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 C4A2BC83F1A for ; Thu, 10 Jul 2025 05:25:58 +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: Content-Transfer-Encoding:Content-Type:Subject:References:In-Reply-To: Message-ID:CC:To:Date:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=aqxSTeGUHubH9RxPvXQxf2Bef9n1lFFVG57Wk9BlCDU=; b=tW4arob2H2YNjX oMSIgR6NSo2BRi7mTcYBZWRvz/1QXD+Mtwo7gQJWI/zibtOLsxhQjA9I5Htg3uYJIINHME6RPmy78 Su+H6zg150xzRrA2ezaexDEItmOTi8c7lOljSE7gUSVpAm8j8PokEBCwFrkIngf0YPf7OMsBo0T7N Bljp5Hi1Nz89RgwEMIC2b/VMSRAhrQlpsBH14ig4UbRgp+1PaHzfiiOhVXr9KBu5GT+vX+/UNSv2S fZbQDW6GIFfLulPIS27YiZTlwE6ednW9taq9YK+8eRR/BV1ZJpJdUxau2E7X1ediF1i0vs2uhFhKJ 6HhIPKBJneUGfvrQgQGw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uZjn7-0000000Aich-1IBU; Thu, 10 Jul 2025 05:25:53 +0000 Received: from mgamail.intel.com ([192.198.163.17]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uZjkl-0000000AiPR-2rBL for linux-arm-kernel@lists.infradead.org; Thu, 10 Jul 2025 05:23:30 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1752125008; x=1783661008; h=from:date:to:cc:message-id:in-reply-to:references: subject:content-transfer-encoding:mime-version; bh=bI2YcP3JpX8YLM9eZ+Tjbd1pkRKEVYJKiuxjkAsvF6E=; b=H4SRkcGMX6F80XbY+6OQXnOHXbfMmsxpXjafwXoRrBZlqCGNfdub+4SD W7Yy1UNZrTIGBVJg5KTBeefqpoq3JcJTmlEiy/Tr4f/puzmVMjfLBbsb5 u78/cxivYp1edVlNvGPXinvkG+9pEE8RhPfFfxlfjh3IhPeT8AKK/TgiY KN+Kvpp4lsiK0cNDipns8yKvS3wVnv3Ju6S3ley0Wi/l/4AtmVVnVqzrV wYCGb1231NsDtGjCY7yzxJJZfmZhiyhjszK0bscA+BT3oUO04N0u7LKik ITbfBitqrRut7nlpMuFHsE94m2/nL3kO0WAPL6uLqGZ+nLWDZxehA06dS Q==; X-CSE-ConnectionGUID: KAeSW09/STyxie8qLDkyLw== X-CSE-MsgGUID: BmhWJyooR5uIa2zyFiLn0g== X-IronPort-AV: E=McAfee;i="6800,10657,11489"; a="54323296" X-IronPort-AV: E=Sophos;i="6.16,299,1744095600"; d="scan'208";a="54323296" Received: from orviesa008.jf.intel.com ([10.64.159.148]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jul 2025 22:23:27 -0700 X-CSE-ConnectionGUID: j2HXu1B0QrahPx+rrCaz0Q== X-CSE-MsgGUID: t4iJJxeXRxWs9TPp+dTWgA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,299,1744095600"; d="scan'208";a="156453411" Received: from orsmsx901.amr.corp.intel.com ([10.22.229.23]) by orviesa008.