Received: by 2002:a05:6a11:4021:0:0:0:0 with SMTP id ky33csp75317pxb; Tue, 21 Sep 2021 19:12:26 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzcrCVYKozSMN6oAh+IIeSafCvNyzd6kobFgx/Y5Odbbt8AbbyqqJjdHewITxXNk5hWPcUe X-Received: by 2002:a05:6638:1909:: with SMTP id p9mr2728251jal.108.1632276746745; Tue, 21 Sep 2021 19:12:26 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1632276746; cv=pass; d=google.com; s=arc-20160816; b=dyhAtfhBODDd7yy6BGJwT71blD4bcDegMPcmUylbU2m3Blerxgm1aZXGx8Dz37tNQc LA9LHuI2iKqJAUlHJaibaUDWE7hLNE93jzi1jxyUei4n33LJI1QcAxZrJ3/g43jhCMir lMJjlNor6B0dXFWAkE6SARZ3m6v8eho3YpcnD9YyYGeZwU0XGBCJojwk8SmcHfpIyaxe FqbShP2OevOIVN9c58zvkMLpvYyvyiOUGLiYAlzhyH3xJ2lWRhSvKyjPjhAZJdAZhlpc Va87MVa0exBThzACZG2fC3+oVVnarlMfnaDHA19YLSyp+dVemtuB2G9e7oSFNFBD7Wnm +1MA== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:content-transfer-encoding :content-language:accept-language:in-reply-to:references:message-id :date:thread-index:thread-topic:subject:cc:to:from:dkim-signature; bh=m4TOPmWR8lW/r/VEwSsHVBVCre0YwCYuee4w7xDVgW8=; b=UPqhfi+J/D5GMvn/MSn5sLElyMTUqEx6bQRcRH3HEhYcVP11NUPMfTtB+Xcb5/JqiG +/cF/lBoo3Sbvde4xLz0t+DGADbG7hs3gFRt3sW0msbFt+I98vydhb3F09bgpew+z3Rd 60oU/eHVKn8g8Wx3SpvFfosZHLAObYbWt2JQpaPvjC/zU1CLZd8tIARyR9SHG7E4Vd+z zNCx2RMuwKLd/gHLcmLP/xAiz2HT9Qc8q+0PAMg6anzC+WN+z1wMTOgDnMjDeCUQw8oz ymP1fB2dDEpLzhP+LTWA2YBUdOW0TbdW3bk87zaTCH5YNCQjH/G9EQxa0aojDsN4TxL8 5/qw== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@intel.onmicrosoft.com header.s=selector2-intel-onmicrosoft-com header.b="A/Cfk21A"; arc=pass (i=1 spf=pass spfdomain=intel.com dkim=pass dkdomain=intel.com dmarc=pass fromdomain=intel.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Return-Path: Received: from vger.kernel.org (vger.kernel.org. [23.128.96.18]) by mx.google.com with ESMTP id r4si1056265ilb.106.2021.09.21.19.12.15; Tue, 21 Sep 2021 19:12:26 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@intel.onmicrosoft.com header.s=selector2-intel-onmicrosoft-com header.b="A/Cfk21A"; arc=pass (i=1 spf=pass spfdomain=intel.com dkim=pass dkdomain=intel.com dmarc=pass fromdomain=intel.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232523AbhIVBsj (ORCPT + 99 others); Tue, 21 Sep 2021 21:48:39 -0400 Received: from mga09.intel.com ([134.134.136.24]:21502 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229834AbhIVBsi (ORCPT ); Tue, 21 Sep 2021 21:48:38 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10114"; a="223529701" X-IronPort-AV: E=Sophos;i="5.85,312,1624345200"; d="scan'208";a="223529701" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2021 18:47:08 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.85,312,1624345200"; d="scan'208";a="474383004" Received: from fmsmsx606.amr.corp.intel.com ([10.18.126.86]) by fmsmga007.fm.intel.com with ESMTP; 21 Sep 2021 18:47:08 -0700 Received: from fmsmsx612.amr.corp.intel.com (10.18.126.92) by fmsmsx606.amr.corp.intel.com (10.18.126.86) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12; Tue, 