From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from BN1PR04CU002.outbound.protection.outlook.com (mail-eastus2azon11010014.outbound.protection.outlook.com [52.101.56.14]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E65EC3F23B4; Fri, 24 Apr 2026 18:30:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.56.14 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777055413; cv=fail; b=UzMkTm0oNIAFEtrQYJaa2ITYP8uyanB5S7t4F+dtpexHttre7etG4z7yBKdAlzbHCxPturCcisd+FJfWiRhB2NyW3Bhw3S6BoBBxgdaNVyVIb71JrXaJFm3QVTRa4ntAR21+Jv3GoQ7dZ3y3yZIrFVJIwaUXOXR9Fv78FphFjvk= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777055413; c=relaxed/simple; bh=Vd1WD74hgmeh5j9RILuodBhxdRkT9bdBPlM1uUZ3tIU=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=HjRlrX+vU25eiT8pkK2q1LpPdSJfLJHKF7Er2Nx/iVzlhMKGp9XY6sAB4gMKcqo/L1ljc2fTcKquXWIAq9EQ8FGliceRRTBBbntLUfLyOjtkNRYNy5442uYkbV9AtQ/OIBoWTLa6NtlZf6z2oNH5JMYFBr1751hcB4cuN1GoyK4= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com; spf=fail smtp.mailfrom=nvidia.com; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b=pQvTAFhY; arc=fail smtp.client-ip=52.101.56.14 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=nvidia.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=nvidia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=Nvidia.com header.i=@Nvidia.com header.b="pQvTAFhY" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=vOVmZ978wVuIfnrf5ojCP/oy8Uw+YegAGcGScPfcQqVrmxx6xgX2OzydbxEAbGpyc/H7Qu/ikZTKZkGouQioozJnMdtYu7OtKaqm/I0AiQ4A/Wur3gS6VEiqoRpMWL83yj7uPsH0g7FAvvEjh9veviREQd0dG9rgZjinqvDkPrOMe7B/kgZBlKHebpD2PH1N9S3BFtektDkjgcCYncIWfDajbCSjrt78VBUOvGBwiPDai2rCa7h84pYpnj7OPMPRc0qTZlHEXSJV09JoLAo2tYjn2zQBweBJlZsaUbzgUY1Tb6fpeK41BqKWRktvXi0DMqkwnbMLr74iiM8WF4uvog== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=B28cUMDLN8YrvhvAvPQ+2rKU89qh6QRfjUVRKyn4U2U=; b=lI0FJCgNVEvYEjps7thuADz1MpwLNG4zvhelXUe3U/IGfpR39knKwQq6qXmMsuQ7RQBvSMR9vcR/8EOaF11PEu2QD5ldjkHFdW4L9n9S39rgSDYH5byZAC1mtjlYdDdmMcdg8eW5oFVO4DJlxI/JY5BanShFTbx6yYIBOTfgBfzZNkLkx5Q0rPWfyR70gIydfEiRsCQZOEeYznmv4ilxSdlK5PdEJJxzuwhC9fB3fUPnKVZdJV2icKxpY1ZnJTO4LGCdXYsEH/prDdCvCDHjQBMRp4sDewNkF2KIU6R821fkaKfu/CQPDWX0tWDZ/WC0AXO0FPYtXDLLxJjuB6Yshw== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=B28cUMDLN8YrvhvAvPQ+2rKU89qh6QRfjUVRKyn4U2U=; b=pQvTAFhYN32CATg4HERUvi3xvxPdzQTEeZ9pDV9TvLzK3sf/kQsgRxtFYn6RFizDJH/rlEC1pV5eaSiBehFVACBIqw7FgXezmmPvvUYW2raGQEMRAo/0GlaliZbNOLKzjLFeI9A9rUmnHCNvAuE89jkH0jzgr70Ft8zlLZEI2/eyXB5JsCvcbU1L2Ir/HRdHbBG1gkqbNMRIARAPL3Zr+hOuQ4sJua0lBVnn7e5lGvGrqR/tKSWKZyG8XyJUpCoJov0v31XRUAbMZDlcR6RAbCtVGraIiTyR6SXKeL2agvcaVoWxowMxGvK7Y6hEkAxBZkIqANpxZEqumDJMosv6NQ== Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nvidia.com; Received: from LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) by BL3PR12MB6476.namprd12.prod.outlook.com (2603:10b6:208:3bc::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9846.21; Fri, 24 Apr 2026 18:30:07 +0000 Received: from LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528]) by LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528%5]) with mapi id 15.20.9846.019; Fri, 24 Apr 2026 18:30:07 +0000 Date: Fri, 24 Apr 2026 15:30:06 -0300 From: Jason Gunthorpe To: Matt Evans Cc: Alex Williamson , Leon Romanovsky , Alex Mastro , Christian =?utf-8?B?S8O2bmln?= , Mahmoud Adam , David Matlack , =?utf-8?B?QmrDtnJuIFTDtnBlbA==?= , Sumit Semwal , Kevin Tian , Ankit Agrawal , Pranjal Shrivastava , Alistair Popple , Vivek Kasireddy , linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, kvm@vger.kernel.org Subject: Re: [PATCH 7/9] vfio/pci: Support mmap() of a VFIO DMABUF Message-ID: <20260424183006.GI3444440@nvidia.com> References: <20260416131815.2729131-1-mattev@meta.com> <20260416131815.2729131-8-mattev@meta.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260416131815.2729131-8-mattev@meta.com> X-ClientProxiedBy: YT4PR01CA0084.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:ff::9) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|BL3PR12MB6476:EE_ X-MS-Office365-Filtering-Correlation-Id: a1bf26df-b98b-4312-f9c4-08dea22f8297 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|7416014|366016|18002099003|22082099003|56012099003; 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:LV8PR12MB9620.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(7416014)(366016)(18002099003)(22082099003)(56012099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?3UM6ziRBrV963GEkflIQjj0s4/9LNCmkm794pF1lSfFMJQvF76QTzITd6Fdo?= =?us-ascii?Q?h1tdVC36Aq6sp+1ko9DUGnOXvEnsEr6XO8P7adDM39HxzmwJ/ZTTJ4JJYYuq?= =?us-ascii?Q?4DCIP+PFpBkmlPF6q2DMZ9J01AfCyRnqbGtJTUPPC6HkYZ3xGkVLXRpzxuz3?= =?us-ascii?Q?oVcqPSbTEFv8TMH+KoUGIME/uLR8hcFa+/CqPTcUDsL2s0NIQNP6iJ/32HmI?= =?us-ascii?Q?fCHnoD0+vVE7G/VyevukcaB6NOSVMiJxw5dVP0ov0ajietXt0TQgl2mjglfp?= =?us-ascii?Q?AOjgvc8c0sfPWR49sUAIbwrJtWzWLNGBdOKieBvOJlMv7qylEJoNaGBtz8GV?= =?us-ascii?Q?RjNrge5+xPeNP/wW0VkEpxmGs4Ci1d+RxoTOBRRKyqChbiCvuIWdTF5wzyLh?= =?us-ascii?Q?3kfsT13hLCa8eOa3RrRf3sdk0X15UrPHi1Af00Nvbz99uuZdLgCMulcRxyr4?= =?us-ascii?Q?OoKZ1cgYaz0z2UJ+TQolIDMBVSl3vW2ZLk7l+tPBQrDSQloKNrZum5YRx4dc?= =?us-ascii?Q?kNMhmUJAw0UUN+ukbKYbAvH4AVXEVYQ1cAmqpvhcSLXKizkW7khCBRAztMn9?= =?us-ascii?Q?YdfEC2tFxkdMUFAiaHwTVA4hJyCCDBr+YP4wx8GbL5YIN5+eHTYGB7uu1o9N?= =?us-ascii?Q?BVGLpJh313JUcPOwBHSO9RODmdyZCpfVZEmzWxu2T9/gubE7Ivpg+2PVfaAh?