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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C6512C5B56A for ; Tue, 11 Aug 2026 19:30:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:MIME-Version:In-Reply-To: Content-Type:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=OsAxR/wBCb92UrIdfygCWWHNE8eP3Fi9GSwHviDiZ2o=; b=TfPoLgxnE8qakO/DkXXDjnUbEQ oAV0iccqgbYtcDJiqinfaXTHUsMptFEEfkwvVBi5L2uN0zP0l54GouGB1PH7U+ulxu3eIQKcfqnCq Ks48K4sI1F2q5MsLYs9DMAf0rZLAmxoZiNg6cv34nShAnG+Zqj6i/TqeaTAbm2hxyECPo5LXoyqWx DhqfRniYbbEHk5W/XDomeNj7/hKW5II9CXRVSlkxAP8aG6cEcrqZusfZEPaQaroP7N5hHGlpAW5E1 CBj3e6x9+nfBQT0QHVUgulJtuDUE445KdaX0+uu5kuLbWO/7QUg5dAbM+4YJpaDhj97Rb0ktUY7gm jFAR7+iA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wtsBM-0000000EqEC-23mr; Tue, 11 Aug 2026 19:30:40 +0000 Received: from mail-westus3azlp170120001.outbound.protection.outlook.com ([2a01:111:f403:c107::1] helo=PH8PR06CU001.outbound.protection.outlook.com) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wtsBK-0000000EqDW-0Gty; Tue, 11 Aug 2026 19:30:39 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=pwNcpRC0uw8lWfJWpF2+YEJn6+rl5kac/zWY2Abp+jK4yRJwQHM+05ELeLnIdxzl756a8WzADducLQ+qMxpmHivZxPNghOCtDypQIB3rIj0RofZCGNwE2CaZX85pwzAP03heiy6vKfB0lm4vQ8SaJPZdU4bUmwZ/4fuDewwFnejvh5HkxxwNhlKzf7B1K2udYL506645i4TPNP3E7zeO7yPeabBhAEPNTCDTG3xN2GiK/PsY+QHIBBj0iYrhmFIiCY8c7sT7mi3wa5Qc9NAAR2WL6r9/+HNeVfyAA7y+9mjhHRueF5MbKRAbsJ2ZXcIcCrbfs973EK99aikTk9EQPw== 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=OsAxR/wBCb92UrIdfygCWWHNE8eP3Fi9GSwHviDiZ2o=; b=LSWCznSDrpuwM1aQuJIQmBvrDPTMjo8ekC25zPdBIIHCODCx7T0VpVaknRvlR29pWG6rSiHr3pH6w9NbdoPuH/JBC8owkSQiCV8MVjTC9+usgjlbepLqLeEM957rQIb0SPNQFL5U59MBYgIKWfmyFah82Sc+DevjVDrwVAgUHznwL8Qm3px4lbOxXf40NNj2lrabW7cueoAjvtnrPgx50xK8kdSrAVWb/OGFlpn5Rqwr1/0bM4+beNiPTzAThc8JADBGoZ63draFBHr6dTW4sPs4ZEMfcTf2Q7Rxr3DEr6p8Uy3jyUoZ7cFHvj6ZA6V5t7l7hn1pZvTUYFXTP9rO0A== 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=OsAxR/wBCb92UrIdfygCWWHNE8eP3Fi9GSwHviDiZ2o=; b=pENBEZZjmQzI9PFooQDdHD466OTOYv9P4R+BcOkWbQBuscB0buSonYE8c9b6YCLm0Etm2DVbO+QCi6/4E3pY4fe3Pt4MIdZuXE8qKMiGERk5WUpQsYMID7ErH1VnAwviMpkN0puzO4ZKuVM/nO47b3qT0MoZx2LYybCInFiDa7vG1hjYq54FsixV3dX98QDj76i1Fx3A2WdlEtV7XIB9DR/I2NKuyGs+VKsq+kjZ3qUwewLuhi391+qTWviZwb9XTczKFuehyyo6Vj29YXqPq3iDDz7Guipq2ZiFIhIQJn/aSCSZ4UC72GZOCbprHgb4lZ183iyiHFySxLVk7B7UNg== 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 IA5PR12MB999277.namprd12.prod.outlook.com (2603:10b6:208:608::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.292.25; Tue, 11 Aug 2026 19:30:32 +0000 Received: from LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528]) by LV8PR12MB9620.namprd12.prod.outlook.com ([fe80::299d:f5e0:3550:1528%4]) with mapi id 15.21.0315.011; Tue, 11 Aug 2026 19:30:32 +0000 Date: Tue, 11 Aug 2026 16:30:31 -0300 From: Jason Gunthorpe To: tarunsahu@google.com Cc: Pasha Tatashin , Pratyush Yadav , Mike Rapoport , will@kernel.org, changyuanl@google.com, Alexander Graf , mark.rutland@arm.com, linux-arm-kernel@lists.infradead.org, kexec@lists.infradead.org Subject: Re: QNS: ARM64: Cache coherency while doing Kexec for KHO Message-ID: <20260811193031.GA638489@nvidia.com> References: <9huzldaczcr4.fsf@tarunix.c.googlers.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9huzldaczcr4.fsf@tarunix.c.googlers.com> X-ClientProxiedBy: YT4P288CA0006.CANP288.PROD.OUTLOOK.COM (2603:10b6:b01:d4::12) To LV8PR12MB9620.namprd12.prod.outlook.com (2603:10b6:408:2a1::19) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: LV8PR12MB9620:EE_|IA5PR12MB999277:EE_ X-MS-Office365-Filtering-Correlation-Id: 2136d4b9-056f-4ac2-fdfd-08def7df0243 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|23010399003|376014|366016|7416014|56012099006|11063799006|10067099003|18002099003|22082099003; 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)(23010399003)(376014)(366016)(7416014)(56012099006)(11063799006)(10067099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?l6qhV7HOhUm3rz3vjkg0JXw42Airx7nAiOf/0aVu8bvVLJV2G4aarrKtapvT?= =?us-ascii?Q?I9n+6pp11JsuOwaqwGDggjZdWEb8ZjLCVD3XF5d2mDG+srpxkGnrW/qzCuZM?= =?us-ascii?Q?QfqaVP7V5zPeUwUPfaFirp+zsQsKaASwsG50VPXFOrWSppVdcx+DHjgv6xxF?= =?us-ascii?Q?tWobfB65jTDGxh19qN/RM/OSL8/Nbvmh4ZLOkwPAn/LIjhImhuAWKjrMFZiO?= =?us-ascii?Q?nj0Oys5V8YyaNnHIJr5rS1CNhgoiUD/3XJ4S/Mc96RQSzmyBb4DyVJLpLgF4?= =?us-ascii?Q?8Uua0ka3HWZeG0yKl3chhQPGu/ygYO42e/aHGfCUTmMFWCoyg2mNx1NExcrI?= =?us-ascii?Q?EsR1oz0FVU3cmUt3QgBVb6zdq5v3i3yszBFs9YUKa1v0EXOnyco0zUVlacTY?= =?us-ascii?Q?wkAsIJXgWFBQ5DzYzm1zbymEVQ00pkrWFlRuyNWAKda2IRLfjlmC8S3F05fJ?= =?us-ascii?Q?UzheJjVXbgsHKeGzim43Wq2AC57f/9HzuyzaCvMdpy6QUy32+M2QlzTa1L4z?= =?us-ascii?Q?f7S6YRcLcsSG4xHZCry47UxTtsi2t4pJqFS+3X0+XKobp80EiBXqymjd+hqi?= =?us-ascii?Q?glhDgxT7lF2HJFT8/qrJ7INWD+5F+S25Nfk1YcrDZe2R81Ie2+PLORPRAuC5?= =?us-ascii?Q?axf8yV5/VsJYaj4K21R8BPPlRNMn/K8LuI3SPrW1B9t95ims4KJu4CVodxWv?= =?us-ascii?Q?pwil4XZy3e/jKUoS7b7xDjnMRMXVAAYFoXMZAkniRAlaDWimnUk8TintR4Yl?= =?us-ascii?Q?ukOqNCobLdVupCLA2gPCK5RuKT/dCJeToGGrKUmT90VnY45sdH0qAD1IGXfg?= =?us-ascii?Q?YPfIb/PW9Qclw74ayAz27Ld4iO9enEttyMEZnzLrG5LUfLl1Vcdi6mTmlimj?= =?us-ascii?Q?zUAgenR17FRwEF6WqL2soB8qzCgKVAAJXmmLmniDV80LnGfXhyRVPYO6ON+q?= =?us-ascii?Q?cAVxHT227gE+lSe0HjLiBROoZiS1OLZhb72iJqekc9foCQEkMzp3RxfylgFe?= =?us-ascii?Q?v7cUm/FJfmw+J2C3fOr1Bsl9gQH6G++L5N4JygiXDfKF/H7pwWbc4ZjlFXYt?