From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from MW6PR02CU001.outbound.protection.outlook.com (mail-westus2azon11012049.outbound.protection.outlook.com [52.101.48.49]) (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 9C4E813B293 for ; Fri, 16 Jan 2026 14:33:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.48.49 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768574016; cv=fail; b=ES2bAiclB332mDa0fOmP4YP2UePc6hNss2Kv1Xw3gJV0K72yPJKCBIDm2XdgF5AAgZDnKJGl/MxO+Qb3rNjQUBDY12mRcfQ3LrQLFa22UEFLcliPd0CPVyz7vEYP/rdwQFr37zW5uJfBjQeDLqwqozJQkIstIBwmxH3Vb6FbYxg= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768574016; c=relaxed/simple; bh=n+XevbToOiRKA58mq4itt1XxUyu1DHMC5KD+JJ74kJc=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=ft+WXvMbvNqImJAkuYzPw73AI17mK03kUjCr2Q6zVysYUXc3fgp/sQ/FR2T96+wrfjy7UgvIkKBwjOrNanc6LuitFnOqtgnPkgQ4IE0yzmji+gix0BvIrObw05PT+5Io2D4QstA9Uj/bvdSRZ07DHhT+lk/QtoEsuVtZengFZ1o= 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=FzTV9Y/t; arc=fail smtp.client-ip=52.101.48.49 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="FzTV9Y/t" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=Si4ansVdf9AtGKj6Fv8K2kQPSeOQVi6mH4gE/3Dmck97hFtkJfnzeitWDCWuh0GL4tmoo25P2tYFiaDdsNLf7D6UCpZoyyTVzRaaczC0bP0haIzjucH9+mZcG5dkhtg5mVGYYaDYoXeRxt8Rsyi/FX5DAv504JRSPW/V3Ws9rU6NnkSkOnuaqxXahBc3Ed7a+GEmcUwlBZH+Xp0rkq2ppq7w6snvRM0oxneD2EOpMXPKOJGIXCHzNaK4u05NGJxgMJ2TqVrjUOG2Y0KUfh0MnUmKgbvFDHb+RTvdMggjD3wM0zd/lbv7E67o65fqiteCi5y6KsGeelW4iwBEkesg5g== 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=n+XevbToOiRKA58mq4itt1XxUyu1DHMC5KD+JJ74kJc=; b=LG5APnlfVboLKS+2P9ss5ixgx/HC/akNw2ySPsY8w9t8Z8qG6uZ++IA3zO9Qhq7uj9Ey8nlbZt68XOiajbPqytY8L50r8vw9IOGFTJfxGhr+RxJR1+vpKsQiDfDlO/k+T09UxmOAnK7GOFFiTnH7jue8JdjTMpafTRw7coWvR2X6kLQEZq+xSnMIcCnYCigrwE/x2o+f6iKJQZ3MX98r5CMqzefD+TKq5MDWrSYQm5pGr6Fh+Al9Lk+C1dVto0bstR+PjE8jHvDJZUQdHM7cL34hbD3JiHVPQvuFFncdYio3q1nnNCjd5XIscschAX02Ntmv1wPk/AsIuoUwPQR/5A== 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=n+XevbToOiRKA58mq4itt1XxUyu1DHMC5KD+JJ74kJc=; b=FzTV9Y/t/FXfOn3MsSfylonndBNgxD/Pv6SBbUgipjN7hRGAxgca88YEtWBoLm8C7OZA2z+h6ptAYgOMkkfKSKhqNbsLkVkdEr/SaSjxtIhowQydVnZ5O4IbNXUmaEmt2DLOJ+mCHisoS3wWiJtX4p+npLhsJgNnQ4jRsNUw9bOxi4l/7hEvyrEhiP3cNHHMWv5zTOuvxu7uuzDUaMhhu+XQ7V1xaRpcEHZ+noo8SfhazkBlXV0cgVnsCUowwV6AIPAbIpuWB4JtN2n9UaSAY2eTV62pHRLcmBxTnee7hSedH86BWgAzCcFYgAJWsk9q1OGw+USth9qtSZS599Y/rw== 