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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 1CD1FC4CEC9 for ; Tue, 17 Sep 2019 03:32:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0FD820650 for ; Tue, 17 Sep 2019 03:32:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392232AbfIQDcS (ORCPT ); Mon, 16 Sep 2019 23:32:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58840 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730000AbfIQDcR (ORCPT ); Mon, 16 Sep 2019 23:32:17 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6592F10CC1E4; Tue, 17 Sep 2019 03:32:17 +0000 (UTC) Received: from [10.72.12.121] (ovpn-12-121.pek2.redhat.com [10.72.12.121]) by smtp.corp.redhat.com (Postfix) with ESMTP id DB54460126; Tue, 17 Sep 2019 03:32:05 +0000 (UTC) Subject: Re: [RFC v4 0/3] vhost: introduce mdev based hardware backend To: Tiwei Bie , mst@redhat.com, alex.williamson@redhat.com, maxime.coquelin@redhat.com Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, dan.daly@intel.com, cunming.liang@intel.com, zhihong.wang@intel.com, lingshan.zhu@intel.com References: <20190917010204.30376-1-tiwei.bie@intel.com> From: Jason Wang Message-ID: <993841ed-942e-c90b-8016-8e7dc76bf13a@redhat.com> Date: Tue, 17 Sep 2019 11:32:03 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190917010204.30376-1-tiwei.bie@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Tue, 17 Sep 2019 03:32:17 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/9/17 上午9:02, Tiwei Bie wrote: > This RFC is to demonstrate below ideas, > > a) Build vhost-mdev on top of the same abstraction defined in > the virtio-mdev series [1]; > > b) Introduce /dev/vhost-mdev to do vhost ioctls and support > setting mdev device as backend; > > Now the userspace API looks like this: > > - Userspace generates a compatible mdev device; > > - Userspace opens this mdev device with VFIO API (including > doing IOMMU programming for this mdev device with VFIO's > container/group based interface); > > - Userspace opens /dev/vhost-mdev and gets vhost fd; > > - Userspace uses vhost ioctls to setup vhost (userspace should > do VHOST_MDEV_SET_BACKEND ioctl with VFIO group fd and device > fd first before doing other vhost ioctls); > > Only compile test has been done for this series for now. Have a hard thought on the architecture: 1) Create a vhost char device and pass vfio mdev device fd to it as a backend and translate vhost-mdev ioctl to virtio mdev transport (e.g read/write). DMA was done through the VFIO DMA mapping on the container that is attached. We have two more choices: 2) Use vfio-mdev but do not create vhost-mdev device, instead, just implement vhost ioctl on vfio_device_ops, and translate them into virtio-mdev transport or just pass ioctl to parent. 3) Don't use vfio-mdev, create a new vhost-mdev driver, during probe still try to add dev to vfio group and talk to parent with device specific ops So I have some questions: 1) Compared to method 2, what's the advantage of creating a new vhost char device? I guess it's for keep the API compatibility? 2) For method 2, is there any easy way for user/admin to distinguish e.g ordinary vfio-mdev for vhost from ordinary vfio-mdev?  I saw you introduce ops matching helper but it's not friendly to management. 3) A drawback of 1) and 2) is that it must follow vfio_device_ops that assumes the parameter comes from userspace, it prevents support kernel virtio drivers. 4) So comes the idea of method 3, since it register a new vhost-mdev driver, we can use device specific ops instead of VFIO ones, then we can have a common API between vDPA parent and vhost-mdev/virtio-mdev drivers. What's your thoughts? Thanks > > RFCv3: https://patchwork.kernel.org/patch/11117785/ > > [1] https://lkml.org/lkml/2019/9/10/135 > > Tiwei Bie (3): > vfio: support getting vfio device from device fd > vfio: support checking vfio driver by device ops > vhost: introduce mdev based hardware backend > > drivers/vfio/mdev/vfio_mdev.c | 3 +- > drivers/vfio/vfio.c | 32 +++ > drivers/vhost/Kconfig | 9 + > drivers/vhost/Makefile | 3 + > drivers/vhost/mdev.c | 462 +++++++++++++++++++++++++++++++ > drivers/vhost/vhost.c | 39 ++- > drivers/vhost/vhost.h | 6 + > include/linux/vfio.h | 11 + > include/uapi/linux/vhost.h | 10 + > include/uapi/linux/vhost_types.h | 5 + > 10 files changed, 573 insertions(+), 7 deletions(-) > create mode 100644 drivers/vhost/mdev.c >