From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from DU2PR03CU002.outbound.protection.outlook.com (mail-northeuropeazon11011062.outbound.protection.outlook.com [52.101.65.62]) (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 EE93B477E57 for ; Wed, 21 Jan 2026 08:33:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.65.62 ARC-Seal:i=3; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768984428; cv=fail; b=IZznMvhdebtnQ/Z7AmsYjFkucwQUVJJVQagP03Fgp1jPR7+benQZn3yna7xyNQyPJI3kO9n3vhR2pA+s/STntGBum24Ee5j7o7Fvz6xAciETaHl+jTITAOxg29kDNatQiYYOpg8nblxG2cns/lPsWzehpdAMxbduZk61mJghK28= ARC-Message-Signature:i=3; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768984428; c=relaxed/simple; bh=630tUyQ7cTJdJBtTCJv5gthmJBWYpYigO/DMA/mKWuA=; h=Date:From:To:Cc:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=drt5XOxYaRUWZGmiujKQ6+WKR2h2JoBgMg5tMBKsh85jfr9vnVIjueTdNJMS0A5UhC7d0ayU+czLtDfFKSWeKyQCPftzMevOtjvvJazP+fhJnZMcGwyZtGnPzEG22+XIP3yNBlfPGobCPOjPIs5GPVBZnSn1fH36lLbvxhMtIY0= ARC-Authentication-Results:i=3; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=lKx0iBfS; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=lKx0iBfS; arc=fail smtp.client-ip=52.101.65.62 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="lKx0iBfS"; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="lKx0iBfS" ARC-Seal: i=2; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=pass; b=dwCM52slr4px+fIY19TnQJvsbPeRHgFDj8QuEOzpdkCblBMge1GhKBnzPFHos14i7KLkW/BiBtKTBUnbb6hcIw7yqTcPkUsR6+DPb94wQlx2s2GiHW6h8aEupWqhrRpk9va9OB64xgJQcKcL7jFmVAbaK8Ga3/4bnsytuSM8Agb5mgiuIXD+1K3xs9D8AsYCMRsvmtOyEn93Exx0xiWT+j3bFu09eAyBAI2VputXVq7Ce1rpfzdDhohPT/bW+FzRU/BTdQDlW20lH99UBYg32p3WcgJMHHQ8CmFAKbce5d9+gzNg6luzOFqDHVqXB3wIvqEebYUTcm8J5zwYwFrdWg== ARC-Message-Signature: i=2; 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=630tUyQ7cTJdJBtTCJv5gthmJBWYpYigO/DMA/mKWuA=; b=tQmeBdiXzfkN0kpgpb4i+fiKxBIK2h+PRMsE/Nc0vZRtsL/s49/2ni2jcBj+IdUsfOzeSP7nmoETKGEtnJxgDXAxugyQJS+UafLzYgrXUIXHqetPqWQBtEQZ0qay/KYK1T+8ax8T06rWGrSJJqo68qWrbl1ZmCAQZqRGh9ckVFQRBgugTZVMiA4HD8Agk0s9pNZQqXtv5r5cFG1elHJOL2CS1GOEeOnWrBE3H1292TG9Rlf/p+qMMWQgLgm5hB88831eQ/6ftYej2q8YxcxPSITFiU4UzhMVtuTViCtbs8YOPvgVwbajaOpSqMaR4GzMK48bHtli2Y78js41ZCt3TA== ARC-Authentication-Results: i=2; mx.microsoft.com 1; spf=pass (sender ip is 4.158.2.129) smtp.rcpttodomain=os.amperecomputing.com smtp.mailfrom=arm.com; dmarc=pass (p=none sp=none pct=100) action=none header.from=arm.com; dkim=pass (signature was verified) header.d=arm.com; arc=pass (0 oda=1 ltdi=1 spf=[1,1,smtp.mailfrom=arm.com] dkim=[1,1,header.d=arm.com] dmarc=[1,1,header.from=arm.com]) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arm.