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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8395FC433FE for ; Thu, 27 Oct 2022 00:34:29 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F04198E0002; Wed, 26 Oct 2022 20:34:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E8CE18E0001; Wed, 26 Oct 2022 20:34:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CC1B68E0002; Wed, 26 Oct 2022 20:34:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id B502C8E0001 for ; Wed, 26 Oct 2022 20:34:28 -0400 (EDT) Received: from smtpin06.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 882C91608FE for ; Thu, 27 Oct 2022 00:34:28 +0000 (UTC) X-FDA: 80064858216.06.7E23884 Received: from mx0b-00069f02.pphosted.com (mx0b-00069f02.pphosted.com [205.220.177.32]) by imf24.hostedemail.com (Postfix) with ESMTP id 1656818003A for ; Thu, 27 Oct 2022 00:34:27 +0000 (UTC) Received: from pps.filterd (m0246630.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 29QMW9sn000954; Thu, 27 Oct 2022 00:34:15 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : content-type : in-reply-to : mime-version; s=corp-2022-7-12; bh=7CqWoGNPislws48PL2HBt8w5ENHgGzFukTXAc3siTu0=; b=LRx8825pLglYM6HOUsvmuQ20uJR6KadGUQ/zZSJ1NVt5rOTvIDHBemysYKFOC41ky4wM MW+b35b0VLxOQVXW1Nd8nENJ+N8coLx+LUK2nzibEWHe9QaxPpt2Bx/o+3dU4SQiNc2h mQObF9PjAtB9+qm7LdKDpJbJR2tf5gE3vrt03dRhpWn33/lDzjlxGWIiUm4dVzmaqode ta+4hFhY+P7d8D9ibU60Yr/CNQo2vnI6snRCxy+Q4tcvPwCeaByyk4qSUoT/63jvhj00 PvdbGdiqJh7Wu6MsUdT4ZNm53k2puDdQz8QFmPC31RqykwVRRFKsCB1oz87sj3EXUNjN 4w== Received: from phxpaimrmta03.imrmtpd1.prodappphxaev1.oraclevcn.com (phxpaimrmta03.appoci.oracle.com [138.1.37.129]) by mx0b-00069f02.pphosted.com (PPS) with ESMTPS id 3kfax7rk20-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 27 Oct 2022 00:34:15 +0000 Received: from pps.filterd (phxpaimrmta03.imrmtpd1.prodappphxaev1.oraclevcn.com [127.0.0.1]) by phxpaimrmta03.imrmtpd1.prodappphxaev1.oraclevcn.com (8.17.1.5/8.17.1.5) with ESMTP id 29QMBECB006561; Thu, 27 Oct 2022 00:34:14 GMT Received: from nam10-bn7-obe.outbound.protection.outlook.com (mail-bn7nam10lp2108.outbound.protection.outlook.com [104.47.70.108]) by phxpaimrmta03.imrmtpd1.prodappphxaev1.oraclevcn.com (PPS) with ESMTPS id 3kfaggex0v-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 27 Oct 2022 00:34:14 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=k12z/nWn846KEe98FUo0UZwRm5TJlPgbG38qkCVswVY33SGO+uHN5zeA0cucrFlcXjYgLn5ToUPJK7/wzuIbW/4q1pPIJcvEalZYKQIyV1w/qOw/JltxgaN7xsH0aMPv1oNwef+fA7BhP9fC8Mj+m3eI+TXEWnhsQGtMeBJ1EBYa6y5v1/m1FMPdFf7xXBY8nehkzTGsKl7ccAoSqlW2GbA5R/9Iq2xvLCoO2sJLhmyrRT6T66hZb86z9xG35WPDLR6WyRuabiAwPAwPrLE51rLP8a52ADI4FIMXfbFq7IWixfqw6MnujEp7I0YwZE0qt8hJ5wo+gxyKba3K6qvKkA== 