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emacs 28.2 From: Alistair Popple To: Andrew Morton Cc: John Hubbard , linux-mm@kvack.org, Ralph Campbell , nouveau@lists.freedesktop.org, stable@vger.kernel.org Subject: Re: [PATCH] mm: Take a page reference when removing device exclusive entries Date: Wed, 29 Mar 2023 12:45:44 +1100 In-reply-to: <20230328125558.90cf40060e238b24add51d23@linux-foundation.org> Message-ID: <87lejgtjbh.fsf@nvidia.com> Content-Type: text/plain X-ClientProxiedBy: SYBPR01CA0040.ausprd01.prod.outlook.com (2603:10c6:10:4::28) To BYAPR12MB3176.namprd12.prod.outlook.com (2603:10b6:a03:134::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BYAPR12MB3176:EE_|SA1PR12MB8985:EE_ X-MS-Office365-Filtering-Correlation-Id: ce38889c-4249-4cc9-ebc3-08db2ff85164 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 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:BYAPR12MB3176.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230028)(4636009)(376002)(136003)(39860400002)(396003)(346002)(366004)(451199021)(2906002)(83380400001)(8936002)(26005)(5660300002)(54906003)(6506007)(6486002)(6666004)(36756003)(316002)(6512007)(478600001)(66476007)(2616005)(186003)(66946007)(38100700002)(66556008)(8676002)(4326008)(6916009)(41300700001)(86362001);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?t6bQE/WTNnomIkUcI6HM601pWRtYGIBraohs11a4s/3769PBLHsyXO0WFfa/?= =?us-ascii?Q?I352Zy3FPuYmMZCQnYS8PHkHl8q5hKdoxbwuw5a256Y86rNami2c/fQxR7w4?= =?us-ascii?Q?gi1K96xeJLoMlm3dYYqtI9RYhb46eb3Up8azEvIGwl+8ikb6N4zuGQvE8qa2?= =?us-ascii?Q?Bnp5M7N5f3rVfJRH8Dq2pqrWhmmr72jZzS49mBCfkvFR1rHZrPwWa8Y3cZ2L?= =?us-ascii?Q?C3/7nLOmpTeMlRIZw5t6lE19eNOUl/TuVOmMzSv8xUxkAfHrsnPll4wrO6zU?= =?us-ascii?Q?J64vJ1FU0auxE/3CarZQhzn+RldoS5zB+snD64v4NlMg3/zKwUiGUkqCqYlk?= =?us-ascii?Q?OFR63b+K3i8zEQKgSb8HivKo8ZZSVGMHcbxI/ZkMgjcfBy0XfafiH8hnSG8I?= =?us-ascii?Q?wc8ptdIFxnLDZCCtcwArUrgqREwovG3dVqz32B4dLuvpsehNKJxISoF36VGU?= =?us-ascii?Q?JeGtCJ04EEsCuZh6+iXyNgB1JkAFVK5EdQkmUHud4t0uT8uX/9J582o+T9re?= =?us-ascii?Q?Jsp43heGKZZvk77oelwxrV5LG5hDvqKM4kpDjeLgK2UkoWqzT6M3ljdmfogx?= =?us-ascii?Q?Oa6QaCE+O6+524p9bnk1biUoNJgF07zBmpxqQmbTyQki/JelAtwik9YY1sE3?= =?us-ascii?Q?3yQjywSLSUXJt50OFeJgWDTyMoktzXiiHcNk/kykhwMEauQsD+omYooXy2Jd?= =?us-ascii?Q?NDIrIQ9yEi87EZzhUNqHrmvMbnyh8NbSpOxHeCnburSnXfmbdbG9HKOC66gG?= =?us-ascii?Q?PBtwLlsKmqTYqA6xfo1ZwbZttV/hQvmcUukOWw/R4aPR3PkLs3Lb1zeBxtLY?= =?us-ascii?Q?bFuUDV8DpzUQKZBu2/1FKIeDvQd+gqhuB9azj4jqJRpuo93RQsD/X/E93NXT?= =?us-ascii?Q?d1yx0uQb+QkM5hov2fjMNR3w1VHXnfrw2yc7viAp4JhvUism3+Aa8CifzJYp?= =?us-ascii?Q?Eogx9BJmBA5A+LDJApcO60wP7aoVdquqAxMy66/fB9iGtW3ulNJbxJ5luoW1?= =?us-ascii?Q?7+2+n4GHfV7ypU/ySn5Sm2RV28zrqBDMZVEFvDSV3gYrXmD2JXgUD+HEYflt?= =?us-ascii?Q?IdS8LjS9Q3PtDZeeaV76WiuILOXeoJKGJQMBe0YG5ncAd9bEW00idEocuHFu?= =?us-ascii?Q?qq3M0JDEdp24vqlLeAAFq7RW7BiX/7x+bD2BH/20f7WS+itsfoUQ44wEv2Hq?