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=630tUyQ7cTJdJBtTCJv5gthmJBWYpYigO/DMA/mKWuA=; b=lKx0iBfSKR5UwNH3cA+Ld/Zfxj+Qf6NQvC/17lXJWuzhZNF2zCRQ5A+9IEKJnUw8x5Xvo08HREI3TW9E44n/tBn84qUuQgyMR4NqOIrsl0WRgSmpJTvscBN9/NSt3j7AXcBOP8aBKGT9LaZfsfSccSkpaCDchLEadjnCXEC4s10= Received: from AM0PR10CA0032.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:20b:150::12) by VI0PR08MB11515.eurprd08.prod.outlook.com (2603:10a6:800:2fc::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9542.9; Wed, 21 Jan 2026 08:33:40 +0000 Received: from AMS0EPF00000199.eurprd05.prod.outlook.com (2603:10a6:20b:150:cafe::6c) by AM0PR10CA0032.outlook.office365.com (2603:10a6:20b:150::12) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.9542.9 via Frontend Transport; Wed, 21 Jan 2026 08:33:32 +0000 X-MS-Exchange-Authentication-Results: spf=pass (sender IP is 4.158.2.129) smtp.mailfrom=arm.com; dkim=pass (signature was verified) header.d=arm.com;dmarc=pass action=none header.from=arm.com; Received-SPF: Pass (protection.outlook.com: domain of arm.com designates 4.158.2.129 as permitted sender) receiver=protection.outlook.com; client-ip=4.158.2.129; helo=outbound-uk1.az.dlp.m.darktrace.com; pr=C Received: from outbound-uk1.az.dlp.m.darktrace.com (4.158.2.129) by AMS0EPF00000199.mail.protection.outlook.com (10.167.16.245) with Microsoft SMTP Server (version=TLS1_3, cipher=TLS_AES_256_GCM_SHA384) id 15.20.9542.4 via Frontend Transport; Wed, 21 Jan 2026 08:33:39 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=Yd4RjA+nlcAQz9/z8HoEE1GUEuDtWX7hTX66W7JHWAWIoGZvn+01wQwabxbT7Gc0tjFkKt8IYJQ9l9xglux+FBD3xGNZfZbd6oLsHRAyy5lan0l7t6caYrvE4/HbNDwi3QbYOa84NSFZCYFBn4oSwRPar449K64ZbuvHuV9dlPvj26WiDrH0AndXQ4N0f0rXo4V7my8gjNKSTwBbO5fTIhJMbrE6KVSoS8OUdTfUmPPYZwnUBdrAPSCyvsUsIPIgJtMuOSHvh1AntL2GMnd9xuRD473xuMDkp7f3Hx/HDLBxjEmrzuokPnYGwGUjICp3TmC6+f6UNBS4AfhHUkO0AQ== 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=630tUyQ7cTJdJBtTCJv5gthmJBWYpYigO/DMA/mKWuA=; b=JxeP9jHTuPI0NcAOMxrhXAShytACxF7G6OERBcej6wkbiZx53rgb+9DjGTygGWUXa7pjySUwlNEUl9u45Bro1Kl+V3Dw1/N+UQdZtzv8I/2Coe4syaZsbzLkX53s2l+W4z2RJiStj6Er7Yww0DUmVpog51nBTZiiBeIyaJ/BSLJMACyglMVFQQ26zFZIONqNbI5hBpIKiNBqaOGG5VtL9UW7cbP+6YazeDR3SdY4IVbB/t9TNDffPKB96LsQBWY3IwgFG4/yTcUE0Vt0XrVydgpijchobF04CB1rnF3LQgs1C9VLjW9K06T9aA6cd9odtFvmkCVg+khXRq9VvKQAdg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=arm.com; dmarc=pass action=none header.from=arm.com; dkim=pass header.d=arm.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=arm.