHNqzjDuDvbEQNIY7M7rCSGRrH1HOWFDVmuFoq8SLMVZEdPWs3RbLgauKc/ 5xPZm2ZA==; Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.92) (envelope-from ) id 1jemRE-0004yn-1k; Fri, 29 May 2020 15:21:12 -0600 To: Marek Szyprowski , Christoph Hellwig Cc: Tom Murphy , iommu@lists.linux-foundation.org, kvm@vger.kernel.org, David Airlie , dri-devel@lists.freedesktop.org, Bjorn Andersson , Matthias Brugger , Julien Grall , Thierry Reding , Will Deacon , Jean-Philippe Brucker , linux-samsung-soc@vger.kernel.org, Marc Zyngier , Krzysztof Kozlowski , Jonathan Hunter , linux-rockchip@lists.infradead.org, Andy Gross , Gerald Schaefer , linux-s390@vger.kernel.org, linux-arm-msm@vger.kernel.org, intel-gfx@lists.freedesktop.org, Alex Williamson , linux-mediatek@lists.infradead.org, Rodrigo Vivi , linux-tegra@vger.kernel.org, Thomas Gleixner , virtualization@lists.linux-foundation.org, linux-arm-kernel@lists.infradead.org, Robin Murphy , Cornelia Huck , linux-kernel@vger.kernel.org, Kukjin Kim , David Woodhouse , Jani Nikula , Joonas Lahtinen References: <20191221150402.13868-1-murphyt7@tcd.ie> <465815ae-9292-f37a-59b9-03949cb68460@deltatee.com> <20200529124523.GA11817@infradead.org> <33137cfb-603c-86e8-1091-f36117ecfaf3@deltatee.com> From: Logan Gunthorpe Message-ID: Date: Fri, 29 May 2020 15:21:04 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: joonas.lahtinen@linux.intel.com, jani.nikula@linux.intel.com, dwmw2@infradead.org, kgene@kernel.org, linux-kernel@vger.kernel.org, cohuck@redhat.com, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org, virtualization@lists.linux-foundation.org, tglx@linutronix.de, linux-tegra@vger.kernel.org, rodrigo.vivi@intel.com, linux-mediatek@lists.infradead.org, alex.williamson@redhat.com, intel-gfx@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, linux-s390@vger.kernel.org, gerald.schaefer@de.ibm.com, agross@kernel.org, linux-rockchip@lists.infradead.org, jonathanh@nvidia.com, krzk@kernel.org, maz@kernel.org, linux-samsung-soc@vger.kernel.org, jean-philippe@linaro.org, will@kernel.org, thierry.reding@gmail.com, julien.grall@arm.com, matthias.bgg@gmail.com, bjorn.andersson@linaro.org, dri-devel@lists.freedesktop.org, airlied@linux.ie, kvm@vger.kernel.org, iommu@lists.linux-foundation.org, murphyt7@tcd.ie, hch@infradead.org, m.szyprowski@samsung.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-samsung-soc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-samsung-soc@vger.kernel.org On 2020-05-29 3:11 p.m., Marek Szyprowski wrote: > Patches are pending: > https://lore.kernel.org/linux-iommu/20200513132114.6046-1-m.szyprowski@samsung.com/T/ Cool, nice! Though, I still don't think that fixes the issue in i915_scatterlist.h given it still ignores sg_dma_len() and strictly relies on sg_next()/sg_is_last() to stop iterating -- and I suspect this is the bug that got in Tom's way. >> However, as Robin pointed out, there are other ugly tricks like stopping >> iterating through the SGL when sg_dma_len() is zero. For example, the >> AMD driver appears to use drm_prime_sg_to_page_addr_arrays() which does >> this trick and thus likely isn't buggy (otherwise, I'd expect someone to >> have complained by now seeing AMD has already switched to IOMMU-DMA. > > I'm not sure that this is a trick. Stopping at zero sg_dma_len() was > somewhere documented. Well whatever you want to call it, it is ugly to have some drivers doing one thing with the returned value and others assuming there's an extra zero at the end. It just causes confusion for people reading/copying the code. It would be better if they are all consistent. However, I concede stopping at zero should not be broken, presently. Logan