From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) (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 0F7181482F2; Thu, 30 Oct 2025 19:39:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=205.220.165.32 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761853154; cv=fail; b=XDqJ8gYIMchgNMao74eAqb2/rk3ibsxA8sHSAeCwBaubumxqrYrWaGgplhe9wE+J5yOBq/yDM/CJa6V6ei7vmUIX2KCuWeyNs1ta9WJ4TLSnFtnX6YjCMy6m8/pdj61rxdLVbBROtqJ3ECS7jNZO1cqxxE0Zir0QChL9UkPUK8Q= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761853154; c=relaxed/simple; bh=Ji6HzeYRD24Fj3TNkBTOQbbe4zU7xIsTulkYePhstsk=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=UG++7JlpJqbkP8t6Cyzq6xPQ+tfIo0pOy+FBZKD7O12dG3MSIBCuWL523oL/vna/zBmd7hVcFwNytm/1qG4bVThN6h4l2U3uD2P2TWddHAqSe71BRg8VGylq7wateRF5FTsFUyo02w8/rd52LSn9OL/TM1tLFZ5NCWje79ijFjY= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com; spf=pass smtp.mailfrom=oracle.com; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b=qbYRMz3a; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b=F54Yn4NL; arc=fail smtp.client-ip=205.220.165.32 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=oracle.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=oracle.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="qbYRMz3a"; dkim=pass (1024-bit key) header.d=oracle.onmicrosoft.com header.i=@oracle.onmicrosoft.com header.b="F54Yn4NL" Received: from pps.filterd (m0333521.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.18.1.2/8.18.1.2) with ESMTP id 59UIK1ml025280; Thu, 30 Oct 2025 19:38:21 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=cc :content-type:date:from:in-reply-to:message-id:mime-version :references:subject:to; s=corp-2025-04-25; bh=Ji6HzeYRD24Fj3TNkB TOQbbe4zU7xIsTulkYePhstsk=; b=qbYRMz3atOu16KHKYgmifBdAlgencn8M1E Qm7sCUiwGd+JlR9M4HJFTBw5mPGBVNCDXhD13tZtYv3gFKKxw9uVjMDjf1Q/bAt/ Sv/EU6VDjKdwxzXAvi5OAizCr5HgJnnkJmtGSDad/0hkHBTbpOEREwRKWay0x21I z/q0KnRFu5P2szGpOJhxuQHku0Re9R40W8wEigepxfiwhr6KUHXhg7eelKemy1fw MnmEgI1Az2T0kE1FGiy0k7Kcof6fcUFkCmAVrdN7NyU9tf7jYj0gp9xkc3Bzob7x q4rf8EDSrwcRtCgcrHkmwva09rB0SgY6awubpwvci8GnJy1rqaMg== Received: from iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta01.appoci.oracle.com [130.35.100.223]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 4a4d6q069u-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 Oct 2025 19:38:21 +0000 (GMT) Received: from pps.filterd (iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (8.18.1.2/8.18.1.2) with ESMTP id 59UIE6jR007817; Thu, 30 Oct 2025 19:38:20 GMT Received: from ch4pr04cu002.outbound.protection.outlook.com (mail-northcentralusazon11013044.outbound.protection.outlook.com [40.107.201.44]) by iadpaimrmta01.