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=630tUyQ7cTJdJBtTCJv5gthmJBWYpYigO/DMA/mKWuA=; b=lKx0iBfSKR5UwNH3cA+Ld/Zfxj+Qf6NQvC/17lXJWuzhZNF2zCRQ5A+9IEKJnUw8x5Xvo08HREI3TW9E44n/tBn84qUuQgyMR4NqOIrsl0WRgSmpJTvscBN9/NSt3j7AXcBOP8aBKGT9LaZfsfSccSkpaCDchLEadjnCXEC4s10= Authentication-Results-Original: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=arm.com; Received: from GV1PR08MB10521.eurprd08.prod.outlook.com (2603:10a6:150:163::20) by AS8PR08MB8995.eurprd08.prod.outlook.com (2603:10a6:20b:5b2::21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9520.14; Wed, 21 Jan 2026 08:32:33 +0000 Received: from GV1PR08MB10521.eurprd08.prod.outlook.com ([fe80::8c9b:58d2:2080:eb98]) by GV1PR08MB10521.eurprd08.prod.outlook.com ([fe80::8c9b:58d2:2080:eb98%3]) with mapi id 15.20.9542.008; Wed, 21 Jan 2026 08:32:33 +0000 Date: Wed, 21 Jan 2026 08:32:29 +0000 From: Yeoreum Yun To: Yang Shi Cc: Ryan Roberts , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, catalin.marinas@arm.com, akpm@linux-oundation.org, david@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, dev.jain@arm.com, chaitanyas.prakash@arm.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, lorenzo.stoakes@oracle.com, ardb@kernel.org, jackmanb@google.com, vbabka@suse.cz, mhocko@suse.com Subject: Re: [PATCH v5 2/3] arm64: mmu: avoid allocating pages while splitting the linear mapping Message-ID: References: <2619166b-13ef-4daa-82c7-1d44035a8d6c@arm.com> <11a01f4e-9ae5-4001-9f9c-74a746f898cd@arm.com> <02bb61cc-f0be-41e5-b8b2-59768afd5254@os.amperecomputing.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <02bb61cc-f0be-41e5-b8b2-59768afd5254@os.amperecomputing.com> X-ClientProxiedBy: LO2P123CA0020.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:a6::32) To GV1PR08MB10521.eurprd08.prod.outlook.com (2603:10a6:150:163::20) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-TrafficTypeDiagnostic: GV1PR08MB10521:EE_|AS8PR08MB8995:EE_|AMS0EPF00000199:EE_|VI0PR08MB11515:EE_ X-MS-Office365-Filtering-Correlation-Id: 7f5220a2-4cca-443f-a6f9-08de58c7c75d x-checkrecipientrouted: true NoDisclaimer: true X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam-Untrusted: BCL:0;ARA:13230040|1800799024|376014|7416014|366016; X-Microsoft-Antispam-Message-Info-Original: =?utf-8?B?WDJMOTJMZHh6eDJxOFBWaldtd1hBakZFUlp3bjFHeHRhdW4yM1JuKzZCUWh3?= =?utf-8?B?anRoMlNZVFZqV3NEWEdqTnk4RkFvNHZ4NnZMYzhlcUpXdngreS9NYlRuZXNK?= =?utf-8?B?d0VRcHk3elpiWGw2ZlBMRWNhTDZaSzM3djRkdjRUZVArdkxySjJYZURqSERw?= =?utf-8?B?NVcvS2MrcmJjRG14VkNEcjZoaFhZZDV5amtMcFpxQ3I1UkV2b25GK3lGT09Q?= =?utf-8?B?QlJVRFRzM3NYWnVCMUVOVGRWRVdjQUVNNCtCeWFURTdNdnBWQkxzL1BtV3BU?= =?utf-8?B?TDZveGR4TXZ6T3FjTnlid2xmT3Buelhyb1ZmQ3RVQ2Z5RXVwQlNNVjRNUkkz?= =?utf-8?B?WVB6RlhvOXovbkpteEcrTVJNUkExRUJJZ1Nhd0RMcHBZZGNlc0Z6ZG16Z1lX?= =?utf-8?B?eml0WERLZFV0a0gvVlYyQTBIWENwd0s0bTZRaDExTFIvTEk2RWUxc2U5UVVw?= =?utf-8?B?V25aYzJyWnBlRHZiOXZpaTY0WDNVNGJmSktROVJCK1pPTVF1L0M3SG11Qy9z?= =?utf-8?B?YlE3YnpoVEIxdkc5aDlXTFY0VE42SzIxNktoU1BxKzdEMTdMWjRXL0Z6bDlp?= =?utf-8?B?eW85bkxINVhEZVhWekNxdld0SzhvRGdpdWxIZzMrRERxUlpZZnlTRUdtWjBi?= =?utf-8?B?MXZWNEtBRFhTR2RkbVpkanFOWjJGNmxSejFsZWxuMk5IVGxkL1M5d2JTeVpr?= =?utf-8?B?RnV4MFpzSm1PUGVlTlhrMmF1YVhES1Y1VjN2SmVsNmhnQmtmQ0hFQnVHN1lQ?