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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 C2B1AC43382 for ; Tue, 25 Sep 2018 17:56:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7B5F020896 for ; Tue, 25 Sep 2018 17:56:02 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7B5F020896 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727221AbeIZAEj (ORCPT ); Tue, 25 Sep 2018 20:04:39 -0400 Received: from foss.arm.com ([217.140.101.70]:56216 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726304AbeIZAEi (ORCPT ); Tue, 25 Sep 2018 20:04:38 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 03F3118A; Tue, 25 Sep 2018 10:56:00 -0700 (PDT) Received: from [10.4.12.111] (ostrya.Emea.Arm.com [10.4.12.111]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id BA9DC3F5BD; Tue, 25 Sep 2018 10:55:57 -0700 (PDT) Subject: Re: [RFC PATCH v2 08/10] vfio/type1: Add domain at(de)taching group helpers To: "Tian, Kevin" , Lu Baolu , Joerg Roedel , David Woodhouse , Alex Williamson , Kirti Wankhede Cc: "Raj, Ashok" , "Bie, Tiwei" , "Kumar, Sanjay K" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "Sun, Yi Y" , "Pan, Jacob jun" , "kvm@vger.kernel.org" References: <20180830040922.30426-1-baolu.lu@linux.intel.com> <20180830040922.30426-9-baolu.lu@linux.intel.com> <04f5dc9d-71b1-37ec-402b-fae5f9e08664@arm.com> From: Jean-Philippe Brucker Message-ID: <75517c87-6ffd-2023-a541-3c69ae52ef4b@arm.com> Date: Tue, 25 Sep 2018 18:55:41 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/09/2018 00:26, Tian, Kevin wrote: >> If the core actually calls it, we can implement detach_dev :) The >> problem is that the core never calls detach_dev when default_domain is >> present (affects any IOMMU driver that relies on default_domain, >> including AMD), and even in case 4) the default_domain is present for >> the parent device > > Then can we change that core logic so detach_dev is invoked in all > cases? yes there will be some changes in vendor drivers, but I expect > this change trivial (especially considering the gain in IOMMU API > simplicity side as described below). Thinking more about this, there might be a way that doesn't require too much rewriting of IOMMU drivers. When VFIO calls iommu_detach_group to detach a vfio-pci device from its domain, it could do detach_dev(dev, old_domain) followed by attach_dev(dev, default_domain) instead of only attach_dev(dev, default_domain), so: __iommu_attach_group(grp, unmanaged_domain) ops->attach_dev(dev, unmanaged_domain) -> IOMMU driver detaches from default_domain only if the dev isn't in auxiliary mode __iommu_detach_group(grp, unmanaged_domain) if (ops->detach_dev) ops->detach_dev(dev, unmanaged_domain) ops->attach_dev(dev, default_domain) -> IOMMU driver ignores this if still attached to default_domain It's not trivial: since half the IOMMU drivers seem to be using default domain now, their detach_dev callback might have been dead code for a while (I can't find a path where it still gets called), so re-enabling it requires some attention. However, since most of them won't care about aux domains, maybe we could just remove their detach_dev pointer. The resulting logic of attach/detach_dev in IOMMU drivers that do use aux domains still seems unnecessarily convoluted. It could as well be done with separate attach_aux/detach_aux functions. If you want to keep it that way though, I think the above could work for us and I'll try to write an RFC. Thanks, Jean