From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from NAM11-DM6-obe.outbound.protection.outlook.com (mail-dm6nam11on2069.outbound.protection.outlook.com [40.107.223.69]) (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 B0E451B4F0A; Fri, 27 Jun 2025 04:50:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=40.107.223.69 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750999813; cv=fail; b=lQQTZYTgvacnJb6nh3BpElpyGJlvKDmSpfpgnUX5gnAaK9PcYpDtOJ/C4Wmjy/ZkaijgnXvhWcdWEd5nnrx24GHtF3T1KurUcjHRhLGv1BWd5475+u4qhDflZmaO/YC5kctNadlXsCwMeNFEKylxtQXAx3PUSa8+QiEWQzKr2jM= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750999813; c=relaxed/simple; bh=TZYwnNBWm01JqQDzmG9VWtpuo/mfncVsOQSDNVZbWCs=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=Q0jEkN/g37rMOAXeRipmLxFWNFY370p39SElOgyGeToTbiSfyZn8y31pHskBXoJi/+vsQbPe3jEVY4vm9dpBTxOdLqb0TTVQES1uuGB7G3ea4D+7UbQvqJ3V7vz8EirCXPKi9kmD6+s2TrVXN4KL3ittlk+JZWmLcP0TCweXV0U= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=WbJAwzc6; arc=fail smtp.client-ip=40.107.223.69 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="WbJAwzc6" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=be9mZW7QwpVQ9qbRppfZauy1dwehRVM5dVK/bgG28AFS8hOtFCIhEXDsGQeb7baTwkydE0/Z5KbuleeDDZcqcmbbWzGTQHBBKVeYyl0uCTM9e8RwZkRL6j359yTd4fP3xxUCza1WIcQdUM/UikcDdL/yKAZe1h5gZTwBws0Av0tbRbWTGccdwKJIPEdH75k8iyntxY5vqBqFSkl5l5i6YAvSkO3xFVas0BK8c4gW8njHyLFPqBf39A4cZ0k/RXbJV/q15qM6cicnHq24FaW5e4uSEEIlIxqmqWr6BDxDvcLBhkel422YehRS2h5lAc+2K1FIesvM7XKeUl2uT4rGVw== 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=ldthRCkoTsD2UKH4NGE7AwlciWimiB7HU90nzQP/XDY=; b=QV9Oxr51uuqS2kPx1FSTghWmbuMK4D4LvGtazHns4EkvoqDMfEgjK7mmKObdLxj2egtUCXn1TnYcYiEequWmh7Sre6rJ5xs5XLfSz2+kCLOL0WFInJjBrETSe7Gk6pVBSqFUNUB6KImIXCH0twJfSzzuDygKbGTjtTYUcE7h7b7gZYRfgRJDzZNrM+K+80Ku3/TA25X3SO+Myu4CUAkNHyXOJf0+ngea1OxbDI9lq/s5EDLwBBCSk2lREnDvzABQB35EW0bXSRgyr2n75baCkFMb7N5cnNZYJcdd1CTINH9Jv25b5jnA80oOZ5ZjDYG6pfniVRVscpWLQrB1ei7H7w== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=ldthRCkoTsD2UKH4NGE7AwlciWimiB7HU90nzQP/XDY=; b=WbJAwzc6FunNaq+PG664LiZg8O48Oc+LGk5n/ttQcPaRLmN7zqeuxOu5aIHwQ/H9AcZMcu5LqDI05OXhmtCSqIFQqYLbJ9HuVEiDGwsiGKUKIhKEfr65zoQGvXLqMu476+AelB0W2mX5v8eroH9DDmFPDp+0rUrTKV6jMSWscuY= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from CH3PR12MB9194.namprd12.prod.outlook.com (2603:10b6:610:19f::7) by SJ2PR12MB7990.namprd12.prod.outlook.com (2603:10b6:a03:4c3::12) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8880.17; Fri, 27 Jun 2025 04:50:07 +0000 Received: from CH3PR12MB9194.namprd12.prod.outlook.com ([fe80::1e6b:ca8b:7715:6fee]) by CH3PR12MB9194.namprd12.prod.outlook.com ([fe80::1e6b:ca8b:7715:6fee%7]) with mapi id 15.20.8857.026; Fri, 27 Jun 2025 04:50:06 +0000 Message-ID: <31beeed3-b1be-439b-8a5b-db8c06dadc30@amd.com> Date: Fri, 27 Jun 2025 14:49:43 +1000 User-Agent: Mozilla Thunderbird Beta Subject: Re: [RFC PATCH v2 04/51] KVM: guest_memfd: Introduce KVM_GMEM_CONVERT_SHARED/PRIVATE ioctls To: Vishal Annapurve , Jason Gunthorpe Cc: Fuad Tabba , Ackerley Tng , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-fsdevel@vger.kernel.org, ajones@ventanamicro.com, akpm@linux-foundation.org, amoorthy@google.com, anthony.yznaga@oracle.com, anup@brainfault.org, aou@eecs.berkeley.edu, bfoster@redhat.com, binbin.wu@linux.intel.com, brauner@kernel.org, catalin.marinas@arm.com, chao.p.peng@intel.com, chenhuacai@kernel.org, dave.hansen@intel.com, david@redhat.com, dmatlack@google.com, dwmw@amazon.co.uk, erdemaktas@google.com, fan.du@intel.com, fvdl@google.com, graf@amazon.com, haibo1.xu@intel.com, hch@infradead.org, hughd@google.com, ira.weiny@intel.com, isaku.yamahata@intel.com, jack@suse.cz, james.morse@arm.com, jarkko@kernel.org, jgowans@amazon.com, jhubbard@nvidia.com, jroedel@suse.de, jthoughton@google.com, jun.miao@intel.com, kai.huang@intel.com, keirf@google.com, kent.overstreet@linux.dev, kirill.shutemov@intel.com, liam.merwick@oracle.com, maciej.wieczor-retman@intel.com, mail@maciej.szmigiero.name, maz@kernel.org, mic@digikod.net, michael.roth@amd.com, mpe@ellerman.id.au, muchun.song@linux.dev, nikunj@amd.com, nsaenz@amazon.es, oliver.upton@linux.dev, palmer@dabbelt.com, pankaj.gupta@amd.com, paul.walmsley@sifive.com, pbonzini@redhat.com, pdurrant@amazon.co.uk, peterx@redhat.com, pgonda@google.com, pvorel@suse.cz, qperret@google.com, quic_cvanscha@quicinc.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, quic_svaddagi@quicinc.com, quic_tsoni@quicinc.com, richard.weiyang@gmail.com, rick.p.edgecombe@intel.com, rientjes@google.com, roypat@amazon.co.uk, rppt@kernel.org, seanjc@google.com, shuah@kernel.org, steven.price@arm.com, steven.sistare@oracle.com, suzuki.poulose@arm.com, thomas.lendacky@amd.com, usama.arif@bytedance.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, vkuznets@redhat.com, wei.w.wang@intel.com, will@kernel.org, willy@infradead.org, xiaoyao.li@intel.com, yan.y.zhao@intel.com, yilun.xu@intel.com, yuzenghui@huawei.com, zhiquan1.li@intel.com References: <9502503f-e0c2-489e-99b0-94146f9b6f85@amd.com> <20250624130811.GB72557@ziepe.ca> Content-Language: en-US From: Alexey Kardashevskiy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SY5P282CA0085.AUSP282.PROD.OUTLOOK.COM (2603:10c6:10:201::16) To CH3PR12MB9194.namprd12.prod.outlook.com (2603:10b6:610:19f::7) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH3PR12MB9194:EE_|SJ2PR12MB7990:EE_ X-MS-Office365-Filtering-Correlation-Id: 2610c285-4e8e-48f4-80dd-08ddb5361664 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|376014|366016|7416014; X-Microsoft-Antispam-Message-Info: =?utf-8?B?MFVGT3E2dWxJbWNEWGNTYVVWSkVUZFRSOExvdlZ4RWtxRjNieFh1TzhsbnpC?= =?utf-8?B?MW96dkEwVWtUK0QyMlI5Q3RxR1dzdk1yckpLRlY3Tkl1TDRDSS9kS3R1aGJz?= =?utf-8?B?ZU1oNjRlM2JwbDNQN0pEa2ZkQU50eHJaM1FRdWZmVVhkRVp6V295TGw1dWxO?= =?utf-8?B?ZFNPWlNTWlgzYXF5NzZUamxLN0lhY1FGWHdtKzlNTWNnUHhxeWVXSW1HWWtw?= =?utf-8?B?NzhPeURIVWt2cEpSeHBNSnVjWHMrUEhaL1JObmsyS2I1RjVrakZmSmtQT3Nx?= =?utf-8?B?THdGTXMrTFhyTVMyWFNtL01WckJJWVJVVjN6T1d2UUNURGdMcDlHVFNZNENo?= =?utf-8?B?c0NDbmcrTFNPbGtjclhQNDAyK1JjMStqa1R2WE9CMmNDVHhBcnNYckFKZG5D?= =?utf-8?B?d0pRd2lycU5JbW1FVGQvdnE5RzZIWWdPUVRQMlVVOVZUc1UrUEY2cU9meThZ?= =?utf-8?B?NysvRm5HZm1lMGV0aUEvT3NFdDFUQnVtZHpMYnk4QW9HenFFc1h6eXZLVUlL?= =?utf-8?B?T3RiZk4zQ2xtcjVsVUlqUDgrWEljS2JDdnF0ZXlMMmFVeGxwMmpMN0swNWV2?= =?utf-8?B?SlIvTzkrTWk3TkxzSDFKdHJrR05zbGhSa2lReEQrK0hBcVQyVGtkTlhXSU4x?= =?utf-8?B?TlBmUGUrelVyYjNUVWJ6R3NEWUN6QWZDV2hmV2pwZWdCTGlrMGVLaDViRzMx?= =?utf-8?B?S2RSNHdtS3grZGx0NnNJS2xVMm1aUVZBVDhHaDFkSHc0YjQrNEJ2alkwVkUr?= =?utf-8?B?ck82K3FBK0VBbzhxYjdLQi9TNjFJZ3o0bktlNEZhR3orbC96WWlsUHYxWlRw?= =?utf-8?B?ZEVYaWh2enkwWTFBU1ZGK1c1MHR4cXNDUjltdUVIT3AzNHJ5NkhQM2xYZjVE?= =?utf-8?B?NVR0QmRURUUvc3l4M0UwN3l1Skh3YmtyZHNySjA2ak1KMUFMeVdxOG82Y0tz?= =?utf-8?B?MVVrUzJxQ1JjS2FwWk42NjdoVExYc2c3cFE1Y0I4eU56a2JLVER3eHRwM2Rh?= =?utf-8?B?NDdoSFc0Z0Y1blRDOUV4V0FXZ2lOdHBlYlVnZllXYm1naTJLK2RpeTA4amxG?= =?utf-8?B?MUxYQ2xpSnloQzR2YzFUWUZFUFozRVBMcUVXRERKaGVONDRVZ3I1WjNJWlNl?= =?utf-8?B?ZHZUejVZdFRtYm5MTkowREQrZjVQYytUTWNLU3RObWt2cE1HeXowaU1SOVJa?= =?utf-8?B?Wm8xbk9TQitwZkdFY1c3VmNoek85RWFKQk0xa3gyclh0UkhXMmZPMVB3ZGhl?= =?utf-8?B?QWZQSnZMT2tlSTBNV0RDY2J3KzZoVlVNV3F2RDJvWlg4NVZTcGIxQ050U0hP?= =?utf-8?B?VWpGTHFvUm93anpMRnY2SkQvM0d4UEdvS1pjNC9Kalp3VGRKOTJqblFGNk55?= =?utf-8?B?eHFwOTF1UmlTUXlyTEpyU3psQ3dwdEswMXAwQno5UG5GVTRaRmtodlE0aVZB?= =?utf-8?B?U2hHRDRJT3BpTFBTTm9saWhuTUUxZ290ZzVyTWxHZDN3KzJ5M01aUU04dVBG?= =?utf-8?B?a3kzSXMzK2JTN2s1dGw3VG1ieGEvNFdhdE1neEhScWpRNXhRT2FnajhHVWpi?= =?utf-8?B?M1FXbXRIWm5LekNMSy8yR3RIWXdHRFBuQVd5OSthdlduay9yemdnUXpSa2Mr?= =?utf-8?B?L0xKL2tmWTJINGFJeDhFdVZpL2VMaXBHcXdhdVJQQmZMZXFYZ2R5NTBwZ2cz?= =?utf-8?B?djgvZTVCZEpxS2RUSDI1YlpzSmNtMHNNdFhjVjE0aWJOcnd3MEtYQThVeEFs?= =?utf-8?B?OS9lNVQwbmFJcFVuWTBRQVUxVkovdDFZTnZNRjV4MktPcXRYQitjQW1NWHdi?= =?utf-8?B?eFBGYU56WlNhKzk5bUJMY2RvTmJjSWwvcktmaDhjbG0ySTJhK2VOUGwzcFp1?= =?utf-8?B?TXphRHdmaFlxQ2t5RXRsbERIdS80UnBMaHR3Z0EweGVHWW5udDlvdzh3Q2Ft?= =?utf-8?Q?wntKXg6rc3A=3D?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH3PR12MB9194.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(376014)(366016)(7416014);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?RjBEaFpCeXBGSTJjcGpMUVFFR296d3hCZXpWVVdxN2E1dE00eGdTODd4b0ZC?