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 4a359vrpjh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 30 Oct 2025 19:38:20 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=bDoh3sU0LSMQB+PwPxYw2BJMbT/aqGU8olhoTb611+jYZWpAa+YOTv/AbhYG0FjjbTtjxH71FHg0qI8EuvV7RK0ns8TnLqipzv+Epakolxn8+Fnk6tIYrUpMunraph0KQ43NU+4LJsPeFoOcWN0Ar9rKeqJyBTGhy9gzNtPPlI94J0Ciy/XhHqpYuRXhOwhifa06sa1e0QpPY+Nphw+nyFtsqVrPLIbEobPCrknMz/D2sgbxjxEM7f4Qhf1MzAAf+SnHTryY3AzRQOC3l58ncOdlr8XW75aZRQYfsuK8Il3EsPgTZhKzHhofsnO9l+vqJp9pW5c4MNmYeH97sioXyA== 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=Ji6HzeYRD24Fj3TNkBTOQbbe4zU7xIsTulkYePhstsk=; b=KQ80QQkRtBRhfcm1qlap2DdvlbAVo77tXynTOgOC02zRP12+pzUguM7PmJ2z5o80JrohjZL/wrGgW0M/t3wOI3G3HeLDd7Mn9AEHfqcYJWjMJ+SfuhQK9c0lPZ0YtEAgjNp1aL+XBbHrw7aNMnaXHWUPfI3ckoB8hxjMrsO5yeRU+3eUKsBO93bjJ/q0D5363zxgA5THDE7dkBfKKRprMY3cJIR91DkTQsWA98i2bI6wKca5Gb7qRuxqLhQTH/9jIZ6t90Yi/VSyCq301LmC3O449OCSINqaJOtJNyIEs5ejsEjM6c+DGEm5I8Ek7yxTXB5a9OqdB3PtPXJPj67t1Q== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Ji6HzeYRD24Fj3TNkBTOQbbe4zU7xIsTulkYePhstsk=; b=F54Yn4NLSAn8jIj40SVv4dGx7vPKozf/QDGypZDDMvL2HhvLWykmyboqQ9Kyb16r/4CgW2Kv5nmA+ZFhonIcYPnXpdAOoOveHuFTL4qJiYSVc4N3ekzw/RI4xP7YieLZYfsX1avqJGSm0UYsEydTLZZwz1LDzE0pzPI7vmc+WJg= Received: from DM4PR10MB8218.namprd10.prod.outlook.com (2603:10b6:8:1cc::16) by CY8PR10MB6852.namprd10.prod.outlook.com (2603:10b6:930:84::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9275.13; Thu, 30 Oct 2025 19:37:58 +0000 Received: from DM4PR10MB8218.namprd10.prod.outlook.com ([fe80::2650:55cf:2816:5f2]) by DM4PR10MB8218.namprd10.prod.outlook.com ([fe80::2650:55cf:2816:5f2%2]) with mapi id 15.20.9253.018; Thu, 30 Oct 2025 19:37:57 +0000 Date: Thu, 30 Oct 2025 19:37:55 +0000 From: Lorenzo Stoakes To: Vlastimil Babka Cc: Pedro Falcato , Andrew Morton , Jonathan Corbet , David Hildenbrand , "Liam R . Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jann Horn , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrei Vagin , Barry Song <21cnbao@gmail.com> Subject: Re: [PATCH 1/3] mm: introduce VM_MAYBE_GUARD and make visible for guard regions Message-ID: <8f4ad5bf-cd5a-4b93-8332-bc8b306d0e77@lucifer.local> References: <7de40603015dee82970f5d37332a6d5af7532063.1761756437.git.lorenzo.stoakes@oracle.com> <61ae955e-310d-488e-b350-59bb809f06e1@lucifer.local> <053f3a04-9195-4f8d-8959-42e0c3ba077b@lucifer.local> <72ee2324-d599-44b6-92ce-ed0afafed78f@suse.cz> <6334993b-ead7-472f-bb82-bb7d6f15f3ef@lucifer.local> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6334993b-ead7-472f-bb82-bb7d6f15f3ef@lucifer.local> X-ClientProxiedBy: LO4P123CA0553.