= =?utf-8?B?NkpRdGlTNU5yRkZ6aDFLREc1eStJNk9OOEtwRmx1WkNIYXNWb3RCTTA2dU9P?= =?utf-8?B?UWRwZTBUTm9adDRBTllJMERoS1NxRS9GVEhtTFpKRkFRdXQwOTVobG9OUnNn?= =?utf-8?B?bXNCZXpYWkdHeEVTYUZMeTBPVFlNSktoSmozR0dCNFZoRDZNSFVwankwVDV4?= =?utf-8?B?MXpuVXJRb1JsRGxNSTI2QXFFYWdXTVRoZ0dlNXQ1Q2YvaktKeXN2U3ZNVlFu?= =?utf-8?B?NTRPek4rTmdMakl1SlRKOG1Ic0xnTEFPM01kbENpeDNWTTVad2ZXa3VHblpU?= =?utf-8?B?T3gyL3lxZTYyQ3M4WUo3NlZXWVhzOEo5Z0JnN25WaER5MmZvUXVRMWJOdVZS?= =?utf-8?B?SGNkbHV3WlU0eEJ5cnRMa21VOEpKTmxVbTNHRkdCWklVeFRKb2VpSTkvdWVX?= =?utf-8?B?b2ZQeDkyMWU5MkpONlZuM3UwQkFnRGU3UnREYkhzT0RxK1FMaG5wYXhzcE1S?= =?utf-8?B?UGFTZmlsK2IxNkJ1UHIvOFZWM1lWOTNXaUYrTEF3ZXR6cTdvT2pzNklwVEpX?= =?utf-8?B?NTUrRXhXTFR5Q2Qzd01HYlMwYWtiRzEweDhadkdyWVpscUVWY3ZpSEJrY3lH?= =?utf-8?B?VkdaT1ZWL2IyUDN2d0Qrc2ZGZzJYTmhFbW9wb1pWYWhJT1A0TkE1cnJrREpQ?= =?utf-8?B?amJaOHNlRE5vclY3eG5ZSGhxelZjcVRFVDRpc1RvNEZxeWRsUHpsMTZIQm4v?= =?utf-8?B?TldsTGo5VHVXb2RFaXhRYjYwdllkTFlRN2loa2Y5N0NBNlBYU2krelphZm1C?= =?utf-8?B?OUtEaGJWU2g5L0JVWXNnRDh5em9EOHVjczNrdzdkODhHYm9STkhYUW12MXFh?= =?utf-8?B?eWxMMTFGV2pJOWZxRElJbmI4UWlwT1l2Ky9qK1FGSG9KK25VOUR0ZmE3bGp2?= =?utf-8?B?VVMwZnBNRWVmcXVUdlBsOGVaNFcxY1JnVjJkUkNRM3REclhpbWNLdnJFeTBL?= =?utf-8?B?OGhpT1VJS0JMTnljeGFER1Evc0Rhbmc1RVN6R3hLbFV4bGR3c1JTVG9qdTBn?= =?utf-8?B?cjlzNy9xSVhqazU1NGJ5eHg2eDc1eFh2YWRkUit5N3lGU0hpMEx6UFJYdGlu?= =?utf-8?B?cThsbUVlKzM4eDdhTGpTSDlWSkFoanBhbUtiUjVTWlMxQUxtVHMrVkw5V1NR?= =?utf-8?B?WndydURFNk52ZUJKdGJ0OTRHd3NqRXR2dVdrbHd3Kzk3eUgwWm45YndkdExV?= =?utf-8?B?dE9ETHA5L0djVTRLM2FsRS8veXNTdzdiVjYxSHgzMS9LZU82bGM0T3RyR3Jk?= =?utf-8?B?MXIrZ0ZKbHlrVExqMDduNUtpUFd2T2xVWGpVdFpremZXb0tDRjFtOW9qMUpM?= =?utf-8?Q?0V5Q=3D?= X-Forefront-Antispam-Report-Untrusted: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:GV1PR08MB10521.eurprd08.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(7416014)(366016);DIR:OUT;SFP:1101; X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB8995 X-EOPAttributedMessage: 0 X-MS-Exchange-Transport-CrossTenantHeadersStripped: AMS0EPF00000199.eurprd05.prod.outlook.com X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id-Prvs: 00bd09dd-9f69-4642-52d2-08de58c79f8e X-Microsoft-Antispam: BCL:0;ARA:13230040|14060799003|82310400026|1800799024|35042699022|36860700013|376014|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?dFBYc2s0ODFYYVBXVThuN2Z5aGJXdENIRDkrZVExQTZxUlV1Zzk2SWRiQ29K?= =?utf-8?B?WnVyV3hVS2J3SE5OOFhYUXZIY1VGVjhEQlgzUDVFV2drcGhKNjc1VzBHZWtN?= =?utf-8?B?dEpmRW5QT0JNL1FiSjBCWGhkYXNod3VQbmE2UlVod0pCMUU0aHphZFMwQWxN?= =?utf-8?B?ZW1nVUprMkYwN2M2YWhGTE9WTlBicndBQVRzUWVRUkxsUFRncFdZU1IwZE1J?= =?utf-8?B?NU5uZXl4UFNtMnpaOUNhTDJaTy9zQ3R1ZEsyN1ROYUFZMk9SWGl6d0cwQjRK?= =?utf-8?B?MFlFUUJMYW9SSjQ1OHNlK1NOZW5KeHYyRlpZcTJpZThvY1hCUEMwTEFYM00w?= =?utf-8?B?QU16WmswNjVlZEx6aEIzK0lCQjZhcS8zcTJFci9td0JoQXNlUzlYUmZhUGdm?= =?utf-8?B?WDZadjhTbmFldzM2elA0NFJRTjM5RDFBODVVWi9LYWwzZGhFYktBdWZKNVV6?= =?utf-8?B?OE5RY1FiQ2Rod3ZDbG1Bb1E1UDZpS3lCZU5Qa3Z5Rjl4ODMxUG5ObERGOWxo?= =?utf-8?B?K29DcDBhcUhNU3orM2E4K3NpcVk3T2JZZGRnQWdJdGN6aytCMkZrS3A1ODBE?= =?utf-8?B?bHBIdnpMSWJSQ3NxUjE2WUIvcTN4dVR3cFl4TE5XQzdNLzhkRWpycFRxMW8r?= =?utf-8?B?a2RJT3pOME9KK1pIcHp2cEhlUnpDNlV4Q09PM0gyZmNvRjAvdGRLZDVCY2ZL?= =?utf-8?B?Z2FhWGJWR3JrdFFaYmtlNVFzZzBKRFhvZzFQV3Y4MVZGNVUrZjRSUkI1WnUx?= =?utf-8?B?cXhZai9LNFNVVVEzZlp3U29CazJoMmpvZnNCVDFTcCtxVVF5aXU5enYweVJh?= =?utf-8?B?SEExamY1SWtLRm01NEU1akovRjdOcFB6bTlKVk4yYy9ueFNJRCtPRUMwb1Rw?= =?utf-8?B?ZjZqcXVIYkVmRjg1R2o0ZDdKcWVleEtzZWgzdzJNWmF3a0d5Qkx2NzR2Qno0?= =?utf-8?B?TVlzdG5FR0ljQzFyTzc3bWo1YlU1TXZxQVFvNHY4R0lUZ3JUdHZHQzlHWEhP?= =?utf-8?B?WnJ6RUcvRzhvaEZoZUc0RTdobUZid05SbEpWM2V3YWxtMlhnSXA5a2FWSFRq?= =?utf-8?B?eWpvV2NVMHEvWWd2QkFxSDUzSUhEMm5HZGM1SkltY1VQdWxzbkZlYnc0OGw3?= =?utf-8?B?SWNDUmpsNDhpZzRqSXY1SFFxdjlSekZOMVBpTjdSckdsdWIrTEpvd0FXY1cz?= =?utf-8?B?ZU90QWpmS3VrN0FOc3JiM0JJUXluVncxbkllaWdxdHVNekRyWHZWWndQdzhr?= =?utf-8?B?LytYb1c2Z3hPbVRYY1B3NEhKVnA0MlZSSk1kVGpwQlE4Njk3U1pyY2FFU09I?= =?utf-8?B?YmRUK1IxNkhKKzNUbXJmSksyNlMwV3ZDMWVlOXhqTG9sWWxOKzJBd2ZPd3Q2?= =?utf-8?B?WlpnQ20wZXZReEpMSHZOQ1NyTHhWdTg0VFJkOUozY1cyZjNlMTkwb3dKSHlS?= =?utf-8?B?NHJOcmw0K1pXa3Z3RU4ydlNHNWRKZmpUNnZqODNTZW5SY1l3cHMwWmxaTjJX?= =?utf-8?B?eXZpR0hIbG9PYis5c2FKTHFjTHFCRk9xQ2g4d2xhOUpDUzg3QWFCb05EaFdl?= =?utf-8?B?U3VQRTRFVmNWLy8rcXdUbWF3U2Z5TWZ4RmV2alVoRHF2dDVjL0xMZ3hYcVB4?= =?utf-8?B?MVRQVDM3YlJLQ3JoeExIUVhFa0x6YjF3TTAxRVExNTRnbTdUN2IrV0RVdnhJ?= =?utf-8?B?V1lKNjJkWnJ5UFcwYUlUTzU4NDFNcGJnL0Z6SFBXalVKL2pyN1dZQURna1N3?= =?utf-8?B?dkRYUXc3cVNnNytpL2pEcGx3TytQUllxbkVVSTBFS1pFU0p4SGpxYVkwUXJH?= =?utf-8?B?Mzc5eHBodGlueWdGYzRWbmxPUTBRcWFHUk5WVFo3a3FZSnZaYzl6dTF1UkE3?= =?utf-8?B?RmZWM2toUTV6elVEdDNKRXpKT1BsaUdkcTV0NkhsLzRJdTFxMG1pYXJLanVG?= =?utf-8?B?N3ladThrNjJIS1g4L3pHS1FhWCsvZE12UlR2N0pESytwaGR1UVVONUJvZGxy?= =?utf-8?B?RFFHR2NIS2NvREpEdUFwWTF5S0s3TjgzU2hqcm9VZHRZa09SMm0walRCWHFY?= =?utf-8?B?MWpVWHhhelIzRCtPdWcydFNhaktlRUdwR3d4K05sUmIvblBwSS9ZcmJVR3lo?= =?utf-8?B?a0UvQzhqZFJ0Tk4xVUg0VzcvTTNhem1ITDB1Z0NMVkF0UVFDZGlTQ25pYmU0?= =?utf-8?B?Q1Q1a2ZJdEZYUlhScHFlVlR6cXFQZVo4ZkpyeVdDWDB1WnJPUDU4cnhoU2Ez?= =?utf-8?B?aUVoRzBieVNyUjc2Qk0xeHhUQ0pBPT0=?= X-Forefront-Antispam-Report: CIP:4.158.2.129;CTRY:GB;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:outbound-uk1.az.dlp.m.darktrace.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(14060799003)(82310400026)(1800799024)(35042699022)(36860700013)(376014)(7416014);DIR:OUT;SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jan 2026 08:33:39.8788 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 7f5220a2-4cca-443f-a6f9-08de58c7c75d X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF00000199.