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 0884CC3A5A6 for ; Fri, 20 Sep 2019 02:37:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D46A4217D6 for ; Fri, 20 Sep 2019 02:37:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391325AbfITChO (ORCPT ); Thu, 19 Sep 2019 22:37:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51248 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389457AbfITChO (ORCPT ); Thu, 19 Sep 2019 22:37:14 -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 9A1B93082E44; Fri, 20 Sep 2019 02:37:13 +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 717C95D9CD; Fri, 20 Sep 2019 02:37:00 +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@___> <43aaf7dc-f08b-8898-3c55-908ff4d68866@redhat.com> <20190920021630.GA4108@___> From: Jason Wang Message-ID: <09dced89-3892-be43-3748-054ce21e37ab@redhat.com> Date: Fri, 20 Sep 2019 10:36:57 +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: <20190920021630.GA4108@___> 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 [10.5.110.46]); Fri, 20 Sep 2019 02:37:13 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/9/20 上午10:16, Tiwei Bie wrote: > On Fri, Sep 20, 2019 at 09:30:58AM +0800, Jason Wang wrote: >> 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 ... >> >> To clarify, this should be done through the id_table fields in >> vhost_mdev_driver, and it should claim it supports virtio-mdev device only: >> >> >> static struct mdev_class_id id_table[] = { >>     { MDEV_ID_VIRTIO }, >>     { 0 }, >> }; >> >> >> static struct mdev_driver vhost_mdev_driver = { >>     ... >>     .id_table = id_table, >> } > In this way, both of virtio-mdev and vhost-mdev will try to > take this device. We may want a way to let vhost-mdev take this > device only when users explicitly ask it to do it. Or maybe we > can have a different MDEV_ID for vhost-mdev but share the device > ops with virtio-mdev. I think it's similar to virtio-pci vs vfio-pci. User can choose to switch the driver through bind/unbind. > >> >>> return vfio_add_group_dev(dev, &vfio_vhost_mdev_dev_ops, mdev); >> >> And in vfio_vhost_mdev_ops, all its need is to just implement vhost-net >> ioctl and translate them to virtio-mdev transport (e.g device_ops I proposed >> or ioctls other whatever other method) API. > I see, so my previous understanding is basically correct: > > https://lkml.org/lkml/2019/9/17/332 > > I.e. we won't have a separate vhost fd and we will do all vhost > ioctls on the VFIO device fd backed by this new VFIO driver. Yes. Thanks > >> And it could have a dummy ops >> implementation for the other device_ops. >> >> >>> } >>> >>> 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. >> >> Then what vhost-mdev char device did is just forwarding ioctl back to this >> vfio device fd which seems a overkill. It's simpler that just do ioctl on >> the device ops directly. > Yes. > > Thanks, > Tiwei > > >> Thanks >> >> >>> Thanks, >>> Tiwei >>> >>>> Thanks >>>> >>>> >>>>>> Yes, it is. >>>>>> >>>>>> Thanks >>>>>> >>>>>>