From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from SA9PR02CU001.outbound.protection.outlook.com (mail-southcentralusazon11013022.outbound.protection.outlook.com [40.93.196.22]) (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 E2DC1415B74; Fri, 9 Oct 2026 13:18:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.93.196.22 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791551934; cv=fail; b=qJ+kZOTamtjWgTcwraadrV/nIYpSS7uoedIv4BnxViBP6WYz7BYG7NM1p+jpCzI+0WRzsUweBHocktCnFIn29E0FtgQ+f437qCEYMX/Gt6qoVMYvPBIcVprJne8tozqcdoQx0fB3ZAJW8VAuANeTMmFPmvzIfAjnltuaD0W5B3Y= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791551934; c=relaxed/simple; bh=ZQ6mKaT1r0FbuB4l9OR15QXwePkJGtL/c/xMnKsdlsc=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=FvPvhg/ci4E44n0SBQ9071mH9qfGOih2j1d7UzAtxXIJRNhXTmASuMGAhZ+bz3pkNP5MdU2VbX3Hql6nT4rDwyauA13egIVAh0T7zQJAjQGGESALqWdnSxY5oWyB/Nh9J0x/xpZGqX5TFMDLBjIGMIsI6OIgBKZwyiYgejMkLQk= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=WD5nLple; arc=fail smtp.client-ip=40.93.196.22 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="WD5nLple" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=piQSne4VGp0vj4ViIHAcdqTuGl/KyNpNlgp/Mbwgj4RctQi/9A1WqxQlRHSeOGfZQedm9cYqlRH7w8DtCORGhzy31X7+mCchEruB4WGUY3hPSh4aQn/Ehuh0yMEiKan+EML8J3/wsWerwIr3ld3fEVLUZYLXRU3WZMrC1b3Xncpsl0siyVKwOBltHDX0eTvCSfkm52V4+yl9AjgKxnLyS5AqUSpzYvyWswVXmPRDKaKxeRAneMy4JI+LxTyyL4SAU4f2Qd9hMT1ySDysGPp/dascMlvA6yRVuUTQloqTuG/VWu64qt7Kt6/htcG5aClfMTm6eDEZ9dSsyEj14qaAiw== 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=w/4202yTBKXCmAmsvGcUvutf7DTYr225ntdG/+lchHE=; b=mRP/uqYwMgRUY+awZaRHGQa9fv4JnnikvV2yjJcRuTbwILxd9EwnqO63UnqO+d6hD+gctTgdbsEjZ5Bd7We43O2k8f2ZALTCSP/UqI0nlb12jI7wIg4P00Ejwt2v4YEmVh5Ik2bXyX94/t7Q9f6TjmygLdt7FuSv9+nDt3sSXd0ualCJsaDJUigzRYht0GqaIg02CTv2gTMx/CEVwMdJbUq230MLZDqzN8r375uO8zgo/dCkPLDQX6Ncq6sldZKzIfrfKmangOWdMtHhB2wDDBeC+6fY2ovPOVTBugdXjpC2F+dhr8FGNhABz5pSPbb7b4za88AiB55+Vr0VmhRoaQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=w/4202yTBKXCmAmsvGcUvutf7DTYr225ntdG/+lchHE=; b=WD5nLpleVoj++wymg6lq1by0BtIyuM2kmGvLwwTJ7vUl0gUZIZtDPfam3CRSr3PCNyklmym/QRx2B6epRK0hnLZASQBHhscQUTK12hT1RRHv/RosYZzea/x2b8ICOJfMA/MBfiSb/ltn0aRtMlOy4uIefjkPaLunY+mRl51/FO8= Authentication-Results: mx.microsoft.com 1; dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) by SJ1PR12MB6267.namprd12.prod.outlook.com (2603:10b6:a03:456::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.472.15; Fri, 9 Oct 2026 13:18:46 +0000 Received: from PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::ce69:cfae:774d:a65c]) by PH7PR12MB5685.namprd12.prod.outlook.com ([fe80::ce69:cfae:774d:a65c%3]) with mapi id 15.21.0496.010; Fri, 9 Oct 2026 13:18:46 +0000 Message-ID: <17cfee61-0255-42fa-8034-6131c989f27a@amd.com> Date: Fri, 9 Oct 2026 15:18:40 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/3] dma-buf: add a warn-only mode to DMABUF_DEBUG To: Jason Gunthorpe , Karl Mehltretter Cc: Sumit Semwal , Andrew Morton , Rob Clark , Jianfeng Liu , Diederik de Haas , Andy Shevchenko , Vinod Koul , Bjorn Andersson , linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org, linux-kernel@vger.kernel.org References: <20261005064133.7305-1-kmehltretter@gmail.com> <20261005064133.7305-3-kmehltretter@gmail.com> <20261009124259.GA13920@nvidia.com> Content-Language: en-US From: =?UTF-8?Q?Christian_K=C3=B6nig?