21 Sep 2021 18:47:07 -0700 Received: from fmsmsx605.amr.corp.intel.com (10.18.126.85) by fmsmsx612.amr.corp.intel.com (10.18.126.92) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12; Tue, 21 Sep 2021 18:47:07 -0700 Received: from fmsedg602.ED.cps.intel.com (10.1.192.136) by fmsmsx605.amr.corp.intel.com (10.18.126.85) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2242.12 via Frontend Transport; Tue, 21 Sep 2021 18:47:07 -0700 Received: from NAM11-DM6-obe.outbound.protection.outlook.com (104.47.57.170) by edgegateway.intel.com (192.55.55.71) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2242.12; Tue, 21 Sep 2021 18:47:07 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=be0udcKCpD7V8syjT+VobvG5JBaSjZksjL0YUaN5eGQvAMugN9brzPGwnF4R0wf9QnR2+Q8i0oIyxLnd61KjgyFsPlQ4EuV1C/DkQMmjxiLyv2+gpdwLxNNRaq7zUqPfj4TjylyZUq5uvdkqu3Fhz6lUGqm7/C5URBdImAJeOsY0lZ+5rigmEEVtRV5AIhrxGpOigjVJG+CmnaoAJzXag3tIV+gMvfYOnRpg+CZ4RRVa8B6F3qvt203KtTXAq0CeLKhk0UXeEInQ2Iuv6O71LbXF4qhQ9BjVJ/+7JYt3iReOtxKApkOhe03QozyMC3+RP5APIHH5lVoz/rHNK61bgg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version; bh=m4TOPmWR8lW/r/VEwSsHVBVCre0YwCYuee4w7xDVgW8=; b=ZVCkcjDB4ZF9/Me6K2HNbh8OKg3wW0W5Outa3zMEat8uefks42DgGKVWxBVkqVickq2wSJcWinKtjTDHHrJpyZO0F3aX6Uu6G9WN1Z3DJs5ZYfhkyt8O/VcyGVxgRzmsP3fGUfuoFTqsDkP33brMvEHT3EpwW+7f0pzuuz4fi7BWWseSN7+OtsoVwimGVlePwed+Nzdxq9iuhBJUViysu7sZ26zGeVA+MshPE4ZfcLqWrnhaMuqvL73UAvHBEPmibC+QO71oAAOiTLDfutGJrDz4xUPzZzqAL3xkl4H6yVLyypdkmY3azatfc/b5MzycgS0c4bZ4TDeSU7FGzMy7dQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel.onmicrosoft.com; s=selector2-intel-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=m4TOPmWR8lW/r/VEwSsHVBVCre0YwCYuee4w7xDVgW8=; b=A/Cfk21AepuzmWMxmolVeYI113AMiwFwn3ZS5/S5i1rzMNxmr1QIYNzhBXvHsAXikYEgNeusZ7SYP4XGtMcqDAw7N6UjT9p0y4uOAB/RARf/7NN8WfKyVLCKoxorNxeRPsnuVBN5w9jGNpgzXmfoUC8ohv2HPoK2D/7L8HoRPUs= Received: from BN9PR11MB5433.namprd11.prod.outlook.com (2603:10b6:408:11e::13) by BN6PR11MB1332.namprd11.prod.outlook.com (2603:10b6:404:48::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4523.14; Wed, 22 Sep 2021 01:47:05 +0000 Received: from BN9PR11MB5433.namprd11.prod.outlook.com ([fe80::ddb7:fa7f:2cc:45df]) by BN9PR11MB5433.namprd11.prod.outlook.com ([fe80::ddb7:fa7f:2cc:45df%8]) with mapi id 15.20.4523.018; Wed, 22 Sep 2021 01:47:05 +0000 From: "Tian, Kevin" To: Jason Gunthorpe , "Liu, Yi L" CC: "alex.williamson@redhat.com" , "hch@lst.de" , "jasowang@redhat.com" , "joro@8bytes.org" , "jean-philippe@linaro.org" , "parav@mellanox.com" , "lkml@metux.net" , "pbonzini@redhat.com" , "lushenming@huawei.com" , "eric.auger@redhat.com" , "corbet@lwn.net" , "Raj, Ashok" , "yi.l.liu@linux.intel.com" , "Tian, Jun J" , "Wu, Hao" , "Jiang, Dave" , "jacob.jun.pan@linux.intel.com" , "kwankhede@nvidia.com" , "robin.murphy@arm.com" , "kvm@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "dwmw2@infradead.org" , "linux-kernel@vger.kernel.org" , "baolu.lu@linux.intel.com" , "david@gibson.dropbear.id.au" , "nicolinc@nvidia.com" Subject: