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,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 1159EC433F5 for ; Tue, 7 Sep 2021 07:42:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E89D6610A3 for ; Tue, 7 Sep 2021 07:42:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242346AbhIGHoD (ORCPT ); Tue, 7 Sep 2021 03:44:03 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:9009 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240450AbhIGHnM (ORCPT ); Tue, 7 Sep 2021 03:43:12 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4H3cdk19QvzVqZY; Tue, 7 Sep 2021 15:41:14 +0800 (CST) Received: from dggema765-chm.china.huawei.com (10.1.198.207) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2308.8; Tue, 7 Sep 2021 15:42:04 +0800 Received: from [10.174.185.210] (10.174.185.210) by dggema765-chm.china.huawei.com (10.1.198.207) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2308.8; Tue, 7 Sep 2021 15:42:03 +0800 From: Kunkun Jiang Subject: [question] Assign multiple devices from different SMMUs to a arm_smmu_domain To: Robin Murphy , Will Deacon , "Linux IOMMU" , open list CC: , Zenghui Yu , "Keqian Zhu" Message-ID: Date: Tue, 7 Sep 2021 15:41:52 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Originating-IP: [10.174.185.210] X-ClientProxiedBy: dggeme701-chm.china.huawei.com (10.1.199.97) To dggema765-chm.china.huawei.com (10.1.198.207) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, I am working on VFIO DMA dirty pages tracking based on ARM SMMU HTTU, and have done a lot of testing.In the test, I found a problem that greatly affects performance of VFIO DMA dirty pages tracking. According to the current arm-smmu-v3 driver, multiple VFIO pass-through device comes from different SMMUs will be assigned to different arm_smmu_domain. It will create page table for each arm_smmu_domain, even though these page tables are exactly the same. Bacause dirty pages tracking needs to traverse the page table, multiple page tables will make performance worse. I learned the ARM SMMUv3 spec and had some exchanges with my colleagues who work on SMMU hardware. I did not find the restriction that multiple SMMUs cannot share the same page table. We migth be able to do this like x86 IOMMU. If I have missed something, please point it out. Looking forward to your suggestions.😁 Thanks, Kunkun Jiang