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 PH7PR12MB7938.namprd12.prod.outlook.com (2603:10b6:510:276::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9520.6; Fri, 16 Jan 2026 14:33:32 +0000 Received: from LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::1b59:c8a2:4c00:8a2c]) by LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::1b59:c8a2:4c00:8a2c%3]) with mapi id 15.20.9520.005; Fri, 16 Jan 2026 14:33:32 +0000 Date: Fri, 16 Jan 2026 10:33:31 -0400 From: Jason Gunthorpe To: "Tian, Kevin" Cc: Baolu Lu , Joerg Roedel , Will Deacon , Robin Murphy , Dmytro Maluka , Samiullah Khawaja , "iommu@lists.linux.dev" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/3] iommu/vt-d: Use 128-bit atomic updates for context entries Message-ID: <20260116143331.GJ961588@nvidia.com> References: <20260113030052.977366-1-baolu.lu@linux.intel.com> <20260113030052.977366-2-baolu.lu@linux.intel.com> <20260115132322.GE961588@nvidia.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: BLAPR03CA0069.namprd03.prod.outlook.com (2603:10b6:208:329::14) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|PH7PR12MB7938:EE_ X-MS-Office365-Filtering-Correlation-Id: 32d8eb5e-c1ab-4479-61ab-08de550c3950 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?ID0RwfbS1cPl/IIUjTqCUmkaFa921kWd9hruQWJodpCIbWAHjNhQkSotnuR2?= =?us-ascii?Q?kqf4IFUEcol+inobh4dQJdG3oIy1jQX9A5PBI2FXKoUoHqfp9i6ONWHc9z57?= =?us-ascii?Q?qZcZwxV2nZQqeaEZPIHnEs7wbnmRFmn6WPcMG8paxIiczMDG74O48cKygwni?= =?us-ascii?Q?79MBLOMIHMiRJ/+SH7rW5UkQ/9gPupp3zxteAMChK8N0qqJZcX7bvBkuU1i4?= =?us-ascii?Q?ukJnJdj1OlHE4w50CkvxE6s9kdqb+aXpPrIoIgDETQ5Oe9IV2R3KQOv5EOFC?= =?us-ascii?Q?DCGaqGkZCP4IyxmeEDFX81Yrt6eWKKL315i+qFG0NG+vrxUIM+huzKnHzL3b?= =?us-ascii?Q?cjAEGRF0Cmd0TgAiFWNBTOgTH01HvS9X3HnGj1uALQYrOlaJdbafyGdg1PDG?= =?us-ascii?Q?zUm13rlpXFASz2WMM3nhexdtPD0yXFHc9kfuPQSEzFYrP8vnOjBbSG8RIDJb?= =?us-ascii?Q?snKo4wWWQkGSTHJEVIkobisNVTwamjgmEROvkMpb3/5SYCWgWPLeo6vgYYcw?= =?us-ascii?Q?Ch8PncNjRX5v1VZ0fQJu2VUggn4wz/M5lBwXDq3wnwxWwuWR8sOldH+WF0+Z?= =?us-ascii?Q?GVea26Gu93Hx8o3F8OGSTsuAARK1225dUQ0+cxRUDD2hLG9pVs5wKqTfWarn?