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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 7689EC433DB for ; Mon, 8 Mar 2021 03:18:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 419E56514C for ; Mon, 8 Mar 2021 03:18:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233783AbhCHDSM (ORCPT ); Sun, 7 Mar 2021 22:18:12 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:58129 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232583AbhCHDRb (ORCPT ); Sun, 7 Mar 2021 22:17:31 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615173450; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=lncFpbesf3+Cf0X7NC13aXAoRjJq1HSTiKB3om5hTS8=; b=Xt81nN/sfq0ceLpPB6nZcNLvKPJf12djR7VbPt/Bjm8q+yXatEg3bsjTSIPgNRyD9D6RgZ 9uGBBK4sikHNhNXO6hT9673gDUKj+Rs8gS6L08oPVMUMfRpHZTwkML+4BqiND5Mi6aaEMM 23HrFsMyRaU0d3gmTi27B+m1n+yDK8E= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-437-LK-aPUdXMEO8cZ6cb1sLtg-1; Sun, 07 Mar 2021 22:17:26 -0500 X-MC-Unique: LK-aPUdXMEO8cZ6cb1sLtg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5B80857; Mon, 8 Mar 2021 03:17:24 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-193.pek2.redhat.com [10.72.13.193]) by smtp.corp.redhat.com (Postfix) with ESMTP id 719CA5C5FC; Mon, 8 Mar 2021 03:17:10 +0000 (UTC) Subject: Re: [RFC v4 06/11] vduse: Implement an MMU-based IOMMU driver To: Yongji Xie Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , Stefano Garzarella , Parav Pandit , Bob Liu , Christoph Hellwig , Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, Jens Axboe , bcrl@kvack.org, Jonathan Corbet , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org References: <20210223115048.435-1-xieyongji@bytedance.com> <20210223115048.435-7-xieyongji@bytedance.com> <573ab913-55ce-045a-478f-1200bd78cf7b@redhat.com> <4db35f8c-ee3a-90fb-8d14-5d6014b4f6fa@redhat.com> <2652f696-faf7-26eb-a8b2-c4cfe3aaed15@redhat.com> From: Jason Wang Message-ID: Date: Mon, 8 Mar 2021 11:17:08 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.16; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-GB X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2021/3/5 3:59 下午, Yongji Xie wrote: > On Fri, Mar 5, 2021 at 3:27 PM Jason Wang wrote: >> >> On 2021/3/5 3:13 下午, Yongji Xie wrote: >>> On Fri, Mar 5, 2021 at 2:52 PM Jason Wang wrote: >>>> On 2021/3/5 2:15 下午, Yongji Xie wrote: >>>> >>>> Sorry if I've asked this before. >>>> >>>> But what's the reason for maintaing a dedicated IOTLB here? I think we >>>> could reuse vduse_dev->iommu since the device can not be used by both >>>> virtio and vhost in the same time or use vduse_iova_domain->iotlb for >>>> set_map(). >>>> >>>> The main difference between domain->iotlb and dev->iotlb is the way to >>>> deal with bounce buffer. In the domain->iotlb case, bounce buffer >>>> needs to be mapped each DMA transfer because we need to get the bounce >>>> pages by an IOVA during DMA unmapping. In the dev->iotlb case, bounce >>>> buffer only needs to be mapped once during initialization, which will >>>> be used to tell userspace how to do mmap(). >>>> >>>> Also, since vhost IOTLB support per mapping token (opauqe), can we use >>>> that instead of the bounce_pages *? >>>> >>>> Sorry, I didn't get you here. Which value do you mean to store in the >>>> opaque pointer？ >>>> >>>> So I would like to have a way to use a single IOTLB for manage all kinds >>>> of mappings. Two possible ideas: >>>> >>>> 1) map bounce page one by one in vduse_dev_map_page(), in >>>> VDUSE_IOTLB_GET_FD, try to merge the result if we had the same fd. Then >>>> for bounce pages, userspace still only need to map it once and we can >>>> maintain the actual mapping by storing the page or pa in the opaque >>>> field of IOTLB entry. >>>> >>>> Looks like userspace still needs to unmap the old region and map a new >>>> region (size is changed) with the fd in each VDUSE_IOTLB_GET_FD ioctl. >>>> >>>> >>>> I don't get here. Can you give an example? >>>> >>> For example, userspace needs to process two I/O requests (one page per >>> request). To process the first request, userspace uses >>> VDUSE_IOTLB_GET_FD ioctl to query the iova region (0 ~ 4096) and mmap >>> it. >> >> I think in this case we should let VDUSE_IOTLB_GET_FD return the maximum >> range as far as they are backed by the same fd. >> > But now the bounce page is mapped one by one. The second page (4096 ~ > 8192) might not be mapped when userspace is processing the first > request. So the maximum range is 0 ~ 4096 at that time. > > Thanks, > Yongji A question, if I read the code correctly, VDUSE_IOTLB_GET_FD will return the whole bounce map range which is setup in vduse_dev_map_page()? So my understanding is that usersapce may choose to map all its range via mmap(). So if we 'map' bounce page one by one in vduse_dev_map_page(). (Here 'map' means using multiple itree entries instead of a single one). Then in the VDUSE_IOTLB_GET_FD we can keep traversing itree (dev->iommu) until the range is backed by a different file. With this, there's no userspace visible changes and there's no need for the domain->iotlb? Thanks >