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 95EDEC4361A for ; Mon, 19 Apr 2021 13:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 71BB861284 for ; Mon, 19 Apr 2021 13:40:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243234AbhDSNkS (ORCPT ); Mon, 19 Apr 2021 09:40:18 -0400 Received: from mga11.intel.com ([192.55.52.93]:64501 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242316AbhDSNe2 (ORCPT ); Mon, 19 Apr 2021 09:34:28 -0400 IronPort-SDR: 9TMB7mZEonMgeSRguQJkN4ixEpxJ6n5VJdiYqypKiXAzxwAz2qTZgd/bQnemdrgFyy4YzyCzUa PFwVFGkgMk5A== X-IronPort-AV: E=McAfee;i="6200,9189,9959"; a="192137388" X-IronPort-AV: E=Sophos;i="5.82,234,1613462400"; d="scan'208";a="192137388" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 06:33:55 -0700 IronPort-SDR: 0i+wEhGbCQP8Avpf0xm0vMRCRN4QY7mcaZHGnZjD6+zAPyurprhJLO6MMtOQfxvnKw4hGQi5iT gQehU6KPWmxA== X-IronPort-AV: E=Sophos;i="5.82,234,1613462400"; d="scan'208";a="426512252" Received: from blu2-mobl3.ccr.corp.intel.com (HELO [10.254.210.121]) ([10.254.210.121]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Apr 2021 06:33:51 -0700 Cc: baolu.lu@linux.intel.com, Alex Williamson , Cornelia Huck , Kirti Wankhede , wanghaibin.wang@huawei.com, jiangkunkun@huawei.com, yuzenghui@huawei.com, lushenming@huawei.com To: Keqian Zhu , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, Robin Murphy , Will Deacon , Joerg Roedel , Yi Sun , Jean-Philippe Brucker , Jonathan Cameron , Tian Kevin References: <20210413085457.25400-1-zhukeqian1@huawei.com> <20210413085457.25400-3-zhukeqian1@huawei.com> <491da550-dc54-42e6-ac91-13d411575fad@huawei.com> From: Lu Baolu Subject: Re: [PATCH v3 02/12] iommu: Add iommu_split_block interface Message-ID: Date: Mon, 19 Apr 2021 21:33:48 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <491da550-dc54-42e6-ac91-13d411575fad@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Keqian, On 2021/4/19 17:32, Keqian Zhu wrote: >>> +EXPORT_SYMBOL_GPL(iommu_split_block); >> Do you really have any consumers of this interface other than the dirty >> bit tracking? If not, I don't suggest to make this as a generic IOMMU >> interface. >> >> There is an implicit requirement for such interfaces. The >> iommu_map/unmap(iova, size) shouldn't be called at the same time. >> Currently there's no such sanity check in the iommu core. A poorly >> written driver could mess up the kernel by misusing this interface. > Yes, I don't think up a scenario except dirty tracking. > > Indeed, we'd better not make them as a generic interface. > > Do you have any suggestion that underlying iommu drivers can share these code but > not make it as a generic iommu interface? > > I have a not so good idea. Make the "split" interfaces as a static function, and > transfer the function pointer to start_dirty_log. But it looks weird and inflexible. I understand splitting/merging super pages is an optimization, but not a functional requirement. So is it possible to let the vendor iommu driver decide whether splitting super pages when starting dirty bit tracking and the opposite operation during when stopping it? The requirement for upper layer is that starting/stopping dirty bit tracking and mapping/unmapping are mutually exclusive. > > On the other hand, if a driver calls map/unmap with split/merge at the same time, > it's a bug of driver, it should follow the rule. > Best regards, baolu