= =?us-ascii?Q?BtbHjiwaOhVx51U2UmL6PC4l+XOiRoy7hIWIsR2JB+vybnygN4eTuaxuD5uq?= =?us-ascii?Q?JOoNwPE64WLaA1PmixxPSzbWFxa/ua0aAXc98uDu2Z+9XYElJFXOrVibbQ3w?= =?us-ascii?Q?y9oI2rbl4tRYOqC3b9MoJopOWWviIYjKhv9IbE2YpiBc9zkZMHfIuGXqmhiJ?= =?us-ascii?Q?IBSAZ/pbNU6cTTSBvJ5o4vfs6ZEcK4ni4JRhAyFGEAHfwZvQUGCN3I5Uj7Ko?= =?us-ascii?Q?oPlPooZ9SPuynFImyaqE6zKB07V3Lw9rqgIAaJIYSP7P1dEJlDh+sv8P6lWl?= =?us-ascii?Q?IlvHAi7djUT8qtXtLUqBWWfhe0psjTiv9+zSrMjA4k8fVmGi19eWeS+a6DEG?= =?us-ascii?Q?4nfQ/q+ws8ZE7Iau8dEICqOh/DntYVkZ3wTlG2QobOJzX64AYI1pD7qwAU2E?= =?us-ascii?Q?GkC8DM7Uo+d7ee5ivv3X1+4jSCjfgm+2hszFzX0+MATm9fi/YUGl/JP+zKND?= =?us-ascii?Q?qn7hTzEaxvd9Sw0HGeoo3zzOHoX3dc0sY9u2z8YkODSFlJDdCv+9CheGK7In?= =?us-ascii?Q?KOzK5+4/U6eW7yHtsAfTnmKOivwjM/YDtlUBITvkGScipQFgan39T/RDg8fq?= =?us-ascii?Q?HBm03GP0e4bVe50XGsNm+DNzsIVafdeYy5y3N6gwHO4RLNGd/Sanu+O9C2D2?= =?us-ascii?Q?PWZlZxOMsircgjOv2irIDL1LuWUw4jb7Ldsf+zN6f/1q08sqI1cpxeHfNw48?= =?us-ascii?Q?+PNIRfEIAB9ZLrtd5hySKfdk99mEfsPVYpQ1FZTbDfYkHNUbakpibo9VSJz2?= =?us-ascii?Q?nOs1yLnkv7nG/1xVi0aWSzKNopQK7CpnBvPAS4dbSBaHSjQVoYeshcSPlHzP?= =?us-ascii?Q?r3VAo3GJJn8frNSvqnjcfJVD5NEWordtBrhb0zd/lll76zsE1oXymXLcwkzE?= =?us-ascii?Q?Y8zezOdXVJaO/k2HaZw=3D?= 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)(366016)(376014)(1800799024);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?KOhGUZn8jJBpiJOZTqDrmrry5tPoyvvnSYIFRVaUXz+p08b9I7oIvwOumRza?= =?us-ascii?Q?LAHUVKDK/0VsDAdwRJdafKJcju+M5HUBi4ikpivUJslo5qz01uzWwbMhz5St?= =?us-ascii?Q?j1Q6gaXSaYBE6t4jMXHQrCL3DniWD6zg8GoFz6bulfTtZysmGZc9qqh0LQed?= =?us-ascii?Q?NCBb765vuBHf+zQky4wH423k45Wk+GKIq1CaXG8kjy7Lf1ugJWmTaep+my9g?= =?us-ascii?Q?ZNmXxtRMtOR4sPVWfCVGX9/MkMeUCqfNnvFjK/xPbG+AoRj84+Dj7DT7FKwd?= =?us-ascii?Q?/VT7ctffXZgfjeAk1IrdxxXBNkcsoo5PZLcFCwooZu928F6RYpgIJEedEfKR?= =?us-ascii?Q?HA/d5jf/NsKIeDPv8JTGcIIvo1GWqQk3kT11m9EntPLs+jbfKLCYzfNJd93M?= =?us-ascii?Q?RrphvSyYY+Q0qnDYLWny6als617MggLZcI/6QYHm98hwxVUrkZJhRV/EywZQ?= =?us-ascii?Q?YlN3w97hp/iyZMQ01Lwgf/QzwBPgoy2SbJ84LTB5rvFlpHg0/G2hmkcpiZWD?= =?us-ascii?Q?EUQNKNsTfldZPgzPMJb2RTeZh76eguJZx+LvmtliZaOQlZVWdaHsWTHSQ3T2?= =?us-ascii?Q?DMom5Lg7y75grtqzJlzMJ70/PvhEyqITHsVtPvP9WSdq2ldBgDMMYdZUSnDT?= =?us-ascii?Q?Kjt7sc1t46XapPnKegVbMnsQwWI1aQyljAUnUEW2SpnJAe2kq6IglkCU2yQY?= =?us-ascii?Q?yvq0ODpJZUsNFukTCB08oDxhgcjeVBPgyMp2yEiRSPMNPBPWC0HSDpDoXZXF?