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:33b::7) To DM4PR10MB8218.namprd10.prod.outlook.com (2603:10b6:8:1cc::16) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR10MB8218:EE_|CY8PR10MB6852:EE_ X-MS-Office365-Filtering-Correlation-Id: e011c7ed-3ba1-490b-dc0d-08de17ebd427 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?8HSUxw7Hudeg4UwgWZliF0IlcggVyLdb57nyAUDnsoq9ePFlrgdf0Dd6w/wC?= =?us-ascii?Q?lextZsIex0TyrfsQObmPSrR8viM8HFa7P25TMlM1uUd0ygznEkdmjL/G5voJ?= =?us-ascii?Q?jowLwowlA6p/hfPWO1XWcE9cZ7v2sBNK01HNULBdA4754iJJHiV4dx/iaW85?= =?us-ascii?Q?7N26HUwNLS6Jf3VjAhD4rv/OYFPOmy5GwVEYcczy+S8fVaVZhLgNF48boN8g?= =?us-ascii?Q?pmclv+RTl5j2ccvSDmcuOhBswhyaXpqSszsZW8j139imbEj81RKVC1LSPdgK?= =?us-ascii?Q?N+yyIzRym+H9xVyNPsCFUc/RQgjpNE8aJxagJaKqpmmLXpY+5mAKSbOg8+pp?= =?us-ascii?Q?B76l4OnttdfVtJLevSYfWxMzqBcA+2+hmWWM1KzZ4rx9s+awNWE/g3rW7m9s?= =?us-ascii?Q?1xnQR25/G0jwxaw0Djw7uoIfJqsrqr/dmoR1drGK8iEe1suOa/PfDMaYmwE8?= =?us-ascii?Q?eziroU3tS9WdhOYSQSwl9S9/KWHfwVeDZchnzbqc6MxMVZtjBQDL/XSjDslN?= =?us-ascii?Q?3wR9t9zya3MvXzVX2xrYOeuIPA5p/fQZjMWhPnO8/5LMz1OUfWNn7kXl9f8o?= =?us-ascii?Q?fDfn+RH/dn6brombE0VqSnxQjvHC9wPh9R8XV7n/VhG4xm4epPNUUtYtqy46?= =?us-ascii?Q?zDdZwLl1T72zJaOynOnNaoFqgbVWfJllipnEANxv05nLU3RKnx26a3FdT1ym?= =?us-ascii?Q?zpyPjopzar+PozznBBZH8mPHYU04e5jh/sz3JzO5uB8rY0X7UrC9+ErVJROG?= =?us-ascii?Q?1phch8EM5Fw0Ok5WpBNzpFk8OIZ3XWE25gYH3SdTBJmQcVUb0p3vXY8Eoi3Q?= =?us-ascii?Q?1wmJLhmdlOR3Uz3ikNkAyCLpxv9dd7aE0/0Fa9/l68mpvcnNiVYrFANnk1R8?= =?us-ascii?Q?9gj4VvdOHUW5qI4+Sz0OgIgKAxH+6KRz8EsXXBca2xddSGXUTe48Uj0HW/Z6?= =?us-ascii?Q?nbgwlYpBdUR1hOt58WuW8MIkx0nVDcMI57e/uL2C8wZHdZWNqJUo4WS+jPot?= =?us-ascii?Q?SmjAB+G39RgeE5/Pi8mPfT6bqjsIQaw4uB03iDIDHWP6r1DtXTDgh5yS9AtJ?= =?us-ascii?Q?jThZm6hWFtraHaYx1mPQsyg81JQAtmsl4aCCSq+8i8RO8AgcUaXRXRs0DeMw?= =?us-ascii?Q?dgN1g/NahE2ARFufWR4rpWcquIiaKZHptJgGXcRWFu5MxQ2roPS3h0W3HyZN?= =?us-ascii?Q?Z2XUcex+8hfWCfXGCDD6GSf+qbs4pSnPQG1kMM2gm5byW+0ZGNouALHB7/k9?= =?us-ascii?Q?/NlZsd2Nl3vPFpecvpexxod+1Tdg199vLm9eOk7WveIr4OEXQH3obzwqjJ3q?= =?us-ascii?Q?aIkXhMdtgccRgHZaNdPKeF/zN58exzg65KvVUja2l28GMIgPOVCLNqupBDX4?= =?us-ascii?Q?fw8cKmCXNlDi0YPFCxvKVv8LPG1Ei9JFm1Eyd/zpyzsXvSVQmiBr5nKNcsLk?= =?us-ascii?Q?k7Nfv/9a/kmKTRH5q3AlppQskt3+8cZk?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM4PR10MB8218.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(7416014)(376014)(1800799024)(366016);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?IRslQZNQe+LCG0GJgBjV4h4nSTcAxdDhiFLdfimmulHOCchOd0LpY5T9suDO?= =?us-ascii?Q?zJa6R+uvVtp0VwKYLfrWYcCNjZ9BsQk3rJP5Wjaqzf3QKlwGRZSnPWzf9q1n?= =?us-ascii?Q?KAySgTlpnRfgFTKGv+rMNwTh4i8Eph7R3lIjadWh61pJC8+2CAhtR76SUskD?= =?us-ascii?Q?b4E8bFkM/qMpxbKqTAX66quHv1ioYMdAoLv3RHAOKk4wILo1TmmjBjTfifXy?= =?us-ascii?Q?UygVc5y4FNA9R64/UptfXHMo4LLe6izFlZKP73EFZv+pZ9H5S2yDVs39gKAp?= =?us-ascii?Q?YWMag/JE6LEOeiyrw5ae8RqMJuQDHLoDsW+eNP8Rfw5NXQ2StRpZAiqYby6/?= =?us-ascii?Q?KuzY3HV3XwmtwzCGpB+ZErooSPF5hHtjXAK+QkImLvduswAzqsZBM1Pe+3fT?= =?us-ascii?Q?SzeUY4qbzukIMOCsNB6zXFXF/EI1NrU1aDYiEXg9MllU2BUynx4blLGgOvFo?= =?us-ascii?Q?dXdy4Cf7oSoyEwx8kkEsN8oS4vrH12pgvt6z8a2TRDRoAnPVGhcAt0C6RzpS?= =?us-ascii?Q?kJ5OtiZRdPoLDogHCrFnyvDjkOeY2bEtQ/46KtwfR3fT0Mbtvym1fmV7q+L3?= =?us-ascii?Q?qc70D0ORDGy54TlZhoXhkoVOh0gi/iTTEd7Zqc9cPVXGemQB56D6S08dG0FN?= =?us-ascii?Q?6/T1x6iXjE+RdeWGEUDXcoGxA2hsPjcHlHv6y2ec8PQu3TD3QOIySDucKbm3?= =?us-ascii?Q?r4FhDte4PZhSpDyBzc1yiq//7fTTNRh0OclF6eudiLVJcmg/Wnd/YgP0gQcH?= =?us-ascii?Q?+2QJzghkCWvc9jK6YKVSvllOUPQu7rt4ISzHRGdn608gNtWlPW0Tg9H60c7Z?= =?us-ascii?Q?Yv+tChFoyE/leEm0thQn9YVSFh2mgsf9L5FHHWAG0vEh3DmFjbRU6uL8/ORe?= =?us-ascii?Q?gqKY4sSa2zSqAeep++o3+C+l/7zrtc/1u2l5PH0/cqkvK/CSV3O59y4hT98T?= =?us-ascii?Q?B7ypPAlVCCRJmJxQmK44WPCU6v2AGsvJNuUyk5mLVdR4UsFTW3wPSCLFMl6A?= =?us-ascii?Q?ObSsfdK8OJ3d+XpQpGqj883Eci7IVYsL+uAhAV7kcr5rhWzNLk9xTC4zwDF9?= =?us-ascii?Q?f6qw2EKtPohXYE8Touea9ZzqjDrdUGRVj+FR0o2jenE79K8Bp9X+Q8NHze3R?= =?us-ascii?Q?0FH3025b3ZvA8CxyA9c1MWxIoA2k2DHfvyoDv/f2Sm0KbA9LO2m/oMDJFK+Y?= =?us-ascii?Q?FY2U1PewYrvAcgEbmmuAOGRBK2IQXAys7LOG4c4t9um+KHuthaFSyCO00LOW?= =?us-ascii?Q?1vmit8B8gGrN6/qscXLVV2SltIoc98TkUwQs2um3fn31N8xEBrNUFXC/f9Of?= =?us-ascii?Q?RnbIOlfl0RHulWChgp2X1JBg+h5BByMUaF49DRVvC02hdtDxgoMUZ73kTodD?= =?us-ascii?Q?dyGcKqroMPutndPn8SKpJwDt6OyO+giOCUs6OnJ1yDPu+wmnTJuctXsUsfRZ?= =?us-ascii?Q?lOz08yxNFfjL0cI/DcKrkRCB8Qla1mFkIns92y1waqOWzyHXnTYhH+P10UWB?= =?us-ascii?Q?XrLxW+xzYjbUpPmNPuTHw2pZsxItnWVLexIWEWCokpndFp2T31ftxObHVtew?= =?us-ascii?Q?qIGs17Du/lYM4VQAK6nNa3q2YqkgZu26/S0jRWXHcx2SxLvFnoscN4lVqR2I?= =?us-ascii?Q?IA=3D=3D?= X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 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 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: e011c7ed-3ba1-490b-dc0d-08de17ebd427 X-MS-Exchange-CrossTenant-AuthSource: DM4PR10MB8218.