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-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=7CqWoGNPislws48PL2HBt8w5ENHgGzFukTXAc3siTu0=; b=aoLf12g4Bm07zMjZkIRbZx4+GGeVHJi1iTAn02jkaY6bgIOS5/TvPu4gg/FWKnwGIGJLmuanB+/j/jKNuW1/zPRKcfetoSDAZAJH/3lY0a0kHBNo2bTwBK1thIbyK4bB3FTBQOBW4EfdNaWAoZtNaqdTXrTrtg3pDcABX3cciRLY2bxKrYqi2RUTP2r3jBlXgMVQBMRw+LhVSJGA4GLhO7YIGqbhD7m/aYnyV2CYYU1wVz3Tr+b2LxZ8IvzaZn5kEHkbUPJfog+aKLosVB/Y8JF6HbqMPoY6CLWoF1fSZtH5fNjUIbivj6Kczx4QeY4hKZB2aLLQUm+BVVxkldXybg== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=7CqWoGNPislws48PL2HBt8w5ENHgGzFukTXAc3siTu0=; b=HJNcM3VjGGKqa1Y/CsJyytxfOVEei4yG2CUAxvE3x1urBhY+xVdLThYWDxQsIN9p9UXzNfx7S/IMeduxpBGI6TLoDdwbXpfuTsFp2bkXJjsygTpd3YUPLEUo+n9l3f+oSIeGxIj3rPu1HVx5XAERMYz8z6hNGUlZkzT3x13gzvc= Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by BY5PR10MB4116.namprd10.prod.outlook.com (2603:10b6:a03:203::13) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5746.26; Thu, 27 Oct 2022 00:34:09 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::58e9:95ba:d31e:ddd3]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::58e9:95ba:d31e:ddd3%5]) with mapi id 15.20.5746.028; Thu, 27 Oct 2022 00:34:09 +0000 Date: Wed, 26 Oct 2022 17:34:04 -0700 From: Mike Kravetz To: Peter Xu Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-ia64@vger.kernel.org, Baolin Wang , David Hildenbrand , Christophe Leroy , "Aneesh Kumar K . V" , Naoya Horiguchi , Michael Ellerman , Muchun Song , Andrew Morton Subject: Re: [PATCH v3] hugetlb: simplify hugetlb handling in follow_page_mask Message-ID: References: <20220919021348.22151-1-mike.kravetz@oracle.com> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: MW4PR04CA0357.namprd04.prod.outlook.com (2603:10b6:303:8a::32) To BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY5PR10MB4196:EE_|BY5PR10MB4116:EE_ X-MS-Office365-Filtering-Correlation-Id: 832c52ac-7592-4121-1cbd-08dab7b2f670 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: +5lukjWAtfwuR8CW5OK6RhGzouwswCtewlDDpOcEvgs4qVIUS0cSfxWHuzhOX00DRtdqei+5PFotrYNzRHXYrNBXXhcGDxXi2oJwpi4o4bCFXxSycSmph9upG12NITRaLWe2NLe2oaSU4HUzFxBXsNDYn9ubOtoxM4AQwcGLI67E02VkMLKgck6SZswykizUvOGwO1PYBdOuAsmddzqGUXkz7gPJzjISQTtIsFcAaztKoRemTnIyjYwgu/EFI94tzsbRyWpZz4IinGSwH6FZC/HVmcIu7BZX8jiw2QX3buvw7aJ9fbpl6wo9IUW5jJ1EG0f/GBZY1stKTkbQhJKWoCgXGcigaLudflj/kPg7D/qWDJ5fgvIa21GERPRCoN3I3FWgasZ3vOG6WwzQYSZw2hGJVq650IBPS3rQJHoLBk1W4X9PCSZ5SpvMw0NqF5qAqmAZSLBPwLKxVxOb8KFQ9VT2Vjj3TpClPyHeLIz+gyQki6APA7jAKZOC5kBUynTJe61QuxJj9m/TQD3c6WB6RUlfolFBC+oesS/MB9pw24RJGPVdMSk4y5kM9POvy1M0Q/C+s1z9EZdGPYN7g87/mIVTZ8GeuVol7vv4KkKTdX9N5zomkDJIXwtAWo9x6oKgjwn5zKleWZyTL2k6gcibXHqEMUGpqpT0xBP/4AuGJEFuLm3Ego50r7KnKZgC4tQIFF3fLbepbOgq7LkxXVqjOw== X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BY5PR10MB4196.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230022)(7916004)(366004)(346002)(136003)(396003)(376002)(39860400002)(451199015)(186003)(66476007)(5660300002)(44832011)(66946007)(7416002)(8936002)(66556008)(83380400001)(38100700002)(86362001)(6916009)(54906003)(6486002)(26005)(6512007)(9686003)(478600001)(316002)(8676002)(4326008)(6506007)(33716001)(6666004)(53546011)(41300700001)(2906002);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?p8xszGyeESy7Ky18c5HASNoJiVm0Pb0REteQ51wudBZb+FRAf7T0bbBRcjAu?= =?us-ascii?Q?7G5PouugtGjfs82GdFEhsY3B6Ot642AwCO6wLiE6m6YvxZS/3g4ng398xczf?= =?us-ascii?Q?AV/HA4gstBuVwzUK1RwoxrXw6fhi4LV0Deu0NDT08xoyhT8uMyfH7zZe2Kmf?