From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.18]) (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 03D3829A5; Wed, 18 Jun 2025 00:49:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=198.175.65.18 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750207754; cv=fail; b=XcPkKx+41dUO2EzVGNPST6QAvziQ8pM88ZZHdcXy6DKbT1iO1VVailDPruljigghABT0ikrb8+aHfxMSvuRGZp5ESJtuiRY4riJhouJBu465q7UxZ+FDtjx5boS32AnYmtYRLMVpX/tZCp67R+xJjVcArSxU6lZybKvZHqToNNw= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750207754; c=relaxed/simple; bh=6LsIxNh+Ilf0i2odmclnNWAa1QyLSC8NWnbUk6lZ3jg=; h=Date:From:To:CC:Subject:Message-ID:References:Content-Type: Content-Disposition:In-Reply-To:MIME-Version; b=J91X7ebQiGiIBD8Ligqw2jvCJbGD1BjCwtFNFV42jwdGAkkRZRLQ5CHTQ9WodkGJKW4hJlHKh0QoJf8zn8my0BkUJyiSDYfiHG8l8XpFd0gNaq/NhUfHJe0zxJGDoq1BRCuU3NdJhIdn2mdwtJUkb45N2AadgsByshPjfDT1G+A= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=VShbyF3i; arc=fail smtp.client-ip=198.175.65.18 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="VShbyF3i" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1750207753; x=1781743753; h=date:from:to:cc:subject:message-id:reply-to:references: in-reply-to:mime-version; bh=6LsIxNh+Ilf0i2odmclnNWAa1QyLSC8NWnbUk6lZ3jg=; b=VShbyF3ii+uxDbB8KEUt1VDxFRd3pSYn90MMMX0rMlrZkaSJnG3f8Nxo xd/oZ0t6jyuH2WmU/d6h411bzlHWjmuSr0nm5bFfZBP7WafFWD2R7xZTB 38OvKrH85xc0SBu/1alBbl4eSsHMXqye9wlhDnEMqf/6Rm2lFsGxU+kXS IZbKp5O0Z3oHmribnQ5g/hepzl47H9F+PB36K0x9zcjwpt7adOzb2MidP 7eOUWIgyhpNuEqMmf2YycFHCigyHf1T2kiaSU3PxUdzNtjq41mKKvfQyA RKE3SR33d97FPpgcyj2TkyJDfMMZu7fg9RNawxpL92E0suYdOmeZtz9/q g==; X-CSE-ConnectionGUID: Y5emcCmoSty3fdpACDpq/A== X-CSE-MsgGUID: PzTADg39S0aKwneV62NYDQ== X-IronPort-AV: E=McAfee;i="6800,10657,11467"; a="52545940" X-IronPort-AV: E=Sophos;i="6.16,244,1744095600"; d="scan'208";a="52545940" Received: from orviesa009.jf.intel.com ([10.64.159.149]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jun 2025 17:49:12 -0700 X-CSE-ConnectionGUID: biVM+rTmQ5OYOhBG/uidYQ== X-CSE-MsgGUID: atqq3SlVQWG9vP+uKh3JnQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,244,1744095600"; d="scan'208";a="149039614" Received: from orsmsx902.amr.corp.intel.com ([10.22.229.24]) by orviesa009.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jun 2025 17:49:13 -0700 Received: from ORSMSX902.amr.corp.intel.com (10.22.229.24) 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; Tue, 17 Jun 2025 17:49:11 -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; Tue, 17 Jun 2025 17:49:11 -0700 Received: from NAM10-DM6-obe.outbound.protection.outlook.com (40.107.93.49) 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; Tue, 17 Jun 2025 17:49:10 -0700 ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=kLI72PIY89PGWHeinRPti4RSA2irRD5getd5Crf41KAMRNc4J9hA5jpYnle5F/LpATKiA6rvotfObCFnI4VI6x0B4dXX9eYCvgpRYnTLOdXxFm9yF7p3AHueyBrTKtK3iNZb/V476p6MyqmANGOpU/kFbi3ox3E5x3f1zPNjMX1JbSvcKh4sRtK8Ue9ju8nz6/xsXHPqtF0y826hF2l1s21tCm67sdFMRU6y2dj9OnBZiLFUjp5e8s32Ip6/ZPcQSJgpSWkhSZ50ZXbv/EBcVGF9AeywnB54UB4+TlL/2/p8RZNE/GTu23My4lvdphNCfBLX1+uPmrxPAf+TsfV80w== 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=q9g3fMwoKhbmZGkjsyDjUFqen3AmxTl8nrQJ1XqBmFk=; b=cKo+51xvxMNhfHbsyERizWFtJDP2Yo+CpakZBbyOnCvo73nFEmFyL+l1j0REl2UpkUHl1NYh4lY3biNjJnE4RofdMi+gy/kI8il13LWcLXxVT748ApfZWyJui6Zsf3lmUwVlV4CCV+rlakT3eekMV1yoaG3JdC8abpj36AXqZOr0PQWQoNameFT+R0iVjEXngs+nMxX8aD/PpTJwhREELOhgv6Rv55/Xju0KUKKHcfPWWcy727KSJZoiExUHUal+K9dISzgMDbbwct1h23GO6QF3bQt3Lj4uhA3dvFB+hd3pK+/PoD5aFPt90cnTmMyriXhn4Kas+eAlASu0la/GRA== 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 DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) by SA1PR11MB6733.namprd11.prod.outlook.com (2603:10b6:806:25c::17) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8857.19; Wed, 18 Jun 2025 00:49:07 +0000 Received: from DS7PR11MB5966.namprd11.prod.outlook.com ([fe80::e971:d8f4:66c4:12ca]) by DS7PR11MB5966.namprd11.prod.outlook.com ([fe80::e971:d8f4:66c4:12ca%5]) with mapi id 15.20.8835.027; Wed, 18 Jun 2025 00:49:07 +0000 Date: Wed, 18 Jun 2025 08:46:38 +0800 From: Yan Zhao To: "Edgecombe, Rick P" CC: "Annapurve, Vishal" , "kvm@vger.kernel.org" , "quic_eberman@quicinc.com" , "Li, Xiaoyao" , "Shutemov, Kirill" , "Hansen, Dave" , "david@redhat.com" , "thomas.lendacky@amd.com" , "tabba@google.com" , "vbabka@suse.cz" , "Du, Fan" , "michael.roth@amd.com" , "seanjc@google.com" , "Weiny, Ira" , "linux-kernel@vger.kernel.org" , "pbonzini@redhat.com" , "ackerleytng@google.com" , "Yamahata, Isaku" , "binbin.wu@linux.intel.com" , "Peng, Chao P" , "Li, Zhiquan1" , "jroedel@suse.de" , "Miao, Jun" , "pgonda@google.com" , "x86@kernel.org" Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages Message-ID: Reply-To: Yan Zhao References: <8f686932b23ccdf34888db3dc5a8874666f1f89f.camel@intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <8f686932b23ccdf34888db3dc5a8874666f1f89f.camel@intel.com> X-ClientProxiedBy: SI2P153CA0034.APCP153.PROD.OUTLOOK.COM (2603:1096:4:190::17) To DS7PR11MB5966.namprd11.prod.outlook.com (2603:10b6:8:71::6) Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS7PR11MB5966:EE_|SA1PR11MB6733:EE_ X-MS-Office365-Filtering-Correlation-Id: 758ae282-d771-4187-c799-08ddae01ee7a X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?hupciZtNO+BcDJv6lCW7GJXiolDNuxgQg0fKkAMFUkJ0zI5JihGko961JuXB?= =?us-ascii?Q?xwpbM9wkTPX3wyNnEhC3aWrfow9ilV3Tpyf1aq75T+NJwtVqmP8YTQyabMGl?= =?us-ascii?Q?QOUE+NO57HAFfxoYEqJ6CHUF1wISP4pkivdbQlBIgNuIzUm2UuqjVszMwxb6?= =?us-ascii?Q?OrRuzy0wcea/vwJ9oiCuX2HxidUD/71ACjc7yOV21laZNqOrJlauEzvyVej7?= =?us-ascii?Q?FUZBvTjDcSqca+xGUUCJwjrFxr6N1Wlamdl96cszuNmT6XLeOdqL4faILmHO?= =?us-ascii?Q?vZfpWQ4hxDMijg+oTVDBr47Kc5mcwELQc0tB1Vhj5l2eJeGBFi0cdrnqlFOn?= =?us-ascii?Q?vGapOH472pR1X6XV72tiVZ/lFdE2Ps8IvF8djaUM+MG5+/78GtX5HyOUlIPJ?= =?us-ascii?Q?L3mkDnAHfBCR1fRg9c51ah+km2gUVOirZrLXQV6hHkNaFU9S/lZxR2XmJgIB?= =?us-ascii?Q?IglIv41TcvEwJXvaeTI3OeRxv4CX1ByrKgRdzF4d3T3PGQ0YpPd0Ey2UJXrq?= =?us-ascii?Q?MvdGfySwOZ+VtOTIYv+zNY+Eg/v5OiXjCWQZcs13VXvlpTSUJ8r2+tyrNIF/?