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Oct 2025 19:37:57.9056 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: lKby9rGHLXysZczw6NounK+icgSwMgfsj+fA9Rc/RUZ3h/QS7QPRvlLm92O6VUgJMr1uJh78+vLQK7zGn9MmNIzgFI8hCMJ8bnThdocWhTU= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR10MB6852 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-10-30_06,2025-10-29_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 mlxlogscore=999 malwarescore=0 bulkscore=0 suspectscore=0 phishscore=0 spamscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2510240000 definitions=main-2510300165 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDMwMDE1MiBTYWx0ZWRfX38trBPTx6HcB 61MPap1D7RUcWQPg12UUhMO1oQaUfF5LU7E0FWRZdUSciY6IloRE0W3WD/CkcWw8AG0AjQJFBtv d6CDGWEBedYlC8k7fCacFem1fZxaQ5vQuo9tgckEBKbPWozsbc6OPkgCCstHHAYk493xhuwGd7t szBhhwA8q12EvcDcPPOhhAFchPU/9WHI/VD3AP2DTzqWju0dcrWfVhbPz+uD0T8/RLGYL2mqOA9 jTTz+pZ1Hbhvuea+4Df/N122k6d86Im4f82ogiA2T9YSk0TwfTxIfHV+vSamiiY1zpA/5P8VELL Up26LENbex+aIi3sLQJ43SjSu/rrNUJoUOrtsNus67Hu6ou+hioXc+NBDY/Tbssjnd/xMnN1Dcg LzrBFSOkBnwa8SZOI8V6wvMsbHkdFXbzAueejhZxpxxM5WTYSac= X-Proofpoint-GUID: vlko4x7sh_Uis-Egc8R7UyFrnytyOYqV X-Authority-Analysis: v=2.4 cv=bLob4f+Z c=1 sm=1 tr=0 ts=6903bead b=1 cx=c_pps a=zPCbziy225d3KhSqZt3L1A==:117 a=zPCbziy225d3KhSqZt3L1A==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=x6icFKpwvdMA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=oa5kyBmxqvc82pAFaiUA:9 a=CjuIK1q_8ugA:10 cc=ntf awl=host:12123 X-Proofpoint-ORIG-GUID: vlko4x7sh_Uis-Egc8R7UyFrnytyOYqV On Thu, Oct 30, 2025 at 07:16:56PM +0000, Lorenzo Stoakes wrote: > On Thu, Oct 30, 2025 at 07:31:26PM +0100, Vlastimil Babka wrote: > > On 10/30/25 17:43, Lorenzo Stoakes wrote: > > > On Thu, Oct 30, 2025 at 04:31:56PM +0000, Pedro Falcato wrote: > > >> On Thu, Oct 30, 2025 at 04:23:58PM +0000, Lorenzo Stoakes wrote: > > >> > On Thu, Oct 30, 2025 at 04:16:20PM +0000, Pedro Falcato wrote: > > >> > > On Wed, Oct 29, 2025 at 04:50:31PM +0000, Lorenzo Stoakes wrote: > > >> > > > Currently, if a user needs to determine if guard regions are present in a > > >> > > > range, they have to scan all VMAs (or have knowledge of which ones might > > >> > > > have guard regions). > > >> > > > > > >> > > > Since commit 8e2f2aeb8b48 ("fs/proc/task_mmu: add guard region bit to > > >> > > > pagemap") and the related commit a516403787e0 ("fs/proc: extend the > > >> > > > PAGEMAP_SCAN ioctl to report guard regions"), users can use either > > >> > > > /proc/$pid/pagemap or the PAGEMAP_SCAN functionality to perform this > > >> > > > operation at a virtual address level. > > >> > > > > > >> > > > This is not ideal, and it gives no visibility at a /proc/$pid/smaps level > > >> > > > that guard regions exist in ranges. > > >> > > > > > >> > > > This patch remedies the situation by establishing a new VMA flag, > > >> > > > VM_MAYBE_GUARD, to indicate that a VMA may contain guard regions (it is > > >> > > > uncertain because we cannot reasonably determine whether a > > >> > > > MADV_GUARD_REMOVE call has removed all of the guard regions in a VMA, and > > >> > > > additionally VMAs may change across merge/split). > > >> > > > > > >> > > > We utilise 0x800 for this flag which makes it available to 32-bit > > >> > > > architectures also, a flag that was previously used by VM_DENYWRITE, which > > >> > > > was removed in commit 8d0920bde5eb ("mm: remove VM_DENYWRITE") and hasn't > > >> > > > bee reused yet. > > >> > > > > > >> > > > The MADV_GUARD_INSTALL madvise() operation now must take an mmap write > > >> > > > lock (and also VMA write lock) whereas previously it did not, but this > > >> > > > seems a reasonable overhead. > > >> > > > > >> > > Do you though? Could it be possible to simply atomically set the flag with > > >> > > the read lock held? This would make it so we can't split the VMA (and tightly > > >> > > > >> > VMA flags are not accessed atomically so no I don't think we can do that in any > > >> > workable way. > > >> > > > >> > > >> FWIW I think you could work it as an atomic flag and treat those races as benign > > >> (this one, at least). > > > > > > It's not benign as we need to ensure that page tables are correctly propagated > > > on fork. > > > > Could we use MADVISE_VMA_READ_LOCK mode (would be actually an improvement > > over the current MADVISE_MMAP_READ_LOCK), together with the atomic flag > > setting? I think the places that could race with us to cause RMW use vma > > I mean, I just spoke about why I didn't think introducing an entirely new > (afaik) one-sided atomic VMA flag write, so maybe deal with that first before > proposing something new... On the other hand, it's going to be difficult to get compelling data either way as will always be workload dependent etc. So since you and Pedro both bring this up, and it'd be a pity to establish more stringent locking requirements here, let me look into an atomic write situation. We'll need to tread carefully here but if we can achieve that it would obviously be entirely preferable to requiring write lock. I'll dig into it some :) BTW I do think a VMA read lock is entirely possible here as-is, so we should try to shift to that if we can make atomic VMA flag write here work. Thanks, Lorenzo