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Fri, 29 Jul 2022 02:52:39 +0000 Received: from BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::eca6:a4a7:e2b2:27e7]) by BYAPR12MB3176.namprd12.prod.outlook.com ([fe80::eca6:a4a7:e2b2:27e7%5]) with mapi id 15.20.5458.024; Fri, 29 Jul 2022 02:52:38 +0000 References: <165490039431.944052.12458624139225785964.stgit@omen> <20220615155659.GA7684@nvidia.com> <20220623142139.462a0841.alex.williamson@redhat.com> <20220623204712.GG4147@nvidia.com> <87a6a2zyxk.fsf@nvdebian.thelocal> <20220624013415.GI4147@nvidia.com> <874k0ax1s0.fsf@nvdebian.thelocal> <878rodvcty.fsf@nvdebian.thelocal> <6492e852-8acf-95a9-a3a0-8ce8bbaf46d6@redhat.com> User-agent: mu4e 1.6.9; emacs 27.1 From: Alistair Popple To: David Hildenbrand Cc: Jason Gunthorpe , Alex Williamson , akpm@linux-foundation.org, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, paulmck@kernel.org, jhubbard@nvidia.com, joaodias@google.com Subject: Re: [PATCH] mm: Re-allow pinning of zero pfns Date: Fri, 29 Jul 2022 12:49:00 +1000 In-reply-to: <6492e852-8acf-95a9-a3a0-8ce8bbaf46d6@redhat.com> Message-ID: <87zggstyto.fsf@nvdebian.thelocal> Content-Type: text/plain X-ClientProxiedBy: BYAPR03CA0008.namprd03.prod.outlook.com (2603:10b6:a02:a8::21) To BYAPR12MB3176.namprd12.prod.outlook.com (2603:10b6:a03:134::26) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 4e90cc4d-ebc0-4b01-3347-08da710d659b X-MS-TrafficTypeDiagnostic: MN0PR12MB6077:EE_ X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=W3Eb+dKq; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf27.hostedemail.com: domain of apopple@nvidia.com designates 40.107.236.40 as permitted sender) smtp.mailfrom=apopple@nvidia.com; dmarc=pass (policy=reject) header.from=nvidia.com X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: s4dny5i5h7iadqmcfmpwhgtbufnuad7c X-Rspamd-Queue-Id: 4706A40017 X-HE-Tag: 1659063164-599932 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: David Hildenbrand writes: > On 28.07.22 10:45, Alistair Popple wrote: >> >> Looks like the original patch might need rebasing. I am about to post a >> clean-up for the tortured logic in check_and_migrate_movable_pages() so >> can incorporate it there, but I'm wondering what the consensus was for >> pinning of zero pfn? > > We have to keep it working right now, but in most cases (inside > MAP_PRIVATE regions) it's shaky and undesired. Ok. Well I've looked at this now so may as well stick Reviewed-by: Alistair Popple on it. However I think it needs rebasing, should I send an updated version? >> >> Currently my clean-up will result in PUP returning an error for the zero >> pfn rather than looping indefinitely in the kernel. However it wasn't >> clear from this thread if returning an error is ok, or if R/O pinning >> of the zero pfn should succeed? > > I'm working on proper COW breaking in MAP_PRIVATE mappings, which will, > for example, unshare the shared zeropage and properly replace it by > exclusive anon pages first in the FOLL_LONGTERM case.