= =?utf-8?B?R2ZUMCtaUUpkc05EWjJWMzl5cU9Nc20zRWswcVAzR0d4TVJWcGN0Y1J3OFl6?= =?utf-8?B?YnZEb1VkUDZzQWw2Umx5eWdLd2pKRU1qVXZyZktKNlE2WEhLREY0d0hSZWdj?= =?utf-8?B?NDN5d05RaHh3ejlYNlVHVFhaclk2YjMrbzROQTRjNm5zU001L2tFNU1Rc3R0?= =?utf-8?B?NWJIVlI1QmE4YTMwV1hyaDB2RTFIVDVuZ2Y1V0FIZnZNaVEvV1EyZ3pWY3A1?= =?utf-8?B?WjRJQTFibDFSNWc4RktYVjdlM3lQeHl1Y0hSeHhlNmo4clNyOFdhWXNMMzIr?= =?utf-8?B?OXlmQ0NZMkhTMGhsZ3lDS2E2WTVvdzZ0RGhPbmIzRkc0VWNIczRPbFZCUEhM?= =?utf-8?B?UzdhaFJqTUpKWHdTbWNGbWdyUFk0N0tFWnNENjF0TmZhMy94TURFdE5EWTZx?= =?utf-8?B?UE9ZQk9GV1FLbmlQejRoZGRRM0Nkd09NTFljb0plM1hNbW9zY1JRVGF2T0JI?= =?utf-8?B?MHpGMlEwelgvQmFMdnNaNzVSUnFvS2lueE5mMkI3VmJSem9SNnFmTHdYREk4?= =?utf-8?B?b3NYQkpFMTVWbEZGb0JlWklyMHZPempxamwrd0RIemFOTTI1eGMyTDNDbWho?= =?utf-8?B?V0xXaEp4TktGZTdqWFlUWjFhMXpIb2hkc2tTMVoyaFZNK3JMVDlac1F3czBM?= =?utf-8?B?VThpckJmMzJaSDJiWWZYbFZZUkdKYmJZNzlrTkh3OGYxbkJOdmp1SHlsV2xv?= =?utf-8?B?ZU5DNlMxR0laRytxbDJjaHhJK0t1WlhXYmVad1h4Wm5BallKeWNoWW92S3NV?= =?utf-8?B?RFhxenNKZGRaYk1PUmtEekRyc2pBTDM1YUVjeVdsK1RlWG94eXBndmRSWXcy?= =?utf-8?B?UU1YbnQ4UkFvSWU4SE9HOWswRUhiRDIwZVFvNkNCWjc3anJVeFpISHpVWGdO?= =?utf-8?B?OXFrWERCMnBOVzZyZVhydVQzUFFZbm1ab2U5V05VMGxYajFJVHg5R25sRTdM?= =?utf-8?B?UDlHZ2tGOFVVUDkyRlZZSENXVGhvbVROTzBPczE0OE9hVEUraTQyVDh0Ynhm?= =?utf-8?B?a1RXMzFFanVyNzRXMU9GcjNSLzg3czdwU1ZpaUdhQjBEMXJQZlpYMVVlYmNC?= =?utf-8?B?VHQwTVMyYVBLMG5Jc2N4amU3WlFKcEx3TUk2aEF4QnFraGFpSUlzKy9XMUcz?= =?utf-8?B?Qm9uVTBWckNjNWhQVjROdHFrZlR1akJSbjN0MTFNSWhQdUk0NG1zcWlvdVNk?= =?utf-8?B?bGh4SnkyODRXb0NZZVk2dGh2eDNYL002Vm1hS3FwaFNHd3EwbWU3VUFmVExW?= =?utf-8?B?R09LUjNQUERQNnl4OS9pUjBsSG1iSFRXVllZY1pPR1Eyd0NncG0wWnZmaDh0?= =?utf-8?B?RlFHalZCOEx5cFJjbXVjWWpXalQ0eFVWN2FrMThwWHdGNGZtcDJ3Y0hUc2pS?= =?utf-8?B?QThQazJmcjVQZVJBT01uMnplRTJ3SE9uRU1mSVdYVkhBNm1KUWVDOGdJYkow?= =?utf-8?B?a0JBQXpRK0V0VDFGejRpVlNDSDgvMjY5VlZJdEQ4allvQkNLVWJJZGhxYnFy?= =?utf-8?B?OEttajFkUHRUYTdvaG1ZcTlMa0VzZkJINXR4QkJKY25QWVowWXBuVWhBQ2Nv?= =?utf-8?B?dWlTbWN2R2t0Mi9kYnRRL3BXYXZHby9qeUlJTUd3WUJWZFpmUVJlWjNkcVgr?= =?utf-8?B?TWtJQzJyQnRvVWtONzY2LzBzMmNSeDlkbVU0OWQ1cmNTVUZkNGpBUXIvWmNx?= =?utf-8?B?b0VzckhhZVdvTU85OU1oNWllN2hURE1IWXpVQ1dZeXVETjB5Z2hjYVZrT0Vo?= =?utf-8?B?Rmh0SzdwNDBRSDNZSk8yV3FMZ2llZ0xPUHVzejhhdnhEWGszSGo4OGZZcTBo?= =?utf-8?B?ZVd1Zkx5d2NJT2paa1dsK1lVaUQrTWdGK2VFOHh1dDNJcldnaFlVeDQ0M3lH?= =?utf-8?B?UGlvelJyYmJpa3lSbTBydzJGNlVtN3JzMUVoV3ZBcjBjZVpkNWNnbDcvLzNL?= =?utf-8?B?L1NwZjVOZmljcnRQUDNFVXNCN0Z6aU5aODIwM2ZibTNtQ2ltbitxYzRTemND?= =?utf-8?B?R1FmL1k4aTZjbjJGbWJIaVo2alB4Rlo3YnNqY2lVM1Jyd1luWjJ2YS9na25a?= =?utf-8?Q?1timBcrJpo96qmMNuFGPjxP+k?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 2610c285-4e8e-48f4-80dd-08ddb5361664 X-MS-Exchange-CrossTenant-AuthSource: CH3PR12MB9194.