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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 3C0BBC32771 for ; Wed, 15 Jan 2020 17:45:14 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 0E8EF24656 for ; Wed, 15 Jan 2020 17:45:13 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E8EF24656 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 185C920773; Wed, 15 Jan 2020 17:45:13 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 7LiDQQUQB2sC; Wed, 15 Jan 2020 17:45:07 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 9E4B420768; Wed, 15 Jan 2020 17:45:07 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 820CCC1D83; Wed, 15 Jan 2020 17:45:07 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 677C5C077D for ; Wed, 15 Jan 2020 17:45:06 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 4A221865D6 for ; Wed, 15 Jan 2020 17:45:06 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Wxr0anPll7Zd for ; Wed, 15 Jan 2020 17:45:01 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by whitealder.osuosl.org (Postfix) with ESMTP id 7A0A38656A for ; Wed, 15 Jan 2020 17:45:01 +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 DBAAA328; Wed, 15 Jan 2020 09:45:00 -0800 (PST) Received: from [10.1.196.37] (e121345-lin.cambridge.arm.com [10.1.196.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E8643F6C4; Wed, 15 Jan 2020 09:44:58 -0800 (PST) Subject: Re: [PATCH v4 11/13] iommu/arm-smmu-v3: Improve add_device() error handling To: Will Deacon , Jean-Philippe Brucker References: <20191219163033.2608177-1-jean-philippe@linaro.org> <20191219163033.2608177-12-jean-philippe@linaro.org> <20200114152538.GB2579@willie-the-truck> From: Robin Murphy Message-ID: <5287c59f-0331-4d2e-e8a0-292bf27683fb@arm.com> Date: Wed, 15 Jan 2020 17:44:57 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200114152538.GB2579@willie-the-truck> Content-Language: en-GB Cc: mark.rutland@arm.com, devicetree@vger.kernel.org, linux-pci@vger.kernel.org, sudeep.holla@arm.com, rjw@rjwysocki.net, linux-acpi@vger.kernel.org, iommu@lists.linux-foundation.org, robh+dt@kernel.org, guohanjun@huawei.com, bhelgaas@google.com, zhangfei.gao@linaro.org, linux-arm-kernel@lists.infradead.org, lenb@kernel.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On 14/01/2020 3:25 pm, Will Deacon wrote: > On Thu, Dec 19, 2019 at 05:30:31PM +0100, Jean-Philippe Brucker wrote: >> Let add_device() clean up after itself. The iommu_bus_init() function >> does call remove_device() on error, but other sites (e.g. of_iommu) do >> not. >> >> Don't free level-2 stream tables because we'd have to track if we >> allocated each of them or if they are used by other endpoints. It's not >> worth the hassle since they are managed resources. >> >> Reviewed-by: Eric Auger >> Reviewed-by: Jonathan Cameron >> Signed-off-by: Jean-Philippe Brucker >> --- >> drivers/iommu/arm-smmu-v3.c | 28 +++++++++++++++++++++------- >> 1 file changed, 21 insertions(+), 7 deletions(-) > > I think this is alright, with one caveat relating to: > > > /* > * We _can_ actually withstand dodgy bus code re-calling add_device() > * without an intervening remove_device()/of_xlate() sequence, but > * we're not going to do so quietly... > */ > if (WARN_ON_ONCE(fwspec->iommu_priv)) { > master = fwspec->iommu_priv; > smmu = master->smmu; > } ... > > > which may be on shakey ground if the subsequent add_device() call can fail > and free stuff that the first one allocated. At least, I don't know what > we're trying to support with this, so it's hard to tell whether or not it > still works as intended after your change. Hmm, if add_device() ever did fail it should really be expected to return the device back to an un-added state, so I don't believe that particular concern should be significant regardless... > How is this supposed to work? I don't recall ever seeing that WARN fire, > so can we just remove this and bail instead? Robin? However, I am inclined to agree that it's probably better to make it all moot. Although it indeed should never happen, ISTR at the time there appeared to be some possible path somewhere by which the notifier may have been triggered a second time - possibly if some other device failed or deferred after the first call, triggering the bus code to start all over again. Since then, though, we've made a lot of changes to how ->add_device usually gets called, plus stuff like the iommu_device_link() call has snuck in that might not stand up to a replay anyway, so I don't see any problem with making this condition a hard failure. It's certainly much easier to reason about. In fact, there will already be a WARN from iommu_probe_device() now (because the first call will have set the group), so I don't think we need any additional diagnostic in the driver any more. Robin. > Something like below before your changes... > > Will > > --->8 > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > index effe72eb89e7..6ae3df2f3495 100644 > --- a/drivers/iommu/arm-smmu-v3.c > +++ b/drivers/iommu/arm-smmu-v3.c > @@ -2534,28 +2534,23 @@ static int arm_smmu_add_device(struct device *dev) > > if (!fwspec || fwspec->ops != &arm_smmu_ops) > return -ENODEV; > - /* > - * We _can_ actually withstand dodgy bus code re-calling add_device() > - * without an intervening remove_device()/of_xlate() sequence, but > - * we're not going to do so quietly... > - */ > - if (WARN_ON_ONCE(fwspec->iommu_priv)) { > - master = fwspec->iommu_priv; > - smmu = master->smmu; > - } else { > - smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode); > - if (!smmu) > - return -ENODEV; > - master = kzalloc(sizeof(*master), GFP_KERNEL); > - if (!master) > - return -ENOMEM; > > - master->dev = dev; > - master->smmu = smmu; > - master->sids = fwspec->ids; > - master->num_sids = fwspec->num_ids; > - fwspec->iommu_priv = master; > - } > + if (WARN_ON_ONCE(fwspec->iommu_priv)) > + return -EBUSY; > + > + smmu = arm_smmu_get_by_fwnode(fwspec->iommu_fwnode); > + if (!smmu) > + return -ENODEV; > + > + master = kzalloc(sizeof(*master), GFP_KERNEL); > + if (!master) > + return -ENOMEM; > + > + master->dev = dev; > + master->smmu = smmu; > + master->sids = fwspec->ids; > + master->num_sids = fwspec->num_ids; > + fwspec->iommu_priv = master; > > /* Check the SIDs are in range of the SMMU and our stream table */ > for (i = 0; i < master->num_sids; i++) { > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu