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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MSGID_FROM_MTA_HEADER,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19017C433B4 for ; Thu, 1 Apr 2021 00:49:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DB6E261073 for ; Thu, 1 Apr 2021 00:49:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232796AbhDAAsw (ORCPT ); Wed, 31 Mar 2021 20:48:52 -0400 Received: from mail-bn7nam10on2060.outbound.protection.outlook.com ([40.107.92.60]:40417 "EHLO NAM10-BN7-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229497AbhDAAsR (ORCPT ); Wed, 31 Mar 2021 20:48:17 -0400 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=dOTr05b4kS9A0kcDoqed+/fCoqVC/7877eugNT0137vw/iKaO7Hihv+xNIhneHeBbGddpGBspaqJJuafzRQyUajdpSt3lStiSW6iEHrpjLKBQPJu7KH29TPAuZKTSorf8pZwt8jhQ0PZCl/W/jjXTVzUNLKjJKvu39Oatkr2/Pg53oFIbKsZP5TCVA7wC2+p43AHc92y92Fn1fzME3/kFVKWzQttJwgnapHGHJl74ZWGWRqIsoShm7y50jwxuC3M0bdgtMIO7trMIcEl3UHJp9NOXgFivPPODDEioW3zsQx9iiUYhmyyFOlK2YyaKzoUUai45OUvACr0HvfY0SEjhQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Bz98JO7Rw9cgfIpVlh5EBQkXIWFdkRDK6RFd3k/v4Fc=; b=NjqeWkKf6bAmVyjtn0UmeRw2Y32IboQISCcKq+3uaKw6HFdE1B8nyXH9+M14bg4jgA7dzUtpNSM49Y4fWsBnmxpXdYbP9C47mv8N3AjIKltLtIMOKGCAERpTCn/YFTKdso+HdDyzNERh+T6zb5SiSiSdpmKtTRTUIqw9PFSnq13tbDNhjeGuvhKnpWEbOrqqS//AiuRXOzj19+f1ji2S53IwmTMsqhxIj9/gD7nvSVV7C08VFWEYrDGUag4/DMF9JmxWFqBpJqE98S7doIIKGa2F7IgJGLugtNs9ABygZcW98TjCD0qcBXvaj/GMqtSY/e8V75Wq3GZAswFk3WZgqQ== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=nvidia.com; dmarc=pass action=none header.from=nvidia.com; dkim=pass header.d=nvidia.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=Nvidia.com; s=selector2; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Bz98JO7Rw9cgfIpVlh5EBQkXIWFdkRDK6RFd3k/v4Fc=; b=i/174J+krKtdZVcmGrUluXy0yJX2y3PTX6HE2bdzRu7H6y/8u3NwJISPKwXhZnSt0Y8Qp2XXveU6tBQsCLPts3mxyaT4oEZd3elf+NsoFfnLG1JJ9eqm7WvFnA0EuOX0jEsLDwo71S/sWnQRxouCNI6orHQjmI4754q2TfMFSCtOrQr3C3srqLWSMHCNUgCskAqcLgLidiuSSLg3hAz5Mo43X9zSUL/1fOa+uPZktZotAQ90L9Jov3q27gT3VQcMaIggRUsSfOMk/QoRURAycM/by3x4+roHtyoB3JWU06njOfuXkDB1xTKbn68ODRSiyhP1/fO2kOaPuFf4WdtUDw== Authentication-Results: nvidia.com; dkim=none (message not signed) header.d=none;nvidia.com; dmarc=none action=none header.from=nvidia.com; Received: from DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) by DM6PR12MB4402.namprd12.prod.outlook.com (2603:10b6:5:2a5::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3999.27; Thu, 1 Apr 2021 00:48:15 +0000 Received: from DM6PR12MB3834.namprd12.prod.outlook.com ([fe80::1c62:7fa3:617b:ab87]) by DM6PR12MB3834.namprd12.prod.outlook.com ([fe80::1c62:7fa3:617b:ab87%6]) with mapi id 15.20.3999.028; Thu, 1 Apr 2021 00:48:15 +0000 Date: Wed, 31 Mar 2021 21:48:13 -0300 From: Jason Gunthorpe To: Alistair Popple Cc: linux-mm@kvack.org, nouveau@lists.freedesktop.org, bskeggs@redhat.com, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, dri-devel@lists.freedesktop.org, jhubbard@nvidia.com, rcampbell@nvidia.com, jglisse@redhat.com, hch@infradead.org, daniel@ffwll.ch, willy@infradead.org, Christoph Hellwig Subject: Re: [PATCH v7 5/8] mm: Device exclusive memory access Message-ID: <20210401004813.GT1463678@nvidia.com> References: <20210326000805.2518-1-apopple@nvidia.com> <2124945.3NMGunUBXV@nvdebian> <20210331134604.GK1463678@nvidia.com> <35941260.J9UuDlmC3F@nvdebian> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <35941260.J9UuDlmC3F@nvdebian> X-Originating-IP: [142.162.115.133] X-ClientProxiedBy: BL1PR13CA0035.namprd13.prod.outlook.com (2603:10b6:208:257::10) To DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (142.162.115.133) by BL1PR13CA0035.namprd13.prod.outlook.com (2603:10b6:208:257::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3999.16 via Frontend Transport; Thu, 1 Apr 2021 00:48:14 +0000 Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1lRlVN-006Z2B-Pv; Wed, 31 Mar 2021 21:48:13 -0300 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 42981125-12dd-49f0-5d63-08d8f4a7d566 X-MS-TrafficTypeDiagnostic: DM6PR12MB4402: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8273; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR12MB3834.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(4636009)(366004)(2616005)(2906002)(426003)(9786002)(6862004)(9746002)(6636002)(36756003)(7416002)(66946007)(86362001)(26005)(38100700001)(33656002)(66556008)(4326008)(8936002)(186003)(5660300002)(1076003)(8676002)(83380400001)(37006003)(66476007)(498600001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData: =?us-ascii?Q?lEx2oTexgFZdT3BrobyUhqtm8q8YzB2tW/kwCH7j2EgU23wShM61IuiqjU16?= =?us-ascii?Q?5sLkf8KUCGTVLsLFcNzIymHSaiyiwmf3zVQ99VQ/yWXd3yOm2cX+WapzDvcd?= =?us-ascii?Q?Z2H8IF7uXenpTdnCdpq1fXchC2QPR43Mzow0+7ZKEmVuQqh+LRxZPiKhfu2I?= =?us-ascii?Q?QH6/LIZ5O/nkCuh5/VctsKNdd9N1ufwG5A3UX4W38hEBMVQ3iRW//kqKA9xm?= =?us-ascii?Q?2/4mH+w0UWG5oF8NB3afwEsW2kdMVGg1N9M+ljdcw/K326p0XtrIE4/FWN9n?= =?us-ascii?Q?NAdN8Ro0Eu4DO7D+KCWK5R/Jwx5k4v9ETqY6+/X1W6fITcrGOO4UPQQrOSm6?= =?us-ascii?Q?7XOpRIMpw7rGM7eDGwSvm+AYwtbsOkxV8QEoZNN8SeAxe4bUee6b0F+Yydl/?= =?us-ascii?Q?Mbeh/ls6MVymOD7WeyZrKJgewaDQ8I15MMwllnJA2FytftBdi9hf1cQW/VDv?= =?us-ascii?Q?zkVebFBm15qlChPiMgQozv2vaCX0EhqAeS2y7fZONc8O7NhSuNqu0o3e7Njk?= =?us-ascii?Q?RQTd0cNGm+50le+bhoZI8OEVvGhH08wRPclwK9szGgpXHZCR4FVdWmx/s7dp?= =?us-ascii?Q?o/qPL/ke5mzM4rRFb6W8VjY49ByfmwS/5bPgw9XEYvcGmpG6rdNnSTapPMf0?= =?us-ascii?Q?XnFDF/JzR5emzmSMgv86PT4HtLFpkkpAUeE/X4yp1gI9SCfyNBgLInHanSvT?= =?us-ascii?Q?l22mi8QI/aDC/ROflHDhE5IYuG97j2SBWaY56Vk7TOZC9bcd6MFbi9g6+Zur?= =?us-ascii?Q?A4Bh01AS++kZHsrukbkwMLSUp8RR+4M7ET78A5nPJHiNp7dolvYscZCcESWM?= =?us-ascii?Q?JbF/t7AJOtlNGisN4LJsQMLOKhENXp1WVX7kYDhaGppH2kA3VpvFLY5cpCOG?= =?us-ascii?Q?yeAAEOs+f5jFYjwEkEnjOkmAyH3yaW45yADgSj43r7E/1nw/yvWZgQmdrrqm?= =?us-ascii?Q?vTxrf7LBPm9/FBwtwyLepUaKvHzHsAJPC20hnobtOyg9RcHO92PuKp4H4WXa?= =?us-ascii?Q?6p9K2KOsFffG22GtUCLCxVKbMEf3q1i8Jjb8ARjwde/JvIq9yzzcD3Gt7JHC?= =?us-ascii?Q?ADjYQCvLlzmL6vlaH10Fee5EqlDYYfqwETM0RKGGRVaxTSNpIcM1dq1L4JAI?= =?us-ascii?Q?SLIk4ic93TqRH+oRijXLHQUEJGRJs1+0GfVpVoYqjfk6CXfygYRZ4RPAKXUt?= =?us-ascii?Q?WZwcAOUOj/UjcBbZUM0Cy9iLHndJtwy/Z6aXeP5pNvD518MwUK9sVhdeHIwV?= =?us-ascii?Q?x5V1mCcCmM1z4c35QxRwcABm6FncycuxC9/vuiK9BW64oHXwRsrvBRWnJcPQ?= =?us-ascii?Q?fFpo/Cs2zXKODDLPsXFI5FNzNx/EM0w4hS7E7vNiLHudaQ=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 42981125-12dd-49f0-5d63-08d8f4a7d566 X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB3834.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Apr 2021 00:48:15.2764 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 9ddPwW3SODqDtjKE9BPzQsSDITial4Mn724XIUUoKzpSxwwY44v63KClh4EWpQ+M X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4402 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 01, 2021 at 11:45:57AM +1100, Alistair Popple wrote: > On Thursday, 1 April 2021 12:46:04 AM AEDT Jason Gunthorpe wrote: > > On Thu, Apr 01, 2021 at 12:27:52AM +1100, Alistair Popple wrote: > > > On Thursday, 1 April 2021 12:18:54 AM AEDT Jason Gunthorpe wrote: > > > > On Wed, Mar 31, 2021 at 11:59:28PM +1100, Alistair Popple wrote: > > > > > > > > > I guess that makes sense as the split could go either way at the > > > > > moment but I should add a check to make sure this isn't used with > > > > > pinned pages anyway. > > > > > > > > Is it possible to have a pinned page under one of these things? If I > > > > pin it before you migrate it then it remains pinned but hidden under > > > > the swap entry? > > > > > > At the moment yes. But I had planned (and this reminded me) to add a check > to > > > prevent marking pinned pages for exclusive access. > > > > How do you even do that without races with GUP fast? > > Unless I've missed something I think I've convinced myself it should be safe > to do the pin check after make_device_exclusive() has replaced all the PTEs > with exclusive entries. > > GUP fast sequence: > 1. Read PTE > 2. Pin page > 3. Check PTE > 4. if PTE changed -> unpin and fallback > > If make_device_exclusive() runs after (1) it will either succeed or see the > pin from (2) and fail (as desired). GUP should always see the PTE change and > fallback which will revoke the exclusive access. AFAICT the user can trigger fork at that instant and fork will try to copy the desposited migration entry before it has been checked Jason