= =?us-ascii?Q?fH4yhoF5KoKqNpO8RJPx8osAeUQ1pAE92mW+uAHH7yK2F5qxVfrRVAfbPrlg?= =?us-ascii?Q?ZddvndsL8pzTNBz4g8x6EwWeHaEfeZ2j9OCOAuihJh5G5aUVv/6FvabEfGU7?= =?us-ascii?Q?ODyLKmNSBA02+E3lsjej/ltM5ZXD56roXsv9w9CzJFCkjvDbpuRqRxmftJmP?= =?us-ascii?Q?OAyBpN/I7bPot6+ASEjlH52zJIJ2yXTZYS+W3E1rSl5dgXr135gVNc9XeGfM?= =?us-ascii?Q?qI3s2rJjTPN1e8xcWVE04AgmIoXF+eurmJ9YzGG3NSPoq9XrQKw8QXzCd/qU?= =?us-ascii?Q?kXAeGQOagpz7k3aaUQBul4T8KCD91QPavh4F41HLic4PoPkQsARO5luU0NRt?= =?us-ascii?Q?8sAD2QL2UmlMKrIIWCSjbXnbDPq1kjODbkyGLS5fmuVgwTOmuVmLrWoV+Xxy?= =?us-ascii?Q?UKVZkFq5h2Thxc0oYxqqrVh01hlS/zO8ppQ8qmh9N/mfYuN7z/vwZcynRwqa?= =?us-ascii?Q?ppIUau00iVEmNBQMRScUpFCEeCR+UUhnUA9Br0xJ4LLl5vA9zDlveXusfi5E?= =?us-ascii?Q?VaTZxcH12VwWi0B7wXrL3feY3Zwxa4Nspxx1jTnYIgA9nNmcd6JjcRpXAOIg?= =?us-ascii?Q?ierXJxkPucOvhjgSvs2mjB/6yWww+oVIxiWxaGxFKEgBhtbyH3qcSVngKTe5?= =?us-ascii?Q?0EYT+ZBAaFnSsTUGZic4BVBQubnabLJIqARHLgI9nIdLwNCHfh3nTDMxJKz7?= =?us-ascii?Q?1b1cU0THKVhu1bdpnskqhVvqLlrVWGwOS70agjsUInNHilxU8XurojbFRvFP?= =?us-ascii?Q?q9oR9epz+nraaQKNNegUVlhRnuT3MILRpnKyQ+Q+MqORVP3M0P6LJT1Zk2/W?= =?us-ascii?Q?JEHgjmGHnYpm+86mhpm2/YE/ws34FXcOKF64qvE89mzdPE1ph3sAPddZ3twD?= =?us-ascii?Q?NHclr39sVm8gna9UNWrfPAkJjU/bt6Q6YPhVpkPg2GHMg10ZpzZDH1vGo7+9?= =?us-ascii?Q?YWc8kMwjnQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 32d8eb5e-c1ab-4479-61ab-08de550c3950 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Jan 2026 14:33:32.4172 (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: QmP1G4OJHz+LKIBfwvDNkK4TOEVMQkKAOTMEil1RZvLN59YiMMlSmQxBafQ+iPao X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7938 On Fri, Jan 16, 2026 at 05:19:52AM +0000, Tian, Kevin wrote: > btw the way that VT-d spec describes it as "software MUST use > 128bit..." highly suggest that it's either as AMD or with exception > only on very early generations. Another exception is VM which > may have hardware supporting 128bit but vcpu model doesn't, > but I doubt it's a meaningful configuration nowadays... The VMs is an interesting point.. I think with a bit of fiddling the entry_set mechanism could fall back to 64 bit operation automatically, and that would handle the compatability needs. It would be much less hitless in such systems but who cares? Jason