RE: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Thread-Topic: [RFC 06/20] iommu: Add iommu_device_init[exit]_user_dma interfaces Thread-Index: AQHXrSF9WDj+Z+DU+UqMJ7tQK2EdmauuvK2AgACKnbA= Date: Wed, 22 Sep 2021 01:47:05 +0000 Message-ID: References: <20210919063848.1476776-1-yi.l.liu@intel.com> <20210919063848.1476776-7-yi.l.liu@intel.com> <20210921170943.GS327412@nvidia.com> In-Reply-To: <20210921170943.GS327412@nvidia.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: nvidia.com; dkim=none (message not signed) header.d=none;nvidia.com; dmarc=none action=none header.from=intel.com; x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: b08020ef-4d3f-45f9-9dac-08d97d6ae18c x-ms-traffictypediagnostic: BN6PR11MB1332: x-ld-processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BN9PR11MB5433.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(71200400001)(55016002)(316002)(508600001)(8936002)(66446008)(186003)(38070700005)(76116006)(83380400001)(7416002)(7696005)(26005)(9686003)(122000001)(8676002)(33656002)(110136005)(54906003)(2906002)(4326008)(66946007)(64756008)(5660300002)(66476007)(66556008)(6506007)(52536014)(6636002)(38100700002)(86362001);DIR:OUT;SFP:1102; x-ms-exchange-antispam-messagedata-chunkcount: 1 x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?r4GBbGiHWWjWUu882pPvlN3jbNY4Yb11MsxEf0n2HZjPkeLyCMCdUsyAKoD2?= =?us-ascii?Q?hYD3mrwFeMowY9newYl6gnRPyQ1jnIoh9jHvlXqyi4HjyvPK7anvtaa3TsBn?= =?us-ascii?Q?C+xzU3DtSZYq8QNJJft9XSMV7siJcY53wE+yls0++lrei4nb+iwWN0Dz9LRe?= =?us-ascii?Q?oZ3UslhrDsoWROPwaC/Wjz/o8mc2TOvp/aVsUhfn05it/TXg118RBQPCFyFk?= =?us-ascii?Q?3/Wr8nUeezg6uRJbiCna2tz/dEwZCDnxXx3lS9eOPh7qrjlkF1KIdWr0jwon?= =?us-ascii?Q?AHR0d/3Supy/wHaU8oEuENGFeXDQzu15HDizh6x9ep4woqhAGKJrPi7/Tot8?= =?us-ascii?Q?EjsFkcDtD85F4O0cFFWg0JkliUB1/dSxmJpMpWpO9s8if9yayI+0wPpbQev+?= =?us-ascii?Q?IO+PW/lJOOIgPlzJ6QHSHJCfdPZ7Tnt2TMadQTnxsqEMCuIODZlSPcHIgvhH?= =?us-ascii?Q?eW3ZC/kvAZFE2isBrAViTdst2KTbItTIPVNvmw3hO9cn5yD4Yxmyckjw2VSR?= =?us-ascii?Q?jap+sBfsdHB6dQ4iulZZY7OIqSuO8weoJzt/xoQTyO3fIFBeYixonIP5x6f9?= =?us-ascii?Q?Irzh1mrn3KGfgyK+oo0PBafYzxxR3s9zP7AVwtOY7B3jy/VbzJIYGwU1uN3A?= =?us-ascii?Q?JYcaSiPeCp/cQXT+D1fBgl3oFp3Oj8W9ZRlIcE+q7gmKaohm8eKdNzbFiZqr?= =?us-ascii?Q?aA5KJSq7mEh4UmC2UHZEJDqIbX+nT1Ors5ndIHlkryf8qHXdSIyEPzmomord?= =?us-ascii?Q?U+18VSdhswsIJo0Wc11iA1I96xdVRQYacCklRD/V7un+NHL0n/kYkREdH7fA?= =?us-ascii?Q?Mn8W1xneNE2BJ/ASoNinIbtQPUNur4S8MnCjeHgp7ShKTDoYMrzGTXCXJJBZ?= =?us-ascii?Q?TisWbsxV+4G/BQ26/g2gh6CMWiZK9xhI+rDffp0Fs0s3a0/6hYO1PsBZdbHj?= =?us-ascii?Q?F2QAcMMVDDn6bsYJHLdzhBbgfZq0uMOs10RmxkN0UPtgpxoFf6aLwwJdpUhB?= =?us-ascii?Q?flLOJMjnmp1ZG7NGc36OM3m6kU3s4OiZ1eJUrOMM03R4jeESu0g4+8iO1c0B?= =?us-ascii?Q?EaxvUp5ytzEvybEqTpUKPn8kkzlZ0Rcu0KH2exKa7fG8ucrrg0FVSFZSKkAA?= =?us-ascii?Q?OclapYqBmPoznUTJiVhB+TOAI9pw+betH5gUKemvGCZCUNOpBfR2gE9HO73p?= =?us-ascii?Q?FOdnwmS+KDyG9SZAuCVNumK8kJ7cZ8dhOp3BvEdsgEOy6kI5fPLiT5de8M86?