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=-10.5 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 0362DC07E96 for ; Thu, 8 Jul 2021 10:18:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE68E61C59 for ; Thu, 8 Jul 2021 10:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231455AbhGHKVe (ORCPT ); Thu, 8 Jul 2021 06:21:34 -0400 Received: from foss.arm.com ([217.140.110.172]:55600 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231372AbhGHKVd (ORCPT ); Thu, 8 Jul 2021 06:21:33 -0400 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 C223CED1; Thu, 8 Jul 2021 03:18:51 -0700 (PDT) Received: from [10.57.35.192] (unknown [10.57.35.192]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E03C63F5A1; Thu, 8 Jul 2021 03:18:50 -0700 (PDT) Subject: Re: [PATCH] iommu/amd: Enable swiotlb if any device supports iommu v2 and uses identity mapping To: Joerg Roedel , Kai-Heng Feng Cc: will@kernel.org, "open list:AMD IOMMU (AMD-VI)" , open list References: <20210708074232.924844-1-kai.heng.feng@canonical.com> From: Robin Murphy Message-ID: Date: Thu, 8 Jul 2021 11:18:45 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-07-08 10:28, Joerg Roedel wrote: > On Thu, Jul 08, 2021 at 03:42:32PM +0800, Kai-Heng Feng wrote: >> @@ -344,6 +344,9 @@ static int iommu_init_device(struct device *dev) >> >> iommu = amd_iommu_rlookup_table[dev_data->devid]; >> dev_data->iommu_v2 = iommu->is_iommu_v2; >> + >> + if (dev_data->iommu_v2) >> + swiotlb = 1; > > This looks like the big hammer, as it will affect all other systems > where the AMD GPUs are in their own group. > > What is needed here is an explicit check whether a non-iommu-v2 device > is direct-mapped because it shares a group with the GPU, and only enable > swiotlb in this case. Right, it's basically about whether any DMA-limited device might at any time end up in an IOMMU_DOMAIN_IDENTITY domain. And given the possibility of device hotplug and the user being silly with the sysfs interface, I don't think we can categorically determine that at boot time. Also note that Intel systems are likely to be similarly affected (in fact intel-iommu doesn't even have the iommu_default_passthough() check so it's probably even easier to blow up). Robin.