From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-pci-owner@kernel.org>
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 B6EDCC433EF
	for <linux-pci@archiver.kernel.org>; Wed, 23 Feb 2022 18:20:48 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S241030AbiBWSVO (ORCPT <rfc822;linux-pci@archiver.kernel.org>);
        Wed, 23 Feb 2022 13:21:14 -0500
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51752 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S243811AbiBWSVN (ORCPT
        <rfc822;linux-pci@vger.kernel.org>); Wed, 23 Feb 2022 13:21:13 -0500
Received: from foss.arm.com (foss.arm.com [217.140.110.172])
        by lindbergh.monkeyblade.net (Postfix) with ESMTP id 0AA804A3DF;
        Wed, 23 Feb 2022 10:20:45 -0800 (PST)
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 B22C8D6E;
        Wed, 23 Feb 2022 10:20:44 -0800 (PST)
Received: from [10.57.40.147] (unknown [10.57.40.147])
        by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 23D623F70D;
        Wed, 23 Feb 2022 10:20:41 -0800 (PST)
Message-ID: <2114e6e6-68cc-4552-8781-0a824de2c0de@arm.com>
Date:   Wed, 23 Feb 2022 18:20:36 +0000
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:91.0) Gecko/20100101
 Thunderbird/91.6.1
Subject: Re: [PATCH v6 01/11] iommu: Add dma ownership management interfaces
Content-Language: en-GB
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Stuart Yoder <stuyoder@gmail.com>, rafael@kernel.org,
        David Airlie <airlied@linux.ie>, linux-pci@vger.kernel.org,
        Thierry Reding <thierry.reding@gmail.com>,
        Diana Craciun <diana.craciun@oss.nxp.com>,
        Dmitry Osipenko <digetx@gmail.com>,
        Will Deacon <will@kernel.org>, Ashok Raj <ashok.raj@intel.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        Christoph Hellwig <hch@infradead.org>,
        Kevin Tian <kevin.tian@intel.com>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        kvm@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Cornelia Huck <cohuck@redhat.com>,
        linux-kernel@vger.kernel.org, Li Yang <leoyang.li@nxp.com>,
        iommu@lists.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@intel.com>,
        Daniel Vetter <daniel@ffwll.ch>
References: <20220218005521.172832-1-baolu.lu@linux.intel.com>
 <20220218005521.172832-2-baolu.lu@linux.intel.com>
 <f830c268-daca-8e8f-a429-0c80496a7273@arm.com>
 <20220223180244.GA390403@nvidia.com>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <20220223180244.GA390403@nvidia.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk
List-ID: <linux-pci.vger.kernel.org>
X-Mailing-List: linux-pci@vger.kernel.org

On 2022-02-23 18:02, Jason Gunthorpe via iommu wrote:
> On Wed, Feb 23, 2022 at 06:00:06PM +0000, Robin Murphy wrote:
> 
>> ...and equivalently just set owner_cnt directly to 0 here. I don't see a
>> realistic use-case for any driver to claim the same group more than once,
>> and allowing it in the API just feels like opening up various potential
>> corners for things to get out of sync.
> 
> I am Ok if we toss it out to get this merged, as there is no in-kernel
> user right now.
> 
> Something will have to come back for iommufd, but we can look at what
> is best suited then.

If iommufd plans to be too dumb to keep track of whether it already owns 
a given group or not, I can't see it dealing with attaching that group 
to a single domain no more than once, either ;)

Robin.