= =?us-ascii?Q?pZx587/FtYE2gq2fKK9ImkBkfAFWiLj/DiDZ0GQdoGWepdhgcApywums45Bw?= =?us-ascii?Q?aPnCQxsKLCCWB6EZ2moR7YFZ782XNAISgVOFTAYXGCfTlNeueruSeibAoS3A?= =?us-ascii?Q?lZ3LA1RhKzrgTp3YDXJrr50V59dSAVywWEwSQ0zoLI5EDN0AOXSs+RHpJ1x7?= =?us-ascii?Q?XxFVDM4MpAqQMNvGjv1SHZ7nxtzHMP+uGFA8Mt0J2Q5tGG26/4a0K9iUdSxp?= =?us-ascii?Q?FAAVkJpRbXRJXmKSt6SOXjBrDFqGR+H+ESD0osBL0nLg9pvBl4U7suGhfO8e?= =?us-ascii?Q?ZGRTiVU/X8WNgAFwKw2t+5vUomFAQx0Rw7VbNIEhFJX926m4FWeXnvqEGbAt?= =?us-ascii?Q?Jf5ySYXE26Tj+/4BAivnHYSNy0x9EjDlZ38pa+9pDRD2PTDiiB7NPwHHqHkT?= =?us-ascii?Q?pxjsOF9JyMCailo+E8NMiHmnPHrzhYclGj4A3R0zpBAabThiOh57Xv/9S/7I?= =?us-ascii?Q?GBlCF9IgR6gVNwy95rSXZnMcsTVVOfkwd4RQGIknW6j8aqEiMv/6Kneylosh?= =?us-ascii?Q?SFy+ZP4UhGwmZP5+4fkcTIeeChTNpc6PBrj4CK7iui431D3HcXldDVDfdx83?= =?us-ascii?Q?6awPRASySLHu/kCSIJ8de5uChCmYnYaTVX8vT7OpKwNjgqh3PYQ3ugDIMFqZ?= =?us-ascii?Q?9gx74ttqSA=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2136d4b9-056f-4ac2-fdfd-08def7df0243 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Aug 2026 19:30:32.3039 (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: 1BCSrmo6O9G0Si9ax2f+64vuJFm18BCP9KeXlCo8LlO8ESf8ylg1bAazmevDQLXI X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA5PR12MB999277 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260811_123038_109316_7241B922 X-CRM114-Status: GOOD ( 16.94 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Aug 11, 2026 at 07:19:11PM +0000, tarunsahu@google.com wrote: > > Hi, > > I have a question regarding cache maintenance for Kernel Handover (KHO) > preserved memory across kexec reboots on arm64. > > During kexec, all other CPUs gets hot-unplugged where they flush all > of their caches so there will be no issues with any KHO data preserved > having caches on these CPUs. > > But CPU0 still has not been flushed its D-cache (Is this correct?) and > it will only do flushing for specific area by kexec_segment_flush(). > > So for KHO preserved memory, if its caches still marked dirty on CPU0 > they will not be flushed? > > Is my understanding correct? or AM I missing something? > Also if this true, This will be a problem? > > PS: Pardon my less knowledge on ARM64 cache coherency. Yes, I think what you outline is correct, but I don't think it is a problem. As long as the CPU cache implementation is physically tagged and everything kexec runs during boot with paging and caching disabled is flushed it should be fine. Once the new kernel comes up and installs a page table with cachable attributes everything will still be consistent from the CPU's perspective. Anything in the new kernel that needs forced coherence, like DMA, will be doing flushes anyhow. Jason