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=-8.4 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 1B4F2C433E0 for ; Wed, 30 Dec 2020 06:11:21 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 917702085B for ; Wed, 30 Dec 2020 06:11:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 917702085B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 70DD58D0061; Wed, 30 Dec 2020 01:11:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6BD418D0081; Wed, 30 Dec 2020 01:11:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 50F2D8D0061; Wed, 30 Dec 2020 01:11:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0109.hostedemail.com [216.40.44.109]) by kanga.kvack.org (Postfix) with ESMTP id 35D588D007F for ; Wed, 30 Dec 2020 01:11:19 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id E86C1181AEF09 for ; Wed, 30 Dec 2020 06:11:18 +0000 (UTC) X-FDA: 77648926236.07.end01_09090c0274a2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin07.hostedemail.com (Postfix) with ESMTP id D0E321803F9A7 for ; Wed, 30 Dec 2020 06:11:18 +0000 (UTC) X-HE-Tag: end01_09090c0274a2 X-Filterd-Recvd-Size: 5340 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf09.hostedemail.com (Postfix) with ESMTP for ; Wed, 30 Dec 2020 06:11:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1609308677; 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=HR5VQjVbyjmspTne1yUEQIA+lboTKLXwct9mHhTRH6o=; b=dofCJCujd7Tkp3pmlZnZGWI15VNpitsHFXfk8+SCXpgshvv5cSxCAwi28tUmXTgHsnx6fa uhFnfUwT8U83a63gBQjRHbU19KMp3LKlSeguHdPk8ZSrQIIFWQl5Nhg6Pd07l/MoMcFEq1 p+X6gY0F5J98z3iE0VJC6gXWJxjFVFc= 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-279-7O4wQ_a9MSKDf-vq6j4Bxw-1; Wed, 30 Dec 2020 01:11:13 -0500 X-MC-Unique: 7O4wQ_a9MSKDf-vq6j4Bxw-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F07BFE760; Wed, 30 Dec 2020 06:11:10 +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 D2DA31007617; Wed, 30 Dec 2020 06:10:58 +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: Date: Wed, 30 Dec 2020 14:10:57 +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-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2020/12/29 =E4=B8=8B=E5=8D=886:26, 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 wrot= e: >>>> >>>> On 2020/12/28 =E4=B8=8B=E5=8D=884:14, Yongji Xie wrote: >>>>>> I see. So all the above two questions are because VHOST_IOTLB_INVA= LIDATE >>>>>> 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 relayi= ng >>>>>> 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 repl= ied >>>>> by userspace. Could it solve this problem? >>>> >>>> I was thinking whether or not we need to generate IOTLB_INVALIDAT= E >>>> 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? > 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=20 IOTLB_UMAP message. Thanks > > Thanks, > Yongji >