= =?us-ascii?Q?9l53QI0aq/aPr/pLcGzxJRbguHcuSQLEJyJ/MhCwhesq9TE9/WKZctr9hxqI?= =?us-ascii?Q?OQmZ0GgQ/OLBnwF5GVSYc7kgKeGramifsGKardJ7Byy2sly1Qn5cRoD/vTr6?= =?us-ascii?Q?U7+vo1vNeLcPtIUePjXsCSjtlFAYo0Yhn1gDgviI3ze+U78cosgUbmSuuUgn?= =?us-ascii?Q?wjvs2RRHt1/VOoMnzVJ7WsdEGGrdKhchkimqE3R6BXd3r8qOsxizjykJkDJ+?= =?us-ascii?Q?MUzAmX9Jbmq99/aE8nPx3h9KHxaP+k81iR0/Z1CkgaDwE1ltuX65PtDykPzd?= =?us-ascii?Q?ir/UGL8a8vB/UewhxS49H30iTlbRIe8fU2Kl1eejG4k5jMTQZUVgPg4/CxYG?= =?us-ascii?Q?/k4My3uZK+yV4hJZVKUiUJF41L+8juugH79ARo/O5M+mXTm7tLpUZ+iGIVZx?= =?us-ascii?Q?D5BFCVxEtIrrvwsuwyTtdojvfLs68Z7e9UkCIB7hOGL6ePdOCCzcMLcsIGRj?= =?us-ascii?Q?lK3YUNytymccY4FHrUfrgvbfyZ6qZU9zQHtY2TpQpEowsg3++pFW9olO9uT5?= =?us-ascii?Q?xB8s/8jLewBSwzFKpEupS5rPygOUuOXX1nD2QZR7gLWzLo8zthZkgvyd0T3f?= =?us-ascii?Q?jDPzyAuUgxzqTZulPKekvC1Eaj/n767DJ84AcSbj0KriCEdkwyiy28XeJZUV?= =?us-ascii?Q?yAcvjPjCfueq4fQpBnjC1n0W43MLykAXrhuF1GNBFbThbU67dMrHsFLT0OlK?= =?us-ascii?Q?kihClFqE1DuFxHP8f2v3NhkKndi5UyA/5vglGXJOg+BcvD639FUoSuYQgjto?= =?us-ascii?Q?Mv60ybGAuTTWT+kppJ3f3bBgwN1q51ynF55xHORcz2PPJTMoywx5tZbv4xrh?= =?us-ascii?Q?Zx5E5Fkmbqs=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS7PR11MB5966.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(7416014)(1800799024)(366016);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?qNHWYU6/JXNsRYAI7TTFqT1sI9ZJol0BiDGpku1zkWKYaSV6YS6o1Ihug0JA?= =?us-ascii?Q?PuGrkKczw6SZMJnw3WqVIIZq7irMEpQ06xSN9CQ6hTnqO9RWyO7+HmeExkA8?= =?us-ascii?Q?H7bGEbtGtYHRQ8tx7Nswa6XMJlLt6SJFI7CI1FL9+Z52JolVnS6857k8y5+M?= =?us-ascii?Q?DcDzn4wVJ1pL802lBsJZ2FDNvAxSFsm2P/8k5Fi6VI0vnuBQt9ikCv/VAz6i?= =?us-ascii?Q?/3gDWwEuusHC8nb7D0ye0Dc8/I9z4zuPzY9HbUBTjwTXH2dmyYJVa+8w3rI/?= =?us-ascii?Q?Cyy9yIV56kNVXGOclpAfzYhdBQOlIhhqEd4schwhbAOVzxLDlFxP+A6CI1wR?= =?us-ascii?Q?BitZSeXEphrcAQkQywnk87rEq0ww234PzatKYZWwz3ZDcWWDiuAMB7oTaBZv?= =?us-ascii?Q?hKXp6hDSmPk97CiptFrsOTS0mBlx46iuZIsh8Ik0UMeWRdFZ2iypp/Kfmzfh?= =?us-ascii?Q?l98hJUwvqzcBG69XiEzZJgfBfkYdfVgis8y130Q/f4twiTOaQKSwKePzZjTC?= =?us-ascii?Q?4N0By8gXhPLJPzVL/Edd8XgoKJaXYdd2Dbbv/zdVpPZh70pTDi9F8JzLqPmv?= =?us-ascii?Q?ozmKLsUhOuZL2sFmRK7K2KdN1GZoQDmWMIzAMAjjJgx7wCeSujMBdiVwzNbQ?= =?us-ascii?Q?cGtAMWaxnjsAsb9WY8Inwcxd2PXUmE5Al0ZdzWuOVVZm/JvZKuJHPnv1YaDT?= =?us-ascii?Q?VNtXXlMjrGq6+zioQrVYnEZoth+mxNTJFvdGt22OAwW8BVnImGg6oPj6f6ZH?= =?us-ascii?Q?uSRhaD+nENXb9O2Z7T1I8SISRtr+vx1PVlKZ5pGb68V+nfi/3bY5RuDasqw8?= =?us-ascii?Q?xBaOpjojlpUV7JMCkmmzcptvo6iykZsiyrVV7mBesRLyNnlrXHyFB5hpPRs9?= =?us-ascii?Q?Me4Th/g2S5OJtxWH+BVZ23JdAVIVbR00W7vqyUZrin7Dh192QqpLiNYuaCac?= =?us-ascii?Q?cxJ4QtDov2+vpU6WbkeyddOHz9YEhycdLp5gDyIZQLVHzye6W5kqguZF7OIc?= =?us-ascii?Q?KLo1vPPt3fl9JD7ntKl6Pg2bqxUJD3/kFTynDhcp2r3cG+U/rq6RUMlsn1qc?= =?us-ascii?Q?DBIIIkkp+5kNgKLlmPHmM+2iu/0GQLrDbf9peotNyukQ3gpd/hXsRuGKPQlp?= =?us-ascii?Q?jOER3Ne5dhU/MX1QTupG4lMZdpRT6kZKJ06Pzo9/uhOQh/uIYfMUpeRhA/bw?= =?us-ascii?Q?eCDPr/fq0RRzeQyj0het16WzgWtP9xC0Xl9JguRsSWIX9ESHa3XqoIankwlD?= =?us-ascii?Q?hiVycu3+n2pz7faWAjhUkUTsjCrmhNqZDJCTNZUFsRiUn/JAuzEXpOQqJ+Es?= =?us-ascii?Q?