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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 014BBC4708D for ; Wed, 7 Dec 2022 18:34:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229918AbiLGSe1 (ORCPT ); Wed, 7 Dec 2022 13:34:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44614 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229908AbiLGSd4 (ORCPT ); Wed, 7 Dec 2022 13:33:56 -0500 Received: from verein.lst.de (verein.lst.de [213.95.11.211]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6DBDE22E; Wed, 7 Dec 2022 10:33:40 -0800 (PST) Received: by verein.lst.de (Postfix, from userid 2407) id D192568AFE; Wed, 7 Dec 2022 19:33:33 +0100 (CET) Date: Wed, 7 Dec 2022 19:33:33 +0100 From: Christoph Hellwig To: Jason Gunthorpe Cc: Christoph Hellwig , Lei Rao , kbusch@kernel.org, axboe@fb.com, kch@nvidia.com, sagi@grimberg.me, alex.williamson@redhat.com, cohuck@redhat.com, yishaih@nvidia.com, shameerali.kolothum.thodi@huawei.com, kevin.tian@intel.com, mjrosato@linux.ibm.com, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, kvm@vger.kernel.org, eddie.dong@intel.com, yadong.li@intel.com, yi.l.liu@intel.com, Konrad.wilk@oracle.com, stephen@eideticom.com, hang.yuan@intel.com Subject: Re: [RFC PATCH 1/5] nvme-pci: add function nvme_submit_vf_cmd to issue admin commands for VF driver. Message-ID: <20221207183333.GA7049@lst.de> References: <20221206153811.GB2266@lst.de> <20221206165503.GA8677@lst.de> <20221207075415.GB2283@lst.de> <20221207135203.GA22803@lst.de> <20221207163857.GB2010@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 07, 2022 at 01:31:44PM -0400, Jason Gunthorpe wrote: > > Sorry, I meant VF. Your continued using of SR-IOV teminology now keeps > > confusing my mind so much that I start mistyping things. > > Well, what words do you want to use? The same I've used through this whole thread: controlling and controlled function. > So I don't think I've learned anything more about your objection. > > "fundamentally broken" doesn't help The objection is that: - in hardware fundamentally only the controlling funtion can control live migration features on the controlled function, because the controlled function is assigned to a VM which has control over it. - for the same reason there is no portable way to even find the controlling function from a controlled function, unless you want to equate PF = controlling and VF = controlled, and even that breaks down in some corner cases - if you want to control live migration from the controlled VM you need a new vfio subdriver for a function that has absolutely no new functionality itself related to live migration (quirks for bugs excepted). So by this architecture you build a convoluted mess where you need tons of vfio subdrivers that mostly just talk to the driver for the controlling function, which they can't even sanely discover. That's what I keep calling fundamentally broken.