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dkim=none (message not signed) header.d=none;intel.com; dmarc=none action=none header.from=nvidia.com; Received: from BL0PR12MB5506.namprd12.prod.outlook.com (2603:10b6:208:1cb::22) by BL1PR12MB5256.namprd12.prod.outlook.com (2603:10b6:208:319::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4544.13; Mon, 27 Sep 2021 15:09:29 +0000 Received: from BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::e8af:232:915e:2f95]) by BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::e8af:232:915e:2f95%8]) with mapi id 15.20.4544.021; Mon, 27 Sep 2021 15:09:29 +0000 Date: Mon, 27 Sep 2021 12:09:28 -0300 From: Jason Gunthorpe To: "Tian, Kevin" Cc: "Liu, Yi L" , "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 Message-ID: <20210927150928.GA1517957@nvidia.com> References: <20210919063848.1476776-1-yi.l.liu@intel.com> <20210919063848.1476776-7-yi.l.liu@intel.com> <20210921170943.GS327412@nvidia.com> <20210922123931.GI327412@nvidia.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?vBkYur2JhgJ/hMToyO0s4HO+hBqSqURnJ0tpVwfVlVnds0047ym/ZcADDbM7?= =?us-ascii?Q?FIyhU3a8/YfL2sLBDBYkHFXRETeZGz1oewxF+B/QcOFxJ4J7vyAwdNRynC5S?= =?us-ascii?Q?QXrCluJsQmIoWJWcX0x1ajJe4uEF1ZL5ytILWrtzFDg9Q6GXHxWZk1601rqX?= =?us-ascii?Q?ki9ClW37lSDKPIiPXS7iFupV3glcO4pINmxFeHQp/5QvnfHYIxWp9dzRe8ib?= =?us-ascii?Q?00H9y5bDMA4iN71YCklRCYLDw+AHSgJKfiYMj7Evyt2MabbqvVaVc9R1xqPA?= =?us-ascii?Q?FxhSURZmuLPFknoaCgur641FZSexhtgMayB17EGY2d+vsT4VjuQiWcEuGC2/?= =?us-ascii?Q?18fXq8SO3z53yFQlfkmcHD7xetn9kMq9juKTgklU1l5yhhSoRz/YpSqed7J7?= =?us-ascii?Q?XQ0/kLezl5lTqBjCwbIrrzpEPInIhVpVSutXOVQHkwBZurWPd4mKG28QNban?= =?us-ascii?Q?JOWrgKPCP5vTiNcNa8CHYbSn8A696I19EK2Xuo/Nb3OoHiMgY+MBr+ZWKrbl?= =?us-ascii?Q?/6r+tuD0HmzaHdr9nhQrYT9MO4taCs+AXM2ce5vvxp5c6UzKfwTApDT4vEXh?= =?us-ascii?Q?bwX6iIxds8wkf8U1ElyJkz+b6YTzMYDdPx4GBvDKlrdec3ooqRd7X6LcewdF?= =?us-ascii?Q?6MgFEgLK0+M9koLCut+84QWzA5gekerj5r0M4he23XJpsdEtglTu9m8QQvQW?= =?us-ascii?Q?AA3Fp7pVYV6XJlItTmUhJlBDVeJh1t6Ai/M5T1iqEbHKs274B2SHGkbDZccV?= =?us-ascii?Q?Twl82iYShjarV8+J/4f0W+usko2g2ypyv4Nl+b9PJvTMoEwksRtEDkp6sNvl?= =?us-ascii?Q?6hvb2rlgc1IHdfER/3P1xvnp8EG2bU6n8UHMvhkSjiql8Dd5iutdbA0D8Rbm?= =?us-ascii?Q?LpgIuzaVFxFzFgbusVu3m6OFjfPWc0DVzyqdd7GBoF/EgtCYp7b1GMYYGakI?= =?us-ascii?Q?hfC+vtaW1hGcskJeW+bVbihX7Tu+QKxL8Kl0PY0EgOYHIb5X2hE7aZ6GORMc?= =?us-ascii?Q?JiXTGRzAmN0NehCmNTYJL/aNczn9CC1aq8vOzHx+51af1KsXPuHvJ++/pwrh?= =?us-ascii?Q?DUXdYRcMYmwvB7kNSriZ0R1zTnRTWSAWFN/DSd04IK9roZMW+SS16V40BmY6?= =?us-ascii?Q?boBEc8mDZ39QPUcHgwis/Y/IRNkS3eMSTbmXc/MBZJE77oWICP8EBG2MMDW3?= =?us-ascii?Q?apg66IzJjZAPOuYjTAoHDXic5aWzFgzFCgryyDvEW0CYE0EL46/C3YFvZb6G?= =?us-ascii?Q?H1L3ptatFymUuL7ZvdwItOp3eu09IZmahGHGyOmzGzZIjOTUvFTKCYLPzRdL?= =?us-ascii?Q?5AN9T8R7YuDFonvNmo7SoknH?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 5ae576e4-c0a7-4e0a-a3d3-08d981c8cd85 X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Sep 2021 15:09:29.4859 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: BFQQ/A8stHEOkF7pH4AZF9U5kn0D98sooG1SX1gFNjL9oV9UHaKqdnXSDMR4ggqg X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5256 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 27, 2021 at 09:42:58AM +0000, Tian, Kevin wrote: > +static int iommu_dev_viable(struct device *dev, void *data) > +{ > + enum dma_hint hint = *data; > + struct device_driver *drv = READ_ONCE(dev->driver); > + > + /* no conflict if the new device doesn't do DMA */ > + if (hint == DMA_FOR_NONE) > + return 0; > + > + /* no conflict if this device is driver-less, or doesn't do DMA */ > + if (!drv || (drv->dma_hint == DMA_FOR_NONE)) > + return 0; While it is kind of clever to fetch this in the drv like this, the locking just doesn't work right. The group itself needs to have an atomic that encodes what state it is in. You can read the initial state from the drv, under the device_lock, and update the atomic state Also, don't call it "hint", there is nothing hinty about this, it has definitive functional impacts. Greg will want to see a definiate benefit from this extra global code, so be sure to explain about why the BUG_ON is bad, and how driver core involvement is needed to fix it properly. Jason 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 7B753C433F5 for ; Mon, 27 Sep 2021 15:09:36 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 F23666101A for ; Mon, 27 Sep 2021 15:09:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org F23666101A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lists.linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id BCD2F6081B; Mon, 27 Sep 2021 15:09:35 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id iRUln_FSuXEv; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Mon, Sep 27, 2021 at 09:42:58AM +0000, Tian, Kevin wrote: > +static int iommu_dev_viable(struct device *dev, void *data) > +{ > + enum dma_hint hint = *data; > + struct device_driver *drv = READ_ONCE(dev->driver); > + > + /* no conflict if the new device doesn't do DMA */ > + if (hint == DMA_FOR_NONE) > + return 0; > + > + /* no conflict if this device is driver-less, or doesn't do DMA */ > + if (!drv || (drv->dma_hint == DMA_FOR_NONE)) > + return 0; While it is kind of clever to fetch this in the drv like this, the locking just doesn't work right. The group itself needs to have an atomic that encodes what state it is in. You can read the initial state from the drv, under the device_lock, and update the atomic state Also, don't call it "hint", there is nothing hinty about this, it has definitive functional impacts. Greg will want to see a definiate benefit from this extra global code, so be sure to explain about why the BUG_ON is bad, and how driver core involvement is needed to fix it properly. Jason _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu