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 54B89C3A5A6 for ; Thu, 19 Sep 2019 13:08:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 344AF21924 for ; Thu, 19 Sep 2019 13:08:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388686AbfISNIf (ORCPT ); Thu, 19 Sep 2019 09:08:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39868 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732271AbfISNIf (ORCPT ); Thu, 19 Sep 2019 09:08:35 -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 2765189810C; Thu, 19 Sep 2019 13:08:35 +0000 (UTC) Received: from [10.72.12.81] (ovpn-12-81.pek2.redhat.com [10.72.12.81]) by smtp.corp.redhat.com (Postfix) with ESMTP id ABF825D9CC; Thu, 19 Sep 2019 13:08:22 +0000 (UTC) Subject: Re: [RFC v4 0/3] vhost: introduce mdev based hardware backend To: "Michael S. Tsirkin" Cc: Tiwei Bie , 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> From: Jason Wang Message-ID: Date: Thu, 19 Sep 2019 21:08:11 +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: <20190918102923-mutt-send-email-mst@kernel.org> 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-4.6.2 (mx1.redhat.com [10.5.110.67]); Thu, 19 Sep 2019 13:08:35 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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. Thanks >> Yes, it is. >> >> Thanks >> >>