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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 C6F81C433B4 for ; Wed, 14 Apr 2021 17:47:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FEDE61042 for ; Wed, 14 Apr 2021 17:47:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347383AbhDNRsC (ORCPT ); Wed, 14 Apr 2021 13:48:02 -0400 Received: from frasgout.his.huawei.com ([185.176.79.56]:2857 "EHLO frasgout.his.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234304AbhDNRr5 (ORCPT ); Wed, 14 Apr 2021 13:47:57 -0400 Received: from fraeml738-chm.china.huawei.com (unknown [172.18.147.226]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4FL8nJ6kwxz6898S; Thu, 15 Apr 2021 01:37:40 +0800 (CST) Received: from lhreml724-chm.china.huawei.com (10.201.108.75) by fraeml738-chm.china.huawei.com (10.206.15.219) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Wed, 14 Apr 2021 19:47:33 +0200 Received: from [10.47.25.158] (10.47.25.158) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2106.2; Wed, 14 Apr 2021 18:47:32 +0100 From: John Garry Subject: Re: [PATCH 1/6] iommu: Move IOVA power-of-2 roundup into allocator To: Robin Murphy , "joro@8bytes.org" , "will@kernel.org" , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "hch@lst.de" , "m.szyprowski@samsung.com" CC: "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "linux-scsi@vger.kernel.org" , Linuxarm References: <1616160348-29451-1-git-send-email-john.garry@huawei.com> <1616160348-29451-2-git-send-email-john.garry@huawei.com> <73d459de-b5cc-e2f5-bcd7-2ee23c8d5075@huawei.com> <08c0f4b9-8713-fa97-3986-3cfb0d6b820b@huawei.com> <4914d134-5a63-f683-b14b-25ab71a57cd4@huawei.com> Message-ID: <8fce915b-18fa-2bfb-66d7-325cb7837894@huawei.com> Date: Wed, 14 Apr 2021 18:44:58 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <4914d134-5a63-f683-b14b-25ab71a57cd4@huawei.com> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.47.25.158] X-ClientProxiedBy: lhreml730-chm.china.huawei.com (10.201.108.81) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/04/2021 17:54, John Garry wrote: Hi Robin, > >> Sorry if the phrasing was unclear there - the allusion to default >> domains is new, it just occurred to me that what we do there is in >> fact fairly close to what I've suggested previously for this. In that >> case, we have a global policy set by the command line, which *can* be >> overridden per-domain via sysfs at runtime, provided the user is >> willing to tear the whole thing down. Using a similar approach here >> would give a fair degree of flexibility but still mean that changes >> never have to be made dynamically to a live domain. > > So are you saying that we can handle it similar to how we now can handle > changing default domain for an IOMMU group via sysfs? If so, that just > is not practical here. Reason being that this particular DMA engine > provides the block device giving / mount point, so if we unbind the > driver, we lose / mount point. > > And I am not sure if the end user would even know how to set such a > tunable. Or, in this case, why the end user would not want the optimized > range configured always. > > I'd still rather if the device driver could provide info which can be > used to configure this before or during probing. As a new solution, how about do both of these: a. Add a per-IOMMU group sysfs file to set this tunable. Works same as how we change the default domain, and has all the same restrictions/steps. I think that this is what you are already suggesting. b. Provide a DMA mapping API to set this value, similar to this current series. In the IOMMU backend for that API, we record a new range value and return -EPROBE_DEFER when successful. In the reprobe we reset the default domain for the devices' IOMMU group, with the IOVA domain rcache range configured as previously requested. Again, allocating the new default domain is similar to how we change default domain type today. This means that we don't play with a live domain. Downside is that we need to defer the probe. Thanks, John