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 7521BC43381 for ; Mon, 8 Mar 2021 07:05:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24F0A651F6 for ; Mon, 8 Mar 2021 07:05:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231418AbhCHHFB (ORCPT ); Mon, 8 Mar 2021 02:05:01 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:52733 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230446AbhCHHE3 (ORCPT ); Mon, 8 Mar 2021 02:04:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1615187068; 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=Nzo0gBDIUBxwZAv4o+4kKioscWKKFK2cbaFDxgnEqKA=; b=ZIbqBTLc6335gdUfGNCxFKFCeczrLEDEMdC+Osg2kea9iRsRw2CBZTcKXB/7Ah2PH1Sl3B Xvz9ExMC6JXLTAg2fdxrFJePcmYHeKIiX6X8O+eqnJWLioMcT3+v/CYpONe1rI8m1ItUUI a6fJ8eRas9dEZaQM5KTThMDpePXX6to= 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-310-SHYYpOAEPryJIiwRYOEROw-1; Mon, 08 Mar 2021 02:04:24 -0500 X-MC-Unique: SHYYpOAEPryJIiwRYOEROw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2A06980432E; Mon, 8 Mar 2021 07:04:22 +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 133C01971C; Mon, 8 Mar 2021 07:04:06 +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> <0b671aef-f2b2-6162-f407-7ca5178dbebb@redhat.com> From: Jason Wang Message-ID: <48d0a363-4f55-bf99-3653-315458643317@redhat.com> Date: Mon, 8 Mar 2021 15:04:05 +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 2.84 on 10.5.11.23 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2021/3/8 1:05 下午, Yongji Xie wrote: > On Mon, Mar 8, 2021 at 11:52 AM Jason Wang wrote: >> >> On 2021/3/8 11:45 上午, Yongji Xie wrote: >>> On Mon, Mar 8, 2021 at 11:17 AM Jason Wang wrote: >>>> 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(). >>>> >>> Yes. >>> >>>> 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? >>>> >>> In this case, I wonder what range can be obtained if userspace calls >>> VDUSE_IOTLB_GET_FD when the first I/O (e.g. 4K) occurs. [0, 4K] or [0, >>> 64M]? In current implementation, userspace will map [0, 64M]. >> >> It should still be [0, 64M). Do you see any issue? >> > Does it mean we still need to map the whole bounce buffer into itree > (dev->iommu) at initialization? It's your choice I think, the point is to use a single IOTLB for maintaining mappings of all types of pages (bounce, coherent, or shared). Thanks > > Thanks, > Yongji >