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jul 2025 22:23:27 -0700 Received: from ORSMSX902.amr.corp.intel.com (10.22.229.24) by ORSMSX901.amr.corp.intel.com (10.22.229.23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.25; Wed, 9 Jul 2025 22:23:25 -0700 Received: from ORSEDG901.ED.cps.intel.com (10.7.248.11) by ORSMSX902.amr.corp.intel.com (10.22.229.24) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.25 via Frontend Transport; Wed, 9 Jul 2025 22:23:25 -0700 Received: from NAM12-MW2-obe.outbound.protection.outlook.com (40.107.244.81) by edgegateway.intel.com (134.134.137.111) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.25; Wed, 9 Jul 2025 22:23:24 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=P7GaO9PPEYX+4VUTK9R4D8KbcW9iyvVIi/0GR4OGL9XaJLRmlUuCSC4W+ADEyl+eMm6laLvnTF5Fj7tZ25WZmZQXd3AlpPVTHUXakAWUJhmBchO0/0Hx0vaQtG/XhdaiWomKfGArYW1VNJrwvVfmYqDVMPCIC6TULFfKephKnozzX890s2sFZ5CdnBZLeUmszzpRWb+eHrpWQv/fG1xsM7eCKBOHTCp71Pu+2pcBJlG+KMoWavM4MYWfTfkZ53NKBDY7KJw6WaEly2ebxSShI9rNzBZoCbe1Qp4kp+YF/5OMqpAA0CMl1qQHoFqBp+Hf471MgK5XhRFnCJjDxYRCew== 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=aqxSTeGUHubH9RxPvXQxf2Bef9n1lFFVG57Wk9BlCDU=; b=ynnps9TvpR1quBvjDDTGbZR8cgaYZJs+6kY7yAPvzKLLLb6XWZyuUmUnWvq95PwpO7fAPdaoOm8k9cVeYggvEITQGJROnRwSF/R1omD607+XZNKe3WrZAcRZbohSWauZApFcHqmVVynD8iyIzj/dCllxdimwMOkoWruCID4sYc70kd1/i2Kr0oyagrqG+Wbn+lc7uY1sh3vaACS1ADaQXbFlZrIk9KJKVZLh8WnfmT4mRnQekf7UMIKW6srW94Hy/L34I7w5N+sRa8Usl3l5uuvza+J+EwQQ/LNngpn1hUs8TU7VypR1SJkZrv/XRz5iLWOsqWo/WwZ+upAakR+KMQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=intel.com; dmarc=pass action=none header.from=intel.com; dkim=pass header.d=intel.com; arc=none Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=intel.com; Received: from PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) by PH8PR11MB7992.namprd11.prod.outlook.com (2603:10b6:510:25b::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8901.29; Thu, 10 Jul 2025 05:22:42 +0000 Received: from PH8PR11MB8107.namprd11.prod.outlook.com ([fe80::6b05:74cf:a304:ecd8]) by PH8PR11MB8107.namprd11.prod.outlook.com ([fe80::6b05:74cf:a304:ecd8%6]) with mapi id 15.20.8901.024; Thu, 10 Jul 2025 05:22:42 +0000 From: Date: Wed, 9 Jul 2025 22:22:40 -0700 To: Peter Zijlstra , "H. Peter Anvin" CC: Jonathan Cameron , Catalin Marinas , , , , , , , , Will Deacon , Dan Williams , Davidlohr Bueso , Yicong Yang , , Yushan Wang , "Lorenzo Pieralisi" , Mark Rutland , "Dave Hansen" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , , Andy Lutomirski Message-ID: <686f4e20c57cd_1d3d100b7@dwillia2-xfh.jf.intel.com.notmuch> In-Reply-To: <20250625093152.GZ1613376@noisy.programming.kicks-ass.net> References: <20250624154805.66985-1-Jonathan.Cameron@huawei.com> <20250625085204.GC1613200@noisy.programming.kicks-ass.net> <20250625093152.GZ1613376@noisy.programming.kicks-ass.net> Subject: Re: [PATCH v2 0/8] Cache coherency management subsystem Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BY5PR04CA0020.namprd04.prod.outlook.com (2603:10b6:a03:1d0::30) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|PH8PR11MB7992:EE_ X-MS-Office365-Filtering-Correlation-Id: a0736f00-90e0-47c4-4148-08ddbf71cb8d X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|366016|1800799024|7053199007; X-Microsoft-Antispam-Message-Info: =?utf-8?B?S0pXT3BBWjRpTFROWGpIVDVuTlZiKzJEUGZZM21zQTlnQytIdlBGQU1yWm4x?= =?utf-8?B?RFB1WFhQU3NnNUE2NUlCRHFGWkpIK1BIaWZNWVhieUdhbnJpNGlscWtBNDZC?= =?utf-8?B?SW9VdmNYNnBZZ2FrL3VRWVlPWS9nUng2S0l1YVZOL2pjWW9URVZVdUk1V0xL?= =?utf-8?B?NFBKOEQ2d1E1VmhnVmJUcnhaeUN3aDNCaTlzYzJxNmxoVEw2VCtBdm8reGpy?= =?utf-8?B?clBOQUZyRHBveEFnUjV3M043WVEvQVY3VFlNTXRrdDA3VTR5aWhXaWNzM1VB?= =?utf-8?B?WTl0RW01MnVjYWhWMG1QOGFpaHM4ZDRLWGNBUmZYS2dDN2VOa1hnOG9NSEl6?= =?utf-8?B?eW9pTWlpV2RhTXV4THhXcklNb0VKbkovbTZGajcvWjUwcjBLelpRREJCb1RS?= =?utf-8?B?RUtQV2FrdFF2MzIvZ3N0ekJ0VjNxbjlNdWpXSXMrai91MmdLWm82bkZmOGNN?= =?utf-8?B?RS9PS1RHc2JobEFRUmpPaytiaDdma3ZlV3dqem9QT1oxWEIzZDhYcU9kMDRO?= =?utf-8?B?OUF4MmJ6S2Fnd0pxS1g2OUl6bER3YXYrZHRqNUNjNk1XOG1Bc3lVcXpzRnVJ?= =?utf-8?B?RThUNmV2R0sycTk4cjZkY1NVb0RpSWJaRzZNQmVYVnhleklpdkErNThOc3pX?= =?utf-8?B?bEQ0cTVpUmpaWldzVmIzd0NNMHlmM2s3OW51YVRWMjBvbzlNS1ozYXhJYnRR?= =?utf-8?B?WE9xWC9zMWpvV2F4Y3F2RjI0WGFrRmFJdU1BOC9DVGlyT2RHUFAxYUFCcnZ3?= =?utf-8?B?RDFkak9RdlAxRnJZWVBhblNqdytsNGROV2JBbFl4YzlXMTNnUG9CcitibHJl?= =?utf-8?B?OGhVcFhaNnZCK0greFZQaDYvT2VlWWozMjFydjNaQVpuNlVTeU9iWFc3WXdE?= =?utf-8?B?Nm9pL2xJa1p2WkljS3ZoeHgyVlZNU2tvdmUzNmszS0pKNEZobXpTQ3lhWlY2?= =?utf-8?B?UGdjYm54Y3diMGlCRWNvaDZyeVRvdk5kRXY1WDVsSHNqcHRaOGVhSkI5OGpi?= =?utf-8?B?UzE1aE5UREwrZUw1Um9LaU9lQThjbWZrVUNwZU90K0dwUmNaak1CMzRtZGZN?= =?utf-8?B?c2VqaFlEN2hsd1FyQkw2T0wzODhoRVM4dEg3alZrSzNaVXA3bCtVdmJhVFRa?= =?utf-8?B?Z1BOQ0tEN1RLM3VhMVUrZHZ2TFlrejhJWFd4dktOa3o4SjNMVU9vVitsUU1E?= =?utf-8?B?ZVIvWk0yeW9oL2hZNjZtdmI0TVRqb29WU0VIc25nSks4Rk9tK3I4Rm5ZcU04?= =?utf-8?B?b2d4UEE4UHhHMEJZY1cvOWVjdHVsdm94L3R0QVdQdkNmUEtybDRKVzFmVHNZ?= =?utf-8?B?Zk5pd2dGc01DSExqbUZSV0JrRTVIbVB6Znp2bDRLL3ErQzhBdzU0R21hSVUv?= =?utf-8?B?ZG9OaEhPaFJvTGQ0c3dvNFJwQUZaTzJXQk9SWFpwbU1XME9HVHZ0akkzSmw3?= =?utf-8?B?dWlIeXZTdFV2MitZaVFNS05oWjd6cVBDOW9MNWEvWkRXMVUzUENxRndxaHFn?= =?utf-8?B?SUQ3Q2wwZ0JXSGJSUjNvNFJ1RkhRN3dDL1NwVmpjeDBzanpJSm5qMVRMTkV0?