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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 1CA23C636CA for ; Fri, 16 Jul 2021 12:19:46 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id D38226128B for ; Fri, 16 Jul 2021 12:19:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D38226128B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.157152.290059 (Exim 4.92) (envelope-from ) id 1m4MoY-0007lZ-6N; Fri, 16 Jul 2021 12:19:34 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 157152.290059; Fri, 16 Jul 2021 12:19:34 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m4MoY-0007lS-3N; Fri, 16 Jul 2021 12:19:34 +0000 Received: by outflank-mailman (input) for mailman id 157152; Fri, 16 Jul 2021 12:19:32 +0000 Received: from us1-rack-iad1.inumbo.com ([172.99.69.81]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1m4MoW-0007lM-Ni for xen-devel@lists.xenproject.org; Fri, 16 Jul 2021 12:19:32 +0000 Received: from foss.arm.com (unknown [217.140.110.172]) by us1-rack-iad1.inumbo.com (Halon) with ESMTP id d3373b79-8114-44fe-951f-3b05d3e96735; Fri, 16 Jul 2021 12:19:31 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 08358D6E; Fri, 16 Jul 2021 05:19:31 -0700 (PDT) Received: from [10.57.36.240] (unknown [10.57.36.240]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BF0533F774; Fri, 16 Jul 2021 05:19:28 -0700 (PDT) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d3373b79-8114-44fe-951f-3b05d3e96735 Subject: Re: [PATCH v1 16/16] dma-mapping: Disallow .map_sg operations from returning zero on error To: Christoph Hellwig , Logan Gunthorpe Cc: linux-s390@vger.kernel.org, linux-ia64@vger.kernel.org, linux-parisc@vger.kernel.org, Martin Oliveira , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, linux-alpha@vger.kernel.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, Stephen Bates , linuxppc-dev@lists.ozlabs.org, linux-arm-kernel@lists.infradead.org References: <20210715164544.6827-1-logang@deltatee.com> <20210715164544.6827-17-logang@deltatee.com> <20210716063332.GD13345@lst.de> From: Robin Murphy Message-ID: <21b7f2f1-ccac-4567-6933-a258dcad7099@arm.com> Date: Fri, 16 Jul 2021 13:19:23 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210716063332.GD13345@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit On 2021-07-16 07:33, Christoph Hellwig wrote: > On Thu, Jul 15, 2021 at 10:45:44AM -0600, Logan Gunthorpe wrote: >> @@ -194,6 +194,8 @@ static int __dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, >> else >> ents = ops->map_sg(dev, sg, nents, dir, attrs); >> >> + WARN_ON_ONCE(ents == 0); > > Turns this into a negative error code while we're at it, just to keep > the callers sane? Right, by this point returning the 0 would pass through dma_map_sg_attrs() OK, but AFAICS dma_map_sgtable() would now get confused and return success but with sgt->nents = 0. Coercing it to an error code (which dma_map_sg_attrs() would then just change right back) seems sensible for the sake of easy robustness. Robin.