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=-10.7 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=unavailable 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 D929AC4332B for ; Wed, 30 Dec 2020 08:43:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A9CAE21D1B for ; Wed, 30 Dec 2020 08:43:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726277AbgL3InT (ORCPT ); Wed, 30 Dec 2020 03:43:19 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:24242 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725814AbgL3InS (ORCPT ); Wed, 30 Dec 2020 03:43:18 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1609317711; 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=Nxql4zOLePCw/DPHwTjONsd++E57uymBDbcJD4zzipA=; b=VXQJTb1xO7KcAPCh9G0167TantCPrtbVRn75eFg551nkjueQ2k0S27W4G7YdlyztyJoBKn ZJhoBk2Oc+dgPHZaj7UIuJZYGHFlwrLXoeFOZ8ueGb00TGw66T1Ho8ULRlZIT6PJDDX07m 1A2xzfGhZ8l+H7CNjYE/3Z4iYn2Um6s= 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-433-zpv0_H9vOcyfBsFlNAK1zg-1; Wed, 30 Dec 2020 03:41:47 -0500 X-MC-Unique: zpv0_H9vOcyfBsFlNAK1zg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2C8FB180A08A; Wed, 30 Dec 2020 08:41:45 +0000 (UTC) Received: from [10.72.13.30] (ovpn-13-30.pek2.redhat.com [10.72.13.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7751E5D6AB; Wed, 30 Dec 2020 08:41:32 +0000 (UTC) Subject: Re: [RFC v2 09/13] vduse: Add support for processing vhost iotlb message To: Yongji Xie Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , sgarzare@redhat.com, Parav Pandit , akpm@linux-foundation.org, Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, axboe@kernel.dk, bcrl@kvack.org, corbet@lwn.net, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org References: <20201222145221.711-1-xieyongji@bytedance.com> <0e6faf9c-117a-e23c-8d6d-488d0ec37412@redhat.com> <2b24398c-e6d9-14ec-2c0d-c303d528e377@redhat.com> <1356137727.40748805.1609233068675.JavaMail.zimbra@redhat.com> From: Jason Wang Message-ID: <3fc6a132-9fc2-c4e2-7fb1-b5a8bfb771fa@redhat.com> Date: Wed, 30 Dec 2020 16:41:30 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2020/12/30 下午3:09, Yongji Xie wrote: > On Wed, Dec 30, 2020 at 2:11 PM Jason Wang wrote: >> >> On 2020/12/29 下午6:26, Yongji Xie wrote: >>> On Tue, Dec 29, 2020 at 5:11 PM Jason Wang wrote: >>>> >>>> ----- Original Message ----- >>>>> On Mon, Dec 28, 2020 at 4:43 PM Jason Wang wrote: >>>>>> On 2020/12/28 下午4:14, Yongji Xie wrote: >>>>>>>> I see. So all the above two questions are because VHOST_IOTLB_INVALIDATE >>>>>>>> is expected to be synchronous. This need to be solved by tweaking the >>>>>>>> current VDUSE API or we can re-visit to go with descriptors relaying >>>>>>>> first. >>>>>>>> >>>>>>> Actually all vdpa related operations are synchronous in current >>>>>>> implementation. The ops.set_map/dma_map/dma_unmap should not return >>>>>>> until the VDUSE_UPDATE_IOTLB/VDUSE_INVALIDATE_IOTLB message is replied >>>>>>> by userspace. Could it solve this problem? >>>>>> I was thinking whether or not we need to generate IOTLB_INVALIDATE >>>>>> message to VDUSE during dma_unmap (vduse_dev_unmap_page). >>>>>> >>>>>> If we don't, we're probably fine. >>>>>> >>>>> It seems not feasible. This message will be also used in the >>>>> virtio-vdpa case to notify userspace to unmap some pages during >>>>> consistent dma unmapping. Maybe we can document it to make sure the >>>>> users can handle the message correctly. >>>> Just to make sure I understand your point. >>>> >>>> Do you mean you plan to notify the unmap of 1) streaming DMA or 2) >>>> coherent DMA? >>>> >>>> For 1) you probably need a workqueue to do that since dma unmap can >>>> be done in irq or bh context. And if usrspace does't do the unmap, it >>>> can still access the bounce buffer (if you don't zap pte)? >>>> >>> I plan to do it in the coherent DMA case. >> >> Any reason for treating coherent DMA differently? >> > Now the memory of the bounce buffer is allocated page by page in the > page fault handler. So it can't be used in coherent DMA mapping case > which needs some memory with contiguous virtual addresses. I can use > vmalloc() to do allocation for the bounce buffer instead. But it might > cause some memory waste. Any suggestion? I may miss something. But I don't see a relationship between the IOTLB_UNMAP and vmalloc(). > >>> It's true that userspace can >>> access the dma buffer if userspace doesn't do the unmap. But the dma >>> pages would not be freed and reused unless user space called munmap() >>> for them. >> >> I wonder whether or not we could recycle IOVA in this case to avoid the >> IOTLB_UMAP message. >> > We can achieve that if we use vmalloc() to do allocation for the > bounce buffer which can be used in coherent DMA mapping case. But > looks like we still have no way to avoid the IOTLB_UMAP message in > vhost-vdpa case. I think that's fine. For virtio-vdpa, from VDUSE userspace perspective, it works like a driver that is using SWIOTLB in this case. Thanks > > Thanks, > Yongji >