= =?utf-8?B?Z01mSGRmdWZadVFKTHo3eTBQRjhVNFRlRHVCMnVlVU5BYlJzVFBHNk4rNUl1?= =?utf-8?B?Z2ZROUpsb2NhZEUzQk00OG9vT1NZWGtMRUVSbko5ZDViLy9qR0h5dmo2c28r?= =?utf-8?B?bjdZTUlleTlhaTFTWHFTeWZvRkpZbXRZc281OEJXcWo0NFN3WXpVWDZ6aVlX?= =?utf-8?B?cGEvRWlZY2dGQklibUV0amxqa3RSd1NjMFk3dncxVDh6R212aS9WQTVQQ25a?= =?utf-8?B?MU5NVTZTeGpHbFRVMThEM3VPbVZXTWt5dXk0TkdTOXNFQzUrVldMbUw1V25Y?= =?utf-8?B?d2x2aWd1RkJmUjREU01kL1NGT0ZHM0EzdG5rZ2FBRkMxNHJ5bG1sQ2lOUUZX?= =?utf-8?Q?oMPQL68vRtk=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PH8PR11MB8107.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(7416014)(376014)(366016)(1800799024)(7053199007);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?TTFxenpwcDZxeDJ4ZFEwVmhNUkZIM3l5VUk1THg1KzhTVHRzOWlzNVY2d1BF?= =?utf-8?B?eFFtVmFENjFxbmR6Q2gycVk2TE1JSEZBOTIzN2k0bjd0aFdMZzZUOEZqR3Js?= =?utf-8?B?YkkyMnc3KzBIMkNES3dEdmpUYXEwVCtjaDUxc2RXanFQaFFNNEVtcm82OTZk?= =?utf-8?B?UkZTa3FWUDN0K0RlL3VSSXFVOTVIYW44YTd3MDJjTU1zdGxKdTlZeXNaYmVU?= =?utf-8?B?d3FDSEMyMUIvRmRXaVB3QVo3a2ZUUFZEQzVWK3hGZnZFdGtHMnZHdm1uTk45?= =?utf-8?B?TjFmbFFlbFJOZURaQ0xUSE9JVndJc2xUMlkvNnZVMkVlQk0rVFp5ajllQk92?= =?utf-8?B?RjZraDYrQ2hxb2pjNlV6U2ZVNit0Qnk3Rnpzc3ZNZGttbTJIZXFyN0kvUUMv?= =?utf-8?B?TUZObWlIZEU3OVU1cStNbTdzNDM4Zm9jMUFNU1hwcjFMbFlUVXF4cmdoYjdN?= =?utf-8?B?N09hZ0tYTWI1aXRITzNXamF1M0lMZnpBM1JQTVN2TGd2ZzFJR3RNUFovNTBI?= =?utf-8?B?VTcwQ081elRZcHpDM1FmMzVwekJLeXllRHdxNGZrbWZKZzkzZ3NzeW1OcitW?= =?utf-8?B?SE5KU2IwbkdpSEl6NWVFMnBMbzZTN0lvM1lXOHZtU01KVlVQcXRWYVJ6U0hO?= =?utf-8?B?Ymk3Z2M2TnpObUFhR04xRnIzV21GTlo1dWxwMmVEUDZmMk4yeGpCVFhveDZl?= =?utf-8?B?T2t5RXpJT0dwZ0VETmJtSUdsMVE4UG00WDJacTV4TU56alk5M01VQ0VYeTlE?= =?utf-8?B?NDhvMi9TUkFQUVNqblJuL2pjS05jZ0RjdHNLUi9YQ1J1WHdJdFFVajFTeVVB?= =?utf-8?B?aUlReVRPc0lDNEJJSW9nZ2Z6TTlQbWtrVXR0UFd2SzByWGU3MXhhdzRDSzd0?= =?utf-8?B?clE3a3pIdVgzZ212ODgyVlV6UUdvQ09LdGZZaEdWUDhUajAwNzdZVXVaODE3?= =?utf-8?B?REIzbUhHS1dnbm1UM2xHVHFiS0Y3Vkprbk1MZnRXa01KWXgvWXc4Wlk3VUdK?= =?utf-8?B?UmpuNHpnei9pUVhFVU4wWnZJdGJlbGk2M0xHQkZjclk1b1NjbHp0U0ErNzhI?= =?utf-8?B?a25xM24xT3ZSa3NRYmJxTTNHRWNKcUtFazRxWlh4dmwzL3h1dlczbi9wb3BJ?= =?utf-8?B?TFZYdWhZRGFLMjhVcmFEZEQwZHlNR0xobUpsUU1qdyt1QThkK2dNTXJCQUVr?= =?utf-8?B?MjdvU3lWZjNvckJDaERIMlFPZUxFRVkwVWgwU2wyaTZRU3pqSFdDM1Z4QTJJ?= =?utf-8?B?a0l1V09ERW5KeXNYT2JSckdRVUlMcjJiVmV6enFyMjROT2FuM01ybWtMd1Ix?= =?utf-8?B?VjRzcFhlaXR6WFpMLzN2YzJXMCs2M0pmOEdQUUtYbWwzRzgrMXovT0ZmRjRO?= =?utf-8?B?T0ZnUHR1YWlrOXpqTU5KR3k3VzV4VEpxRzJiMjFsREJ0K3VEUkRPL2M5SkJJ?