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Fri, 19 Nov 2021 05:44:35 +0000 From: "Tian, Kevin" To: Jason Gunthorpe CC: Lu Baolu , Christoph Hellwig , Greg Kroah-Hartman , "Joerg Roedel" , Alex Williamson , Bjorn Helgaas , "Raj, Ashok" , Chaitanya Kulkarni , "kvm@vger.kernel.org" , "rafael@kernel.org" , "linux-pci@vger.kernel.org" , Cornelia Huck , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "Pan, Jacob jun" , Diana Craciun , "Will Deacon" Subject: RE: [PATCH 01/11] iommu: Add device dma ownership set/release interfaces Thread-Topic: [PATCH 01/11] iommu: Add device dma ownership set/release interfaces Thread-Index: AQHX2cX72SW3lNH8302ZqE4v8PTHlawEkdAAgADVRACAAMX3gIACZvYQgAC6LICAAQu4sA== Date: Fri, 19 Nov 2021 05:44:35 +0000 Message-ID: References: <20211115020552.2378167-1-baolu.lu@linux.intel.com> <20211115020552.2378167-2-baolu.lu@linux.intel.com> <20211116134603.GA2105516@nvidia.com> <20211118133325.GO2105516@nvidia.com> In-Reply-To: <20211118133325.GO2105516@nvidia.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-version: 11.6.200.16 dlp-product: dlpe-windows dlp-reaction: no-action authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BN9PR11MB5433.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 138a110b-8d55-494e-daf1-08d9ab1fab0a X-MS-Exchange-CrossTenant-originalarrivaltime: 19 Nov 2021 05:44:35.0920 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: U0IZm3EJ6GW/suwo3q626mdBHLM/ErBD+6Z3Mmn2Zz+CrRMluN1toK+jIcZKwgdHvgKzVh/WSYCA2QW9RLLlJQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR11MB5338 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Jason Gunthorpe > Sent: Thursday, November 18, 2021 9:33 PM >=20 > > In concept a singleton group is different from a > > multi-devices group which has only one device bound to driver... >=20 > Really? Why? I don't see it that way.. >=20 > A singleton group is just a multi-device group that hasn't been > hotplugged yet. >=20 > We don't seem to have the concept of a "true" singleton group which is > permanently single due to HW features. >=20 > > This series aims to avoid conflict having both user and kernel drivers > > mixed in a multi-devices group. Well, the difference is just in literal. I don't know the background why the existing iommu_attach_device() users want to do it this way. But given the condition in iommu_attach_device() it could in theory imply some unknown hardware-level side effect which=20 may break the desired functionality once the group size grows=20 beyond singleton. Is it a real case? I don't know... You are now redefining that condition from singleton group to multi-devices group with single driver bound. As long as no object from existing driver users, I'm fine with it. But still want to raise awareness as it does change the existing semantics (though might be considered as an imperfect way). Thanks Kevin 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24E22C433F5 for ; Fri, 19 Nov 2021 05:44:43 +0000 (UTC) Received: from smtp1.osuosl.org (smtp1.osuosl.org [140.211.166.138]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C316E61AF0 for ; Fri, 19 Nov 2021 05:44:42 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org C316E61AF0 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp1.osuosl.org (Postfix) with ESMTP id 7C88A81A33; Fri, 19 Nov 2021 05:44:42 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp1.osuosl.org ([127.0.0.1]) by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id c6ShlSt3H9EY; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > From: Jason Gunthorpe > Sent: Thursday, November 18, 2021 9:33 PM > > > In concept a singleton group is different from a > > multi-devices group which has only one device bound to driver... > > Really? Why? I don't see it that way.. > > A singleton group is just a multi-device group that hasn't been > hotplugged yet. > > We don't seem to have the concept of a "true" singleton group which is > permanently single due to HW features. > > > This series aims to avoid conflict having both user and kernel drivers > > mixed in a multi-devices group. Well, the difference is just in literal. I don't know the background why the existing iommu_attach_device() users want to do it this way. But given the condition in iommu_attach_device() it could in theory imply some unknown hardware-level side effect which may break the desired functionality once the group size grows beyond singleton. Is it a real case? I don't know... You are now redefining that condition from singleton group to multi-devices group with single driver bound. As long as no object from existing driver users, I'm fine with it. But still want to raise awareness as it does change the existing semantics (though might be considered as an imperfect way). Thanks Kevin _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu