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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 E3C49C433B4 for ; Wed, 19 May 2021 15:23:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C66E0610CB for ; Wed, 19 May 2021 15:23:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346674AbhESPYy (ORCPT ); Wed, 19 May 2021 11:24:54 -0400 Received: from foss.arm.com ([217.140.110.172]:44984 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354730AbhESPYt (ORCPT ); Wed, 19 May 2021 11:24:49 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 34EF511D4; Wed, 19 May 2021 08:23:29 -0700 (PDT) Received: from [10.57.66.179] (unknown [10.57.66.179]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7E1C63F73D; Wed, 19 May 2021 08:23:27 -0700 (PDT) Subject: Re: [PATCH 3/6] vfio: remove the unused mdev iommu hook To: Joerg Roedel , Jason Gunthorpe Cc: "Tian, Kevin" , "kvm@vger.kernel.org" , Will Deacon , Kirti Wankhede , "iommu@lists.linux-foundation.org" , Alex Williamson , David Woodhouse , Christoph Hellwig , "linux-arm-kernel@lists.infradead.org" References: <20210513120058.GG1096940@ziepe.ca> <20210514121925.GI1096940@ziepe.ca> <20210514133143.GK1096940@ziepe.ca> <20210517123010.GO1096940@ziepe.ca> <20210517133500.GP1096940@ziepe.ca> From: Robin Murphy Message-ID: <131327e3-5066-7a88-5b3c-07013585eb01@arm.com> Date: Wed, 19 May 2021 16:23:21 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 2021-05-17 16:35, Joerg Roedel wrote: > On Mon, May 17, 2021 at 10:35:00AM -0300, Jason Gunthorpe wrote: >> Well, I'm sorry, but there is a huge other thread talking about the >> IOASID design in great detail and why this is all needed. Jumping into >> this thread without context and basically rejecting all the >> conclusions that were reached over the last several weeks is really >> not helpful - especially since your objection is not technical. >> >> I think you should wait for Intel to put together the /dev/ioasid uAPI >> proposal and the example use cases it should address then you can give >> feedback there, with proper context. > > Yes, I think the next step is that someone who read the whole thread > writes up the conclusions and a rough /dev/ioasid API proposal, also > mentioning the use-cases it addresses. Based on that we can discuss the > implications this needs to have for IOMMU-API and code. > > From the use-cases I know the mdev concept is just fine. But if there is > a more generic one we can talk about it. Just to add another voice here, I have some colleagues working on drivers where they want to use SMMU Substream IDs for a single hardware block to operate on multiple iommu_domains managed entirely within the kernel. Using an mdev-like approach with aux domains is pretty much the ideal fit for this use-case, while all the IOASID discussion appears centred on SVA and userspace interfaces, and as such barely relevant if at all. I seem to recall a non-trivial amount of effort going into the aux domain design too, so the promise of replacing it with "a big TBD" just because vfio-mdev turned out to be awful hardly fills me with enthusiasm either :/ Robin.