= =?utf-8?B?WUtZNEpybWo5RGFaM1VLK0hpRU9LeldDcGgveUM3Q3Y2blJ1NWRuSmVGMUxI?= =?utf-8?B?ZkNTdDBoR0hQcWdQUjExMFFrUDJIS0pqUFYxaURuQkNsTElVT1JNeUkyQnJ2?= =?utf-8?B?OVpkc1pnejJlMGl3WmlYNklKUkx3ejkrekMxYmRPZTNBZy96dFpyeDhkNHJK?= =?utf-8?B?eUpVN3lScUZhdTAyb1VSM1Z1UHUyVzNscytJdy91clNlL3Bib0JMcW1rN2d3?= =?utf-8?B?Q2NCZkExMDB3L2RBRFMvT01LeFRodG90aEFVUUxkVTZLNHdBcFU2NzJjOGhP?= =?utf-8?B?alppVCtVUkVYMEhPKzduMUpXOGZxWUx2VEU5Y3J2RFNkWXRnd21NNFNXSVho?= =?utf-8?B?YzFwS3FLOE1nWGJtdjUrcEhIMUNxMDQ3Q1h4YWlWemVDR1FYRkJLK1k5aXll?= =?utf-8?B?ZzF3NTJrTGo4QW5SekJDeHE1VlpwZndoVUhXMlU4cndJZ0x0aFVkZ09zWEpS?= =?utf-8?B?NmJMZG9leXEwd1M1ZHN1ZjVZcEFsVVNnSndNZVVmWlhYVjJOcW8wanBFeVpz?= =?utf-8?B?U1kyZ05tRTVUdHBRUTUyYklzYTNBZzBvV2w0d1BtNWhVWXB4MWFxSXZzYk9Q?= =?utf-8?B?NVdnNExhb29MSXg2cElVTjB6b2c5d1dGYnVpWXl4Mks5b1IwU2tXcWhCVHBZ?= =?utf-8?B?QktCTnlaRllYK21teHJQNGRvNUNWM0JMQ0F2U2paMjBpUlVvTEg2M05zNW9G?= =?utf-8?B?OWc9PQ==?= X-MS-Exchange-CrossTenant-Network-Message-Id: a0736f00-90e0-47c4-4148-08ddbf71cb8d X-MS-Exchange-CrossTenant-AuthSource: PH8PR11MB8107.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 10 Jul 2025 05:22:42.6179 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: WQEUmBjfRr1+y7wrJiFaDiaRm41tEvq9U7R1YwlIsbLtlKsL9BSzL47hmspzh903JVXOpnChGMDTE1jUccBRbyw+DjwlLWUa4xYy9JMzb/8= X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH8PR11MB7992 X-OriginatorOrg: intel.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250709_222327_774942_861B75B3 X-CRM114-Status: GOOD ( 32.50 ) 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 Peter Zijlstra wrote: > On Wed, Jun 25, 2025 at 02:12:39AM -0700, H. Peter Anvin wrote: > > On June 25, 2025 1:52:04 AM PDT, Peter Zijlstra wrote: > > >On Tue, Jun 24, 2025 at 04:47:56PM +0100, Jonathan Cameron wrote: > > > > > >> On x86 there is the much loved WBINVD instruction that causes a write back > > >> and invalidate of all caches in the system. It is expensive but it is > > > > > >Expensive is not the only problem. It actively interferes with things > > >like Cache-Allocation-Technology (RDT-CAT for the intel folks). Doing > > >WBINVD utterly destroys the cache subsystem for everybody on the > > >machine. > > > > > >> necessary in a few corner cases. > > > > > >Don't we have things like CLFLUSH/CLFLUSHOPT/CLWB exactly so that we can > > >avoid doing dumb things like WBINVD ?!? > > > > > >> These are cases where the contents of > > >> Physical Memory may change without any writes from the host. Whilst