= In-Reply-To: <20261009124259.GA13920@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MN2PR11CA0012.namprd11.prod.outlook.com (2603:10b6:208:23b::17) To PH7PR12MB5685.namprd12.prod.outlook.com (2603:10b6:510:13c::22) Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH7PR12MB5685:EE_|SJ1PR12MB6267:EE_ X-MS-Office365-Filtering-Correlation-Id: 9370dea4-944d-4de2-7e5e-08df2607d931 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|23010399003|366016|10067099003|18002099003|22082099003|3023799007|4143699003|56012099006|11063799006; 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:PH7PR12MB5685.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(7416014)(376014)(1800799024)(23010399003)(366016)(10067099003)(18002099003)(22082099003)(3023799007)(4143699003)(56012099006)(11063799006);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?czBsVzZoVU1SRit4QkVFMllkNHlmKy9FVWVaWkJENWVrbzVnKzZUdEVhaUEr?= =?utf-8?B?RjhvOTIwcFFYMm1vbUExUERySlU2bWRNTk9LYk52RXBsUDFURERTQWxOZytt?= =?utf-8?B?NzFtMFRFWm9EdXA5N1FCdmRaWmZjWXBFSm5acGhMdDRQMWhxeGNLZVlPTDdo?= =?utf-8?B?U1JUMW5HbVc3VHlVY3VVNE1LNEl5WHpjTVd5aVlZNjh2dkY4US9oZC9kYmE2?= =?utf-8?B?TnpxeXF3anljVS9LSjN4R0tPSzVIdS83cTU2RUxVWVk4azkrTTBGd1RqYld6?= =?utf-8?B?QW81S1pSc3V2LzY0MjluZE9uZzZlRnplSkhjbE5oYnVyVVp4MVIvNlFhT0tp?= =?utf-8?B?eXNQbzc5N3I2UjdEb3ZRR2lsaXQ3M2Nic2dwRHpkbnBkVGo0bnIycnppeml6?= =?utf-8?B?dHUyazdEYnVwVXRWY2xaN1ZQTlRld2RSLy96V1k1TEhwRWNhQ3AvT0JSSmdJ?= =?utf-8?B?NlJ0OW82bXc3VWI3VnF4Vi9TcU00a0p4MWZFZ241V2lQL2hYSlEwTW42YUJk?= =?utf-8?B?Nzk5MEwrdDVEWGNSUVFlejF0YTlISlZBbGMxcnNRSVlNUlNsSVMxQ01GSHlT?= =?utf-8?B?Vy9PZHhFeEpZTFBMaVFNK2Z2OG5ZQVIxY2ZOd3dMNnIyNkVKSkJzZUJiMjhQ?= =?utf-8?B?U1pHVUx0OGVDQkQrejRUd3p5L3ZoV29xSEZ4dDRiTEpGcEExSGJmNjFkaVJ4?= =?utf-8?B?empyVFlkbFFTbVNSVFdMMUVEQ0g3ZUd6UGRSRXBlQWZkWXQzSDM0eExkaDNh?= =?utf-8?B?TDJTNlFvTmtRMHAwUVZ5cDFqMlJMdE9ZUzVBZVg1T2ZwaVI1WGpHc05FZ2Zq?= =?utf-8?B?d09za0wvTEQ0dzdIRzVLNndQbXRXZmoxR0JrcEFJMkZPWFFkTlo5N05xYkNu?= =?utf-8?B?Z0dGUmJSQ01TVUQxNGtnNWZxWGtycmZKRWpvNW9DMVluU045bmRuY3EwcnJ1?= =?utf-8?B?ckNQQWJkTFN1TW9ZaklIcVdOSWhqUGN5Nm1ZY1FIZXZYSktUVFh3QWkyRGhh?= =?utf-8?B?eTVjWE93R3NIbS8xZklCRytlWW5CTGxnOEE3NE0zb1FvNDBhc0RhYmdHV2Vj?= =?utf-8?B?MGg2eFN6UEVMUlg1bWw5bUVzK2szWkNQTi83MmgvYnlOU1AzdXBhS2tJVENR?= =?utf-8?B?VFlNd29TKzk3U3VKcFpRbUhLeWZTbXJTcmxnN29kUExiU2JkM1lzdVcvSGVH?= =?utf-8?B?VlMwbWZ1cDJTbTZrSFhHVE5hUUpsVDRYTC9tMHU3UU8vZEJ0eHlybUsxU1pC?= =?utf-8?B?Zk4reGNnMUU5aU9ZS0tWVVZFbWJwLzNZMXdHc3ltVkdubloyU2RoYzU1bE11?= =?utf-8?B?N3RQa3U4ckxQUkUySHZ1Qk45YUpJMy9wVFFpb2tldDJQcjhhNGtJV3pkOTEw?= =?utf-8?B?N2U4bVNtaWd1Zm1nUXg1b3p6eWk2ZzgyOU5lenI1TmlIdjVjOFRBQVVONHpx?