= =?us-ascii?Q?YCXu22atdi7UkqyFT2ewS+0YjjKiCmttj771dG9ZUAeDyVlJWOXTDijX6Q5z?= =?us-ascii?Q?QI/0MG5WtC1DwQyKEO/y7Iye?= Content-Type: text/plain; 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: b08020ef-4d3f-45f9-9dac-08d97d6ae18c X-MS-Exchange-CrossTenant-originalarrivaltime: 22 Sep 2021 01:47:05.1485 (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: 4EU+hHHlCN5AnswMpEqHqZ9FkFcXmZDvtkF6oYEAVtHfIvBS9CakqY3OSpB1fp2WX9WxKntsZ7BF3TbFk/ZANQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN6PR11MB1332 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Jason Gunthorpe > Sent: Wednesday, September 22, 2021 1:10 AM >=20 > On Sun, Sep 19, 2021 at 02:38:34PM +0800, Liu Yi L wrote: > > From: Lu Baolu > > > > This extends iommu core to manage security context for passthrough > > devices. Please bear a long explanation for how we reach this design > > instead of managing it solely in iommufd like what vfio does today. > > > > Devices which cannot be isolated from each other are organized into an > > iommu group. When a device is assigned to the user space, the entire > > group must be put in a security context so that user-initiated DMAs via > > the assigned device cannot harm the rest of the system. No user access > > should be granted on a device before the security context is establishe= d > > for the group which the device belongs to. >=20 > > Managing the security context must meet below criteria: > > > > 1) The group is viable for user-initiated DMAs. This implies that the > > devices in the group must be either bound to a device-passthrough >=20 > s/a/the same/ >=20 > > framework, or driver-less, or bound to a driver which is known safe > > (not do DMA). > > > > 2) The security context should only allow DMA to the user's memory and > > devices in this group; > > > > 3) After the security context is established for the group, the group > > viability must be continuously monitored before the user relinquish= es > > all devices belonging to the group. The viability might be broken e= .g. > > when a driver-less device is later bound to a driver which does DMA= . > > > > 4) The security context should not be destroyed before user access > > permission is withdrawn. > > > > Existing vfio introduces explicit container/group semantics in its uAPI > > to meet above requirements. A single security context (iommu domain) > > is created per container. Attaching group to container moves the entire > > group into the associated security context, and vice versa. The user ca= n > > open the device only after group attach. A group can be detached only > > after all devices in the group are closed. Group viability is monitored > > by listening to iommu group events. > > > > Unlike vfio, iommufd adopts a device-centric design with all group > > logistics hidden behind the fd. Binding a device to iommufd serves > > as the contract to get security context established (and vice versa > > for unbinding). One additional requirement in iommufd is to manage