= =?us-ascii?Q?TWwlataIg+Bxu0gToNv801wd2C7TcXCpYIEi6XS6navAkR1nhk20yY7wPRQ8?= =?us-ascii?Q?zjVOO34vBIEuoGJwDs/qEO8NSJi74isIQjh7XqQFx9XMisiyPZ9n9vPLpSs4?= =?us-ascii?Q?C0+SASXLV+i1857X7kPjf0NiW6mUMmHC1yy3heEX4SaGaQZ4u1TLzPkSdxoD?= =?us-ascii?Q?EPGJv0v2kIaG8yeR1gHRsqa8uieNUy0GtOV/yuq6w9KALbDREbjpzx6vWYC5?= =?us-ascii?Q?HDu/VhhmxoJldHKPYaRstFUE7/t/2ipyQNrJqzmmXFfa6FC65PfGjl+00qVT?= =?us-ascii?Q?pWCJxfs01FYx05cViJIA6xfnUYmULIqMMF6yZgEh4G8XfOeQU/GnULDaa+Z+?= =?us-ascii?Q?/0iPG/cyMuHoRwHIi9UAdMVqH3mQHH4/cZ2Re2XvVSn/w8tdQjGyP5FpGkXG?= =?us-ascii?Q?4jqkzi3SEeKFJLDsQ5ZORxypR6Lah5nqLBHe+qJNEBOGfbfVW3ERrjFsVuN1?= =?us-ascii?Q?qWQYLHUs57u2qEuQ5LVGdD97vgcwed5asFw2NnolCibs9JMt81gq4MxyjofF?= =?us-ascii?Q?F12aZTP//CmjPt4XVo0+hlVUa1simY41lAPKAnPg5vsW9sfTYfZDVm4GsGca?= =?us-ascii?Q?nopkE7VrDwzdkNPac7yGLpJ/LaSEFhszHcCvIP+mg6kkt/50bKdJnbOJmLVf?= =?us-ascii?Q?SDtt66aFSIB1nBpjGmrmIc2as0CDzRTxmlQPQGqmJGmpT7mldvAtrCLywz5W?= =?us-ascii?Q?VS7sbBvULgATCZajvPoa9+CdRmpMI7HVq64FuovG1BFoUJOkZa0R0hjR7O0I?= =?us-ascii?Q?jqdVNIpHI6XdhTsyQ52aMwMoHWJ9GeUAsm1HDuuTwjO0J+yn2gKVbBS4U0sS?= =?us-ascii?Q?/vY3xzpyrlfE3KtjALXSezEsIy8BkCVXG6wyyk9Gw64zv8c6z5v+hRLjkSGQ?= =?us-ascii?Q?gysIMEHjKPOkZpk3pIF7GtXfZ4dbdgBerGa7jFW7pavhpnkrD18L8YkOFwfa?= =?us-ascii?Q?E8biWsulbkk+oy7xijHmjXKd1XcpYr/4hNRhX3oaOvFf3cmxL2kWxc/z7vGm?= =?us-ascii?Q?q/3ArvxUI459X23Cx/1xbS7oSJm8dkU9UsHHYMe4YiTNHLDa4EenXVkoCuVP?= =?us-ascii?Q?9dDwfkCdNyMecUJPaMAoIYRHcYVUdLATazYgYoFrI5Rxibd3fxtxLAChhEKU?= =?us-ascii?Q?Lht9uf0A8o1qEzx6zYENftSDhldndWu26N5VOIOANJy3+uRl9EYkVNcqC0kL?= =?us-ascii?Q?ge983kjF7DgSbwVtjZBHInSYB6Ja657svC0Mmql16mWg/JZvoMSu+phkT23u?= =?us-ascii?Q?VURDf7uBLVVNQhIUxmkfAEMItRwbF7Jj+/W1XRRLHGhE4bB0jnnyPHCG2cAx?= =?us-ascii?Q?MNqUMhVgQy4oKxIEbMisOgL3mU7jekPVyyK8SyeI/5hPvb0T6t0sd23DRP0/?= =?us-ascii?Q?RL0EsM13SouC4vnZeRd73oDa7lgzssTt9QvgSDuG0o+4A8zfULluQExEFvdS?= =?us-ascii?Q?Kw=3D=3D?= X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 832c52ac-7592-4121-1cbd-08dab7b2f670 X-MS-Exchange-CrossTenant-AuthSource: BY5PR10MB4196.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Oct 2022 00:34:09.5450 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: YmXoyEbRhaGCFAZOfMbYRA3lfGrdOGfnn75xL367JNk0w8HdqCA3Ls46TLxD2nm4axIEe/+6ac73ICm4XKq7lA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR10MB4116 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-10-26_10,2022-10-26_01,2022-06-22_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 spamscore=0 suspectscore=0 phishscore=0 adultscore=0 mlxscore=0 mlxlogscore=999 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2210170000 definitions=main-2210270001 X-Proofpoint-GUID: fw9fhbyyge4U_DqnXSqatBFQLaU4LiTn X-Proofpoint-ORIG-GUID: fw9fhbyyge4U_DqnXSqatBFQLaU4LiTn ARC-Seal: i=2; s=arc-20220608; d=hostedemail.com; t=1666830868; a=rsa-sha256; cv=pass; b=06RVVW6xAuad91YrdHhmvPyGJonhBuzNuyl91EyiYauA0VBOiQtJDZU3ojMsHj61BgIUu3 w/HRnPJBaHSnJHrSTR/OvzRmPm07RpCMiExH6zGgUYP/pMB2+HCjZawBJRznfIQDraMrOK c+ASwk1WKUqIshXehFi85lIdE+dCnpQ= ARC-Authentication-Results: i=2; imf24.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=LRx8825p; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=HJNcM3Vj; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf24.