= =?utf-8?B?U1o2U1ZacGw2bU9CQ1JwMmkxakZJVVdGZm5hTTBOaWczTzd3aWRVRkxWM3Zi?= =?utf-8?B?cTRMR0dDRHdqZ29PaXY3VkFqOGlIbzE2bjVRKzZxUWZLS0tybWQ1dXZ4T1Br?= =?utf-8?B?aVp4ODU1b1FyYm9vQ0IxeVBGL1VwN1BtRWx1aUduZzlyNFh1YWYvZ21NeTQ4?= =?utf-8?B?Zm9jNkNaa0RQODZhWnloeFY3MXBkY2V6ZUJwYnUxeEN1U0tNU0RBdy9Gelo1?= =?utf-8?B?SE04N2hsQUlFRlZTeFlYUEVmWUsrbVJNS2hKZXV5eExHbUljaEZiVFZtSE56?= =?utf-8?B?UXRHV0hmWVQ3bEdCc29STmFDL3BIekhuWU82WFJxOVFvSTFvVVU0bmI2TU9W?= =?utf-8?B?Y28xdEU3ZnVSVXJRazZCdXJSTlh2bS9vQzdRYk1zR1pFelU5TTRkK1FiZG9m?= =?utf-8?B?eTY1VmF4aUxFRTUrTVcyMUhJK1U3VzYza2FrdjdFc1NKRlpUc2Ivb3pEYXd3?= =?utf-8?B?dk9wVmx6OVJSS1ovai9zVm5SRUZvbWJ4UWdqSTllY1pyVG5lbmtxOHlGYzRm?= =?utf-8?B?TEZDajdLZktNN1dNdzBoQ0V0TXEvZFl5Y3paa2ptb3BNcEIxOXRSR3NXZUJp?= =?utf-8?B?alc5NnhHRS83YXIwcG9XRElOb0JXZmpyKy9LWG1MZ0hKLzBOU0FQMXRjRnFG?= =?utf-8?B?QzRvclRkdlBLU0FtNy9wQ1BBc1pYbFQ3VFFzQnZnQW1scU5NSW1aNW1oRGdq?= =?utf-8?B?eUtmZmc5TkJCS3BqYkZ3eGNhaXhid05jY0VmRUdEV00vcUlFMTJKd0ozVTNk?= =?utf-8?B?eDBiS0JadnZaeVhSZHFLS2crWkdScllOU0dSWnJFcWFGSTZtcGxRZ2hqZS9P?= =?utf-8?Q?5B4Yeq9LHHnRQwvIba?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9370dea4-944d-4de2-7e5e-08df2607d931 X-MS-Exchange-CrossTenant-AuthSource: PH7PR12MB5685.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Oct 2026 13:18:46.2580 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: dg8hOsAu34X3cBvy7qzJrLJthyX+dEWT7RTepALjB4th8OQQbYtB3CgackcfcwXE X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ1PR12MB6267 On 10/9/26 14:42, Jason Gunthorpe wrote: > On Mon, Oct 05, 2026 at 08:41:32AM +0200, Karl Mehltretter wrote: >> static inline struct page *sg_page(struct scatterlist *sg) >> { >> #ifdef CONFIG_DEBUG_SG >> BUG_ON(sg_is_chain(sg)); >> #endif >> + sg_dmabuf_cpu_access_check(sg); >> return (struct page *)((sg)->page_link & ~SG_PAGE_LINK_MASK); >> } > > I'm not sure I understand the overall intention here, I get what this > patch does, but no distro could turn this on by default when it > touches *everyone* using scatterlist in a performance sensitive spot, > and anyone doing testing can use the existing option - so what is the > point? Yeah, I was just about to write something similar. Patch #1 in the series is correct, but I would add a warning if SWIOTLB is used since that usually doesn't work either. > I certainly don't like this patch, and I don't like the word "DMABUF" > in the scatterlist at all. If we want to add something it should be a > general mechanism under DEBUG_SG that allows anyone to 'hide' the CPU > list from any future access. As Christoph also noted the fundamental problem with sg_tables is that we stuffed the input and output parameters to the DMA mapping function into one data structure. So by using a sg_table DMA-buf accidentally gave importers access to the physical address as well with all the undesired consequences. I think when anybody wants to address this mess the first thing which needs to be done is to have a container for DMA addresses which is independent of sg_tables. Regards, Christian. > > Jason