/NbzKSz7FAaoe6lJ5u8daheRZf2PseVU8OCbaoeqfoIStsLWPQ6IvQqENdWc?= =?us-ascii?Q?Y8PbIZlhJGW4g4q9/8Wf6hBZssm7WlMF3vtsBi6PflvawFxkoVgxbPmAe2f8?= =?us-ascii?Q?Z4hhp969Hhs9o7L2ivbiEFK3TjYD6NMd4B7awU2ccOcY/wKGaF3AymzSIp/4?= =?us-ascii?Q?1gtpgVDFyGZMbQMBIpHlpPXyw0y68YKLybTMHxgFA4ljXdqIwH6r7012ZApY?= =?us-ascii?Q?HoaOydBt0tfPzC16sKgdePHjPHSrL+yOUNX5Y3DP?= X-MS-Exchange-CrossTenant-Network-Message-Id: 758ae282-d771-4187-c799-08ddae01ee7a X-MS-Exchange-CrossTenant-AuthSource: DS7PR11MB5966.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jun 2025 00:49:07.7019 (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: iICzd5kGl6FkH7Dq2wYZN1Hdpjasi4P8yWH5fcnbLHaq0d7EmHWCyktcJYpR7jePaFhlCrzgvh5D34eigozNVA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR11MB6733 X-OriginatorOrg: intel.com On Wed, Jun 18, 2025 at 08:34:24AM +0800, Edgecombe, Rick P wrote: > On Tue, 2025-06-17 at 01:09 -0700, Vishal Annapurve wrote: > > Sorry I quoted Ackerley's response wrongly. Here is the correct reference [1]. > > I'm confused... > > > > > Speculative/transient refcounts came up a few times In the context of > > guest_memfd discussions, some examples include: pagetable walkers, > > page migration, speculative pagecache lookups, GUP-fast etc. David H > > can provide more context here as needed. > > > > Effectively some core-mm features that are present today or might land > > in the future can cause folio refcounts to be grabbed for short > > durations without actual access to underlying physical memory. These > > scenarios are unlikely to happen for private memory but can't be > > discounted completely. > > This means the refcount could be increased for other reasons, and so guestmemfd > shouldn't rely on refcounts for it's purposes? So, it is not a problem for other > components handling the page elevate the refcount? Besides that, in [3], when kvm_gmem_convert_should_proceed() determines whether to convert to private, why is it allowed to just invoke kvm_gmem_has_safe_refcount() without taking speculative/transient refcounts into account? Isn't it more easier for shared pages to have speculative/transient refcounts? [3] https://lore.kernel.org/lkml/d3832fd95a03aad562705872cbda5b3d248ca321.1747264138.git.ackerleytng@google.com/ > > > > Another reason to avoid relying on refcounts is to not block usage of > > raw physical memory unmanaged by kernel (without page structs) to back > > guest private memory as we had discussed previously. This will help > > simplify merge/split operations during conversions and help usecases > > like guest memory persistence [2] and non-confidential VMs. > > If this becomes a thing for private memory (which it isn't yet), then couldn't > we just change things at that point? > > Is the only issue with TDX taking refcounts that it won't work with future code > changes? > > > > > [1] https://lore.kernel.org/lkml/diqz7c2lr6wg.fsf@ackerleytng-ctop.c.googlers.com/ > > [2] https://lore.kernel.org/lkml/20240805093245.889357-1-jgowans@amazon.com/ >