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=-2.2 required=3.0 tests=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 64A38C2D0CE for ; Tue, 21 Jan 2020 12:45:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3D30C24653 for ; Tue, 21 Jan 2020 12:45:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729673AbgAUMpM (ORCPT ); Tue, 21 Jan 2020 07:45:12 -0500 Received: from foss.arm.com ([217.140.110.172]:42812 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727350AbgAUMpM (ORCPT ); Tue, 21 Jan 2020 07:45:12 -0500 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 370E730E; Tue, 21 Jan 2020 04:45:11 -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 D3F8B3F6C4; Tue, 21 Jan 2020 04:45:09 -0800 (PST) Subject: Re: [RFC PATCH 3/4] iommu: Preallocate iommu group when probing devices To: Lu Baolu , Joerg Roedel Cc: Greg Kroah-Hartman , Bjorn Helgaas , ashok.raj@intel.com, jacob.jun.pan@intel.com, kevin.tian@intel.com, Christoph Hellwig , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20200101052648.14295-1-baolu.lu@linux.intel.com> <20200101052648.14295-4-baolu.lu@linux.intel.com> <20200117102151.GF15760@8bytes.org> <25e2e7fa-487c-f951-4b2c-27bac5e30815@linux.intel.com> From: Robin Murphy Message-ID: Date: Tue, 21 Jan 2020 12:45:08 +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: <25e2e7fa-487c-f951-4b2c-27bac5e30815@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/01/2020 6:29 am, Lu Baolu wrote: > Hi Joerg, > > On 1/17/20 6:21 PM, Joerg Roedel wrote: >> On Wed, Jan 01, 2020 at 01:26:47PM +0800, Lu Baolu wrote: >>> This splits iommu group allocation from adding devices. This makes >>> it possible to determine the default domain type for each group as >>> all devices belonging to the group have been determined. >> >> I think its better to keep group allocation as it is and just defer >> default domain allocation after each device is in its group. But take > > I tried defering default domain allocation, but it seems not possible. > > The call path of adding devices into their groups: > > iommu_probe_device > -> ops->add_device(dev) >    -> (iommu vendor driver) iommu_group_get_for_dev(dev) > > After doing this, the vendor driver will get the default domain and > apply dma_ops according to the domain type. If we defer the domain > allocation, they will get a NULL default domain and cause panic in > the vendor driver. > > Any suggestions? https://lore.kernel.org/linux-iommu/6dbbfc10-3247-744c-ae8d-443a336e0c50@linux.intel.com/ Haven't we been here before? ;) Since we can't (safely or reasonably) change a group's default domain after ops->add_device() has returned, and in general it gets impractical to evaluate "all device in a group" once you look beyond &pci_bus_type (or consider hotplug as mentioned), then AFAICS there's no reasonable way to get away from the default domain type being defined by the first device to attach. But in practice it's hardly a problem anyway - if every device in a given group requests the same domain type then it doesn't matter which comes first, and if they don't then we ultimately end up with an impossible set of constraints, so are doomed to do the 'wrong' thing regardless. Thus unless anyone wants to start redefining the whole group concept to separate the notions of ID aliasing and peer-to-peer isolation (which still wouldn't necessarily help), I think this user override effectively boils down to just another flavour of iommu_request_*_for_dev(), and as such comes right back to the "just pass the bloody device to ops->domain_alloc() and resolve everything up-front" argument. Robin.