= =?us-ascii?Q?gkpriuMwL4gWb0a/pfut5Gacc6GKUKNGrthGXVLVghjJxsFiRG5biIbdClyK?= =?us-ascii?Q?Ch2OoPzbalehFd3jecg5LXmIcA0n4iZKAZrGuMKRBn/Iw5aXi3pzwg9cAKaE?= =?us-ascii?Q?me3xQ0FCycZnz/2p2gKV7fzovuSBWkjLwbCRdRYqiFLnk/lNEG9Q+O0r96Ts?= =?us-ascii?Q?5ITzjbR6KaSWlOb18bFFIL8g/hWJKwyzS+ic65yIHZHuo3yGlY35gX3Anc/T?= =?us-ascii?Q?VQ7MJWWRtVzHHCXqQPz0G9w/GbGYXUIshbqzo+DEobvPBlK0s/301YvstgP/?= =?us-ascii?Q?7pndSaQRemfCPPig4HktfJrufRFO6/0U9RxjCf6fHyvnX7uIbq59WfGfXDmk?= =?us-ascii?Q?xItvh6mCbZjUHs7lVBTuooNRiE0cCtylQmQZ4w77?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ce38889c-4249-4cc9-ebc3-08db2ff85164 X-MS-Exchange-CrossTenant-AuthSource: BYAPR12MB3176.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Mar 2023 01:52:56.8753 (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: 7MKaEf/mYr6KFH+0APQOO4H5j648H3uCBYSbAd8vyJ0btqb8jGsDwtCs2u2YxAjYP/V5R9LQSekJ4cVlWA9LfQ== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA1PR12MB8985 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org John Hubbard writes: >> warnings such as PAGE_FLAGS_CHECK_AT_FREE due to the page being locked >> when the refcount drops to zero. Note that during removal of the >> device exclusive entry the PTE is currently re-checked under the PTL >> so no futher bad page accesses occur once it is locked. > > Maybe change that last sentence to something like this: > > "Fix this by taking a page reference before starting to remove a device > exclusive pte. This is done safely in a lock-free way by first getting a > reference via get_page_unless_zero(), and then re-checking after > acquiring the PTL, that the page is the correct one." > > ? > > ...well, maybe that's not all that much help. But it does at least > provide the traditional description of what the patch *does*, at > the end of the commit description. But please treat this as just > an optional suggestion. My wording was probably a little awkward. The intent was to point out the existing code subsequent to taking the page lock was already correct/safe. I figured the patch itself does a pretty good of describing the actual fix so am inclined to leave it. Andrew Morton writes: > On Mon, 27 Mar 2023 23:25:49 -0700 John Hubbard wrote: > >> On the patch process, I see that this applies to linux-stable's 6.1.y >> branch. I'd suggest two things: >> >> 1) Normally, what I've seen done is to post against either the current >> top of tree linux.git, or else against one of the mm-stable branches. >> And then after it's accepted, create a version for -stable. > > Yup. I had to jiggle the patch a bit because > mmu_notifier_range_init_owner()'s arguments have changed. Once this > hits mainline, the -stable maintainers will probably ask for a version > which suits the relevant kernel version(s). Thanks Andrew. That's my bad, I was developing on top of v6.1 and neglected to rebase. Happy to provide versions for -stable as required.