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1666830868; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=7CqWoGNPislws48PL2HBt8w5ENHgGzFukTXAc3siTu0=; b=LKKU3EqXDVHU2vHq7Sv7fX+17cYViuDKgXvR4HPQUYaQiX8HM9s/YfA5yuOdsahUgY8BDW bKvLhYfXBK04OUxbceFu2ifp5YN7wKXUbeszV8eqrx4OXr/UxgCklZ0OOith3UZAfwFWag DvVz2qBIrAPJHCsFMgHYXHZAQapLHu4= X-Stat-Signature: e6uio69pkg64acn8sosqsqhuy1rbswj6 X-Rspamd-Queue-Id: 1656818003A Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=LRx8825p; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=HJNcM3Vj; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf24.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1666830867-558474 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 10/26/22 17:59, Peter Xu wrote: > Hi, Mike, > > On Sun, Sep 18, 2022 at 07:13:48PM -0700, Mike Kravetz wrote: > > +struct page *hugetlb_follow_page_mask(struct vm_area_struct *vma, > > + unsigned long address, unsigned int flags) > > +{ > > + struct hstate *h = hstate_vma(vma); > > + struct mm_struct *mm = vma->vm_mm; > > + unsigned long haddr = address & huge_page_mask(h); > > + struct page *page = NULL; > > + spinlock_t *ptl; > > + pte_t *pte, entry; > > + > > + /* > > + * FOLL_PIN is not supported for follow_page(). Ordinary GUP goes via > > + * follow_hugetlb_page(). > > + */ > > + if (WARN_ON_ONCE(flags & FOLL_PIN)) > > + return NULL; > > + > > +retry: > > + /* > > + * vma lock prevents racing with another thread doing a pmd unshare. > > + * This keeps pte as returned by huge_pte_offset valid. > > + */ > > + hugetlb_vma_lock_read(vma); > > I'm not sure whether it's okay to take a rwsem here, as the code can be > called by e.g. FOLL_NOWAIT? I think you are right. This is possible even thought not called this way today, > I'm wondering whether it's fine to just drop this anyway, just always walk > it lockless. IIUC gup callers should be safe here because the worst case > is the caller will fetch a wrong page, but then it should be invalidated > very soon with mmu notifiers. One thing worth mention is that pmd unshare > should never free a pgtable page. You are correct in that pmd unshare will not directly free a pgtable page. However, I think a 'very worst case' race could be caused by two threads(1,2) in the same process A, and another process B. Processes A and B share a PMD. - Process A thread 1 gets a *ptep via huge_pte_offset and gets scheduled out. - Process A thread 2 calls mprotect to change protection and unshares the PMD shared with process B. - Process B then unmaps the PMD shared with process A and the PMD page gets deleted. - The *ptep in Process A thread 1 then points into a freed page. This is VERY unlikely, but I do think it is possible and is the reason I may be overcautious about protecting against races with pmd unshare. -- Mike Kravetz > > IIUC it's also the same as fast-gup - afaiu we don't take the read vma lock > in fast-gup too but I also think it's safe. But I hope I didn't miss > something. > > -- > Peter Xu >