= =?us-ascii?Q?ObQr4qu2oAsrKtWhR5A3UQApTfEJu09AGse4urnXFe06kNR8MbvcOrcBmyi0?= =?us-ascii?Q?3t0VyZAcjV5kOYT9UqI8B/jFnSxIWIPN+VA/nM/8HXq7jN0RYPUZq4PTm1oB?= =?us-ascii?Q?wTw54Xbe5b9UB462Qf6f+gIcrSTCD0q040kCApkGyWlHBPuAhJzFrOZ8UqYM?= =?us-ascii?Q?FLejxCiEhxVb2LZ0qYFsEZrTDvywY9jtGGUmeqqgad/tWZpFcoI2JIGSC34u?= =?us-ascii?Q?OSbSW9T02x+xRCErjVGVOYsQfq24WzxIKjompWawDROgTy6WPiJtBHmGfT0G?= =?us-ascii?Q?k4nCa+FZxLe759mKjMqtbIE/Vv9m3ntND5a8FVYgENGxOmpi4ObhJs1p7YA0?= =?us-ascii?Q?dOgFIqJvHaXlP93OMg5T5WIWGdlsSm9igQCPamx2OU2Vtk449d5rMDhcYvCE?= =?us-ascii?Q?/pb8Nb7pk4xi0gJXU+8veA4rldM1ShN2xIMZULRdSi5UrJdt/cXPdlZKiWns?= =?us-ascii?Q?wdZYHN5+9wQzd6Dzo11VqmqbL4vnM4uaTseFn6CuqflD7tn0azZgInh6h4+0?= =?us-ascii?Q?JfEun8Ks15y0SapT2qbLwdcGKY/iqcezZlsw1jcGZThB80yffs9F0KFsa3zw?= =?us-ascii?Q?0alsTnh61C1vwuDTutHj+3LUfu8Rmf9xfmfcI+KNQb7on6Nlwz/sx9WMogbh?= =?us-ascii?Q?sEeFKDmmi3QWbW5FsO8BoN5MnmIdwzHlXwU2nj+QBf6mu16Ld1tsyAtodM4/?= =?us-ascii?Q?jpQ80Liriwzp4BdkqQ56iP0YnT3+skFW4SrNAn/aum4ttlc58Z7p5AafwXRv?= =?us-ascii?Q?O7OwcnS0sulHLwbxZSBZvhX2+Zk80vuFnKdkdfj8Kr94zGKyEC8J6p53Y4b8?= =?us-ascii?Q?HoZrCCGlGtfU5Vc8ZTo0u9NK/pHKaQL7A2D4QHi/5JpRY2jFigWMDvCI2BtA?= =?us-ascii?Q?rNaE2NLfHsiPbprC4mtiLais8kTRL4XOunl0aUCMdbi/Ugpx0W7jFyvnS+9T?= =?us-ascii?Q?b0Ab4OPOvK6o2vzjG9vtpPXWvj7Sdb7qJy7xrprdJNIY+Sqx?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: a1bf26df-b98b-4312-f9c4-08dea22f8297 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Apr 2026 18:30:07.3450 (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: vFPpJks+y0xGWjQrezqlmc2X/WtTCdK6eLsobOZ6O0TD+7dHrd7xk7fhYCMfgYV9 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL3PR12MB6476 On Thu, Apr 16, 2026 at 06:17:50AM -0700, Matt Evans wrote: > + > + dma_resv_lock(priv->dmabuf->resv, NULL); > vdev = READ_ONCE(priv->vdev); > > + if (READ_ONCE(priv->revoked) || !vdev) { Why is this read once? It is inside the resv lock so it is stable? > + pr_debug_ratelimited("%s VA 0x%lx, pgoff 0x%lx: DMABUF revoked/cleaned up\n", > + __func__, vmf->address, vma->vm_pgoff); > + dma_resv_unlock(priv->dmabuf->resv); > + return VM_FAULT_SIGBUS; > + } > + /* vdev is usable */ > + > + if (!vfio_device_try_get_registration(&vdev->vdev)) { > + /* > + * If vdev != NULL (above), the registration should > + * already be >0 and so this try_get should never > + * fail. > + */ > + dev_warn(&vdev->pdev->dev, "%s: Unexpected registration failure\n", > + __func__); > + dma_resv_unlock(priv->dmabuf->resv); > + return VM_FAULT_SIGBUS; > + } > + dma_resv_unlock(priv->dmabuf->resv); > + > scoped_guard(rwsem_read, &vdev->memory_lock) { > - if (!priv->revoked) { > + if (!READ_ONCE(priv->revoked)) { Same here, it is not read once since you hold the memory_lock it is stable. Jason