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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 D0408C3A5A6 for ; Fri, 20 Sep 2019 00:59:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AD985206C2 for ; Fri, 20 Sep 2019 00:59:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394538AbfITA7q (ORCPT ); Thu, 19 Sep 2019 20:59:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43612 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389293AbfITA7q (ORCPT ); Thu, 19 Sep 2019 20:59:46 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 2C55B81DE7; Fri, 20 Sep 2019 00:59:46 +0000 (UTC) Received: from [10.72.12.88] (ovpn-12-88.pek2.redhat.com [10.72.12.88]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4F6D75D9CD; Fri, 20 Sep 2019 00:59:34 +0000 (UTC) Subject: Re: [RFC v4 0/3] vhost: introduce mdev based hardware backend To: Tiwei Bie Cc: "Michael S. Tsirkin" , alex.williamson@redhat.com, maxime.coquelin@redhat.com, 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> <993841ed-942e-c90b-8016-8e7dc76bf13a@redhat.com> <20190917105801.GA24855@___> <20190918102923-mutt-send-email-mst@kernel.org> <20190919154552.GA27657@___> From: Jason Wang Message-ID: <11bc30a9-1cf5-4a5f-109a-f307d70c35fa@redhat.com> Date: Fri, 20 Sep 2019 08:59:32 +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: <20190919154552.GA27657@___> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Fri, 20 Sep 2019 00:59:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/9/19 下午11:45, Tiwei Bie wrote: > On Thu, Sep 19, 2019 at 09:08:11PM +0800, Jason Wang wrote: >> On 2019/9/18 下午10:32, Michael S. Tsirkin wrote: >>>>>> 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? >>>>> One benefit is that we can avoid doing vhost ioctls on >>>>> VFIO device fd. >>>> Yes, but any benefit from doing this? >>> It does seem a bit more modular, but it's certainly not a big deal. >> Ok, if we go this way, it could be as simple as provide some callback to >> vhost, then vhost can just forward the ioctl through parent_ops. >> >>>>>> 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 think device-api could be a choice. >>>> Ok. >>>> >>>> >>>>>> I saw you introduce >>>>>> ops matching helper but it's not friendly to management. >>>>> The ops matching helper is just to check whether a given >>>>> vfio-device is based on a mdev device. >>>>> >>>>>> 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. >>>>> As the above draft shows, this requires introducing a new >>>>> VFIO device driver. I think Alex's opinion matters here. >> Just to clarify, a new type of mdev driver but provides dummy >> vfio_device_ops for VFIO to make container DMA ioctl work. > I see. Thanks! IIUC, you mean we can provide a very tiny > VFIO device driver in drivers/vhost/mdev.c, e.g.: > > static int vfio_vhost_mdev_open(void *device_data) > { > if (!try_module_get(THIS_MODULE)) > return -ENODEV; > return 0; > } > > static void vfio_vhost_mdev_release(void *device_data) > { > module_put(THIS_MODULE); > } > > static const struct vfio_device_ops vfio_vhost_mdev_dev_ops = { > .name = "vfio-vhost-mdev", > .open = vfio_vhost_mdev_open, > .release = vfio_vhost_mdev_release, > }; > > static int vhost_mdev_probe(struct device *dev) > { > struct mdev_device *mdev = to_mdev_device(dev); > > ... Check the mdev device_id proposed in ... > ... https://lkml.org/lkml/2019/9/12/151 ... > > return vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, mdev); > } > > static void vhost_mdev_remove(struct device *dev) > { > vfio_del_group_dev(dev); > } > > static struct mdev_driver vhost_mdev_driver = { > .name = "vhost_mdev", > .probe = vhost_mdev_probe, > .remove = vhost_mdev_remove, > }; > > So we can bind above mdev driver to the virtio-mdev compatible > mdev devices when we want to use vhost-mdev. > > After binding above driver to the mdev device, we can setup IOMMU > via VFIO and get VFIO device fd of this mdev device, and pass it > to vhost fd (/dev/vhost-mdev) with a SET_BACKEND ioctl. > > Thanks, > Tiwei Yes, something like this. Thanks >> Thanks >> >> >>>> Yes, it is. >>>> >>>> Thanks >>>> >>>>