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Jun 2025 04:50:06.7181 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: unBBOIG/ctRvFh6q8q2/rMm09W0Bt1IG5ALKEjDmCYBsMPV+9R9DfgMbRXDdfiBK2FCCbCLC1Zht1/p5/Q0TuA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ2PR12MB7990 On 25/6/25 00:10, Vishal Annapurve wrote: > On Tue, Jun 24, 2025 at 6:08 AM Jason Gunthorpe wrote: >> >> On Tue, Jun 24, 2025 at 06:23:54PM +1000, Alexey Kardashevskiy wrote: >> >>> Now, I am rebasing my RFC on top of this patchset and it fails in >>> kvm_gmem_has_safe_refcount() as IOMMU holds references to all these >>> folios in my RFC. >>> >>> So what is the expected sequence here? The userspace unmaps a DMA >>> page and maps it back right away, all from the userspace? The end >>> result will be the exactly same which seems useless. And IOMMU TLB > > As Jason described, ideally IOMMU just like KVM, should just: > 1) Directly rely on guest_memfd for pinning -> no page refcounts taken > by IOMMU stack > 2) Directly query pfns from guest_memfd for both shared/private ranges > 3) Implement an invalidation callback that guest_memfd can invoke on > conversions. > > Current flow: > Private to Shared conversion via kvm_gmem_convert_range() - > 1) guest_memfd invokes kvm_gmem_invalidate_begin() for the ranges > on each bound memslot overlapping with the range > -> KVM has the concept of invalidation_begin() and end(), > which effectively ensures that between these function calls, no new > EPT/NPT entries can be added for the range. > 2) guest_memfd invokes kvm_gmem_convert_should_proceed() which > actually unmaps the KVM SEPT/NPT entries. > 3) guest_memfd invokes kvm_gmem_execute_work() which updates the > shareability and then splits the folios if needed > > Shared to private conversion via kvm_gmem_convert_range() - > 1) guest_memfd invokes kvm_gmem_invalidate_begin() for the ranges > on each bound memslot overlapping with the range > 2) guest_memfd invokes kvm_gmem_convert_should_proceed() which > actually unmaps the host mappings which will unmap the KVM non-seucure > EPT/NPT entries. > 3) guest_memfd invokes kvm_gmem_execute_work() which updates the > shareability and then merges the folios if needed. > > ============================ > > For IOMMU, could something like below work? > > * A new UAPI to bind IOMMU FDs with guest_memfd ranges Done that. > * VFIO_DMA_MAP/UNMAP operations modified to directly fetch pfns from > guest_memfd ranges using kvm_gmem_get_pfn() This API imho should drop the confusing kvm_ prefix. > -> kvm invokes kvm_gmem_is_private() to check for the range > shareability, IOMMU could use the same or we could add an API in gmem > that takes in access type and checks the shareability before returning > the pfn. Right now I cutnpasted kvm_gmem_get_folio() (which essentially is