the > > switch between multiple security contexts due to decoupled bind/attach: >=20 > This should be a precursor series that actually does clean things up > properly. There is no reason for vfio and iommufd to differ here, if > we are implementing this logic into the iommu layer then it should be > deleted from the VFIO layer, not left duplicated like this. make sense >=20 > IIRC in VFIO the container is the IOAS and when the group goes to > create the device fd it should simply do the > iommu_device_init_user_dma() followed immediately by a call to bind > the container IOAS as your #3. a slight correction. to meet vfio semantics we could do init_user_dma() at group attach time and then call binding to container IOAS when the device fd is created. This is because vfio requires the group in a security context before the device is opened.=20 >=20 > Then delete all the group viability stuff from vfio, relying on the > iommu to do it. >=20 > It should have full symmetry with the iommufd. agree >=20 > > @@ -1664,6 +1671,17 @@ static int iommu_bus_notifier(struct > notifier_block *nb, > > group_action =3D IOMMU_GROUP_NOTIFY_BIND_DRIVER; > > break; > > case BUS_NOTIFY_BOUND_DRIVER: > > + /* > > + * FIXME: Alternatively the attached drivers could generically > > + * indicate to the iommu layer that they are safe for keeping > > + * the iommu group user viable by calling some function > around > > + * probe(). We could eliminate this gross BUG_ON() by > denying > > + * probe to non-iommu-safe driver. > > + */ > > + mutex_lock(&group->mutex); > > + if (group->user_dma_owner_id) > > + BUG_ON(!iommu_group_user_dma_viable(group)); > > + mutex_unlock(&group->mutex); >=20 > And the mini-series should fix this BUG_ON properly by interlocking > with the driver core to simply refuse to bind a driver under these > conditions instead of allowing userspace to crash the kernel. >=20 > That alone would be justification enough to merge this work. yes >=20 > > + > > +/* > > + * IOMMU core interfaces for iommufd. > > + */ > > + > > +/* > > + * FIXME: We currently simply follow vifo policy to mantain the group'= s > > + * viability to user. Eventually, we should avoid below hard-coded lis= t > > + * by letting drivers indicate to the iommu layer that they are safe f= or > > + * keeping the iommu group's user aviability. > > + */ > > +static const char * const iommu_driver_allowed[] =3D { > > + "vfio-pci", > > + "pci-stub" > > +}; >=20 > Yuk. This should be done with some callback in those drivers > 'iomm_allow_user_dma()" >=20 > Ie the basic flow would see the driver core doing some: Just double confirm. Is there concern on having the driver core to call iommu functions?=20 >=20 > ret =3D iommu_doing_kernel_dma() > if (ret) do not bind > driver_bind > pci_stub_probe() > iommu_allow_user_dma() >=20 > And the various functions are manipulating some atomic. > 0 =3D nothing happening > 1 =3D kernel DMA > 2 =3D user DMA >=20 > No BUG_ON. >=20 > Jason