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: VI0PR08MB11515 > > > My concern is that if a secondary CPU can race and cause a split, that is > > > unsound because we have determined that although the primary CPU supports BBML2, > > > at least one of the secondary CPUs does not. So splitting a live mapping is unsafe. > > > > > > I just had a brief chat with Rutland, and he agrees that this _could_ be a > > > problem. Basically there is a window between onlining the secondary cpus and > > > entering the stop_machine() where one of those cpus _could_ end up doing > > > something that causes us to split the linear map. > > If I remember correctly, split_kernel_leaf_mapping() does call > system_supports_bbml2_noabort() before doing real split. So we basically > should fall into two categories: > > 1. bbml2_noabort is supported on all cpus. Everything is fine. > 2. bbml2_noabort is not supported on all cpus. split_kernel_leaf_mapping() > just returns 0. Kernel doesn't split page table, so there won't be TLB > conflict issue. But the following page prot update may see unexpected block > mapping, then a   WARN  will be raised and it will return -EINVAL. So the > worst case is the caller will fail (IIRC all the callers of set_memory_*() > handle the failure), and we can know who is trying to change linear mapping > before the linear mapping gets                    finalized. AFAICT I > haven't seen such WARN yet. Thanks for the great detail :) I've missed system_supports_bbml2_noabort() in split_kernel_leaf_mapping(). > > > > > > > I'm not immediately sure how to solve that. > > Do we need some synchronization mechanism? If the linear mapping is not > finalized yet, split_kernel_leaf_mapping() will spin. For example, something > like this off the top of my head, > > DEFINE_STATIC_KEY_FALSE(linear_mapping_finalized); > > Once the linear mapping is finalized, we can call > static_branch_enable(&linear_mapping_finalized); > > In split_kernel_leaf_mapping(), we can just do: > > retry: >     if (!static_branch_likely(&linear_mapping_finalized)) >         goto retry; > > > There may be better way to handle it. But this case should be very unlikely > IMHO. It sounds crazy to have such complicated kernel threads run so early. > I'm not sure whether we should pay immediate attention to it or not. Thinking about it again, I’m not sure whether it is acceptable to use a sleepable synchronization mechanism at this stage, like split_kernel_leaf_mapping() does with mutex_lock() (even though it may be technically possible). It also feels odd that this function can be called at this point in time. If this is indeed considered problematic, I think it would be better to simply return -EINVAL immediately when linear_mapping_finalized has not yet been completed. -- Sincerely, Yeoreum Yun