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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 CD8C4C49ED7 for ; Tue, 17 Sep 2019 02:43:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A861520678 for ; Tue, 17 Sep 2019 02:43:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392007AbfIQCnd convert rfc822-to-8bit (ORCPT ); Mon, 16 Sep 2019 22:43:33 -0400 Received: from tyo161.gate.nec.co.jp ([114.179.232.161]:55623 "EHLO tyo161.gate.nec.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391292AbfIQCnb (ORCPT ); Mon, 16 Sep 2019 22:43:31 -0400 Received: from mailgate01.nec.co.jp ([114.179.233.122]) by tyo161.gate.nec.co.jp (8.15.1/8.15.1) with ESMTPS id x8H2h6li025318 (version=TLSv1.2 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Tue, 17 Sep 2019 11:43:06 +0900 Received: from mailsv01.nec.co.jp (mailgate-v.nec.co.jp [10.204.236.94]) by mailgate01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x8H2h6wQ022753; Tue, 17 Sep 2019 11:43:06 +0900 Received: from mail01b.kamome.nec.co.jp (mail01b.kamome.nec.co.jp [10.25.43.2]) by mailsv01.nec.co.jp (8.15.1/8.15.1) with ESMTP id x8H2eBCX014414; Tue, 17 Sep 2019 11:43:06 +0900 Received: from bpxc99gp.gisp.nec.co.jp ([10.38.151.147] [10.38.151.147]) by mail03.kamome.nec.co.jp with ESMTP id BT-MMP-1148208; Tue, 17 Sep 2019 11:34:44 +0900 Received: from BPXM20GP.gisp.nec.co.jp ([10.38.151.212]) by BPXC19GP.gisp.nec.co.jp ([10.38.151.147]) with mapi id 14.03.0439.000; Tue, 17 Sep 2019 11:34:43 +0900 From: Toshiki Fukasawa To: David Hildenbrand , "linux-mm@kvack.org" , "dan.j.williams@intel.com" CC: Toshiki Fukasawa , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" , "mhocko@kernel.org" , "adobriyan@gmail.com" , "hch@lst.de" , "longman@redhat.com" , "sfr@canb.auug.org.au" , "mst@redhat.com" , Naoya Horiguchi , Junichi Nomura Subject: Re: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver. Thread-Topic: [RFC PATCH v2] mm: initialize struct pages reserved by ZONE_DEVICE driver. Thread-Index: AQHVZIp2xk1cU6nEkk+ez7kL5reVFKcdvuyAgAAVnwCAAAk8gIAEZuMAgAAgogCADDvdgA== Date: Tue, 17 Sep 2019 02:34:43 +0000 Message-ID: <31fd3c86-5852-1863-93bd-8df9da9f95b4@vx.jp.nec.com> References: <20190906081027.15477-1-t-fukasawa@vx.jp.nec.com> <40a1ce2e-1384-b869-97d0-7195b5b47de0@redhat.com> <6a99e003-e1ab-b9e8-7b25-bc5605ab0eb2@vx.jp.nec.com> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: ja-JP X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.34.125.135] Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-TM-AS-MML: disable Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/09/09 16:46, David Hildenbrand wrote: > Let's take a step back here to understand the issues I am aware of. I > think we should solve this for good now: > > A PFN walker takes a look at a random PFN at a random point in time. It > finds a PFN with SECTION_MARKED_PRESENT && !SECTION_IS_ONLINE. The > options are: > > 1. It is buddy memory (add_memory()) that has not been online yet. The > memmap contains garbage. Don't access. > > 2. It is ZONE_DEVICE memory with a valid memmap. Access it. > > 3. It is ZONE_DEVICE memory with an invalid memmap, because the section > is only partially present: E.g., device starts at offset 64MB within a > section or the device ends at offset 64MB within a section. Don't access it. I don't agree with case #3. In the case, struct page area is not allocated on ZONE_DEVICE, but is allocated on system memory. So I think we can access the struct pages. What do you mean "invalid memmap"? > > 4. It is ZONE_DEVICE memory with an invalid memmap, because the memmap > was not initialized yet. memmap_init_zone_device() did not yet succeed > after dropping the mem_hotplug lock in mm/memremap.c. Don't access it. > > 5. It is reserved ZONE_DEVICE memory ("pages mapped, but reserved for > driver") with an invalid memmap. Don't access it. > > I can see that your patch tries to make #5 vanish by initializing the > memmap, fair enough. #3 and #4 can't be detected. The PFN walker could > still stumble over uninitialized memmaps. >