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 D2277C433B4 for ; Tue, 20 Apr 2021 07:32:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9551F61155 for ; Tue, 20 Apr 2021 07:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229722AbhDTHdL (ORCPT ); Tue, 20 Apr 2021 03:33:11 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:16142 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229669AbhDTHdJ (ORCPT ); Tue, 20 Apr 2021 03:33:09 -0400 Received: from DGGEMS412-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4FPb0y06cXzpZP2; Tue, 20 Apr 2021 15:29:38 +0800 (CST) Received: from [10.174.187.224] (10.174.187.224) by DGGEMS412-HUB.china.huawei.com (10.3.19.212) with Microsoft SMTP Server id 14.3.498.0; Tue, 20 Apr 2021 15:32:26 +0800 Subject: Re: [PATCH v3 02/12] iommu: Add iommu_split_block interface To: Lu Baolu , , , , 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> <3c34baf1-6a57-5666-38a2-0c9d6188b8b8@linux.intel.com> CC: Alex Williamson , Cornelia Huck , Kirti Wankhede , , , , From: Keqian Zhu Message-ID: Date: Tue, 20 Apr 2021 15:32:25 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <3c34baf1-6a57-5666-38a2-0c9d6188b8b8@linux.intel.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.187.224] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Baolu, Cheers for the your quick reply. On 2021/4/20 10:09, Lu Baolu wrote: > Hi Keqian, > > On 4/20/21 9:25 AM, Keqian Zhu wrote: >> Hi Baolu, >> >> On 2021/4/19 21:33, Lu Baolu wrote: >>> 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 >> Right. If I understand you correct, actually that is what this series does. > > I mean to say no generic APIs, jut do it by the iommu subsystem itself. > It's totally transparent to the upper level, just like what map() does. > The upper layer doesn't care about either super page or small page is > in use when do a mapping, right? > > If you want to consolidate some code, how about putting them in > start/stop_tracking()? Yep, this reminds me. What we want to reuse is the logic of "chunk by chunk" in split(). We can implement switch_dirty_log to be "chunk by chunk" too (just the same as sync/clear), then the vendor iommu driver can invoke it's own private implementation of split(). So we can completely remove split() in the IOMMU core layer. example code logic iommu.c: switch_dirty_log(big range) { for_each_iommu_page(big range) { ops->switch_dirty_log(iommu_pgsize) } } vendor iommu driver: switch_dirty_log(iommu_pgsize) { if (enable) { ops->split_block(iommu_pgsize) /* And other actions, such as enable hardware capability */ } else { for_each_continuous_physical_address(iommu_pgsize) ops->merge_page() } } Besides, vendor iommu driver can invoke split() in clear_dirty_log instead of in switch_dirty_log. The benefit is that we usually clear dirty log gradually during dirty tracking, then we can split large page mapping gradually, which speedup start_dirty_log and make less side effect on DMA performance. Does it looks good for you? Thanks, Keqian