there > > >> are a few reasons this might happen, the one I care about here is when > > >> we are adding or removing mappings on CXL. So typically going from > > >> there being actual memory at a host Physical Address to nothing there > > >> (reads as zero, writes dropped) or visa-versa. > > > > > >> The > > >> thing that makes it very hard to handle with CPU flushes is that the > > >> instructions are normally VA based and not guaranteed to reach beyond > > >> the Point of Coherence or similar. You might be able to (ab)use > > >> various flush operations intended to ensure persistence memory but > > >> in general they don't work either. > > > > > >Urgh so this. Dan, Dave, are we getting new instructions to deal with > > >this? I'm really not keen on having WBINVD in active use. > > > > > > > WBINVD is the nuclear weapon to use when you have lost all notion of > > where the problematic data can be, and amounts to a full reset of the > > cache system. > > > > WBINVD can block interrupts for many *milliseconds*, system wide, and > > so is really only useful for once-per-boot type events, like MTRR > > initialization. > > Right this... But that CXL thing sounds like that's semi 'regular' to > the point that providing some infrastructure around it makes sense. This > should not be. "Regular?", no. Something is wrong if you are doing this regularly. In current CXL systems the expectation is to suffer a WBINVD event once per server provisioning event. Now, there is a nascent capability called "Dynamic Capacity Devices" (DCD) where the CXL configuration is able to change at runtime with multiple hosts sharing a pool of memory. Each time the physical memory capacity changes, cache management is needed. For DCD, I think the negative effects of WBINVD are a *useful* stick to move device vendors to stop relying on software to solve this problem. They can implement an existing CXL protocol where the device tells CPUs and other CXL.cache agents to invalidate the physical address ranges that the device owns. In other words, if WBINVD makes DCD inviable that is a useful outcome because it motivates unburdening Linux long term with this problem. In the near term though, current CXL platforms that do not support device-initiated-invalidate still need coarse cache management for that original infrequent provisioning events. Folks that want to go further and attempt frequent DCD events with WBINVD get to keep all the pieces.