filemap_lock_folio()/filemap_alloc_folio()/__filemap_add_folio()) to avoid new links between iommufd.ko and kvm.ko. It is probably unavoidable though. > * IOMMU stack exposes an invalidation callback that can be invoked by > guest_memfd. > > Private to Shared conversion via kvm_gmem_convert_range() - > 1) guest_memfd invokes kvm_gmem_invalidate_begin() for the ranges > on each bound memslot overlapping with the range > 2) guest_memfd invokes kvm_gmem_convert_should_proceed() which > actually unmaps the KVM SEPT/NPT entries. > -> guest_memfd invokes IOMMU invalidation callback to zap > the secure IOMMU entries. > 3) guest_memfd invokes kvm_gmem_execute_work() which updates the > shareability and then splits the folios if needed > 4) Userspace invokes IOMMU map operation to map the ranges in > non-secure IOMMU. > > Shared to private conversion via kvm_gmem_convert_range() - > 1) guest_memfd invokes kvm_gmem_invalidate_begin() for the ranges > on each bound memslot overlapping with the range > 2) guest_memfd invokes kvm_gmem_convert_should_proceed() which > actually unmaps the host mappings which will unmap the KVM non-seucure > EPT/NPT entries. > -> guest_memfd invokes IOMMU invalidation callback to zap the > non-secure IOMMU entries. > 3) guest_memfd invokes kvm_gmem_execute_work() which updates the > shareability and then merges the folios if needed. > 4) Userspace invokes IOMMU map operation to map the ranges in secure IOMMU. Alright (although this zap+map is not necessary on the AMD hw). > There should be a way to block external IOMMU pagetable updates while > guest_memfd is performing conversion e.g. something like > kvm_invalidate_begin()/end(). > >>> is going to be flushed on a page conversion anyway (the RMPUPDATE >>> instruction does that). All this is about AMD's x86 though. >> >> The iommu should not be using the VMA to manage the mapping. It should > > +1. Yeah, not doing this already, because I physically cannot map gmemfd's memory in IOMMU via VMA (which allocates memory via gup() so wrong memory is mapped in IOMMU). Thanks, >> be directly linked to the guestmemfd in some way that does not disturb >> its operations. I imagine there would be some kind of invalidation >> callback directly to the iommu. >> >> Presumably that invalidation call back can include a reason for the >> invalidation (addr change, shared/private conversion, etc) >> >> I'm not sure how we will figure out which case is which but guestmemfd >> should allow the iommu to plug in either invalidation scheme.. >> >> Probably invalidation should be a global to the FD thing, I imagine >> that once invalidation is established the iommu will not be >> incrementing page refcounts. > > +1. Alright. Thanks for the comments. > >> >> Jason -- Alexey