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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A5000C4360C for ; Fri, 27 Sep 2019 19:34:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 516EB20872 for ; Fri, 27 Sep 2019 19:34:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="cjlFoayf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 516EB20872 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E2CFF8E0006; Fri, 27 Sep 2019 15:34:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E079E8E0001; Fri, 27 Sep 2019 15:34:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D1C308E0006; Fri, 27 Sep 2019 15:34:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0250.hostedemail.com [216.40.44.250]) by kanga.kvack.org (Postfix) with ESMTP id AF5088E0001 for ; Fri, 27 Sep 2019 15:34:04 -0400 (EDT) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id 3F5E88122 for ; Fri, 27 Sep 2019 19:34:04 +0000 (UTC) X-FDA: 75981701208.03.fire45_7a9382c369425 X-HE-Tag: fire45_7a9382c369425 X-Filterd-Recvd-Size: 7299 Received: from hqemgate14.nvidia.com (hqemgate14.nvidia.com [216.228.121.143]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Fri, 27 Sep 2019 19:34:02 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate14.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Fri, 27 Sep 2019 12:34:03 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Fri, 27 Sep 2019 12:34:00 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Fri, 27 Sep 2019 12:34:00 -0700 Received: from DRHQMAIL107.nvidia.com (10.27.9.16) by HQMAIL105.nvidia.com (172.20.187.12) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 27 Sep 2019 19:34:00 +0000 Received: from [10.2.173.141] (10.124.1.5) by DRHQMAIL107.nvidia.com (10.27.9.16) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Fri, 27 Sep 2019 19:33:59 +0000 Subject: Re: [PATCH v3 3/4] mm: don't expose non-hugetlb page to fast gup prematurely To: Michal Hocko CC: "Kirill A. Shutemov" , Yu Zhao , Peter Zijlstra , Andrew Morton , "Kirill A . Shutemov" , Ingo Molnar , "Arnaldo Carvalho de Melo" , Alexander Shishkin , Jiri Olsa , "Namhyung Kim" , Vlastimil Babka , Hugh Dickins , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Andrea Arcangeli , "Aneesh Kumar K . V" , David Rientjes , "Matthew Wilcox" , Lance Roy , Ralph Campbell , Jason Gunthorpe , Dave Airlie , Thomas Hellstrom , "Souptick Joarder" , Mel Gorman , Jan Kara , Mike Kravetz , Huang Ying , Aaron Lu , Omar Sandoval , Thomas Gleixner , "Vineeth Remanan Pillai" , Daniel Jordan , Mike Rapoport , "Joel Fernandes" , Mark Rutland , Alexander Duyck , Pavel Tatashin , David Hildenbrand , "Juergen Gross" , Anthony Yznaga , "Johannes Weiner" , "Darrick J . Wong" , , References: <20190914070518.112954-1-yuzhao@google.com> <20190924232459.214097-1-yuzhao@google.com> <20190924232459.214097-3-yuzhao@google.com> <20190925082530.GD4536@hirez.programming.kicks-ass.net> <20190925222654.GA180125@google.com> <20190926102036.od2wamdx2s7uznvq@box> <9465df76-0229-1b44-5646-5cced1bc1718@nvidia.com> <20190927123056.GE26848@dhcp22.suse.cz> From: John Hubbard X-Nvconfidentiality: public Message-ID: Date: Fri, 27 Sep 2019 12:31:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190927123056.GE26848@dhcp22.suse.cz> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1569612843; bh=MeghJIWhkw0Arc2Ircowp2EMbHoWiAASi13qzbI3yY4=; h=X-PGP-Universal:Subject:To:CC:References:From:X-Nvconfidentiality: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=cjlFoayf8XNNXIt628PYj0xOyaij2HU1GnckLi+EQWeuy9TRd6edAcZtTBQbWBlry 3AZ9q0zJrfTgRd5jIuJ3OSVLLQBYkm/Max7eF9lIihhZNuit3LHsqJd79ag7eL56AE 8Y0iNoZlHATjWXjtjavpJ0d4iBMBg6iGxc0LgNhBTIuyhTpuO2ChvN5ZLSrFULZ5jk ASMefF9L9DeEiKK6c5qP665RUptT45FFe752/ontq8xScLQ494AWpQ6kOLNpBnL9Vn TPUelg1EqiDG+i7wGPMXqcU4/jCYncI2badkj545jzn3eDVKywknDB6cUjz0n9D2Jk O+coMfKj0/HSQ== 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 9/27/19 5:33 AM, Michal Hocko wrote: > On Thu 26-09-19 20:26:46, John Hubbard wrote: >> On 9/26/19 3:20 AM, Kirill A. Shutemov wrote: >>> BTW, have you looked at other levels of page table hierarchy. Do we have >>> the same issue for PMD/PUD/... pages? >>> >> >> Along the lines of "what other memory barriers might be missing for >> get_user_pages_fast(), I'm also concerned that the synchronization between >> get_user_pages_fast() and freeing the page tables might be technically broken, >> due to missing memory barriers on the get_user_pages_fast() side. Details: >> >> gup_fast() disables interrupts, but I think it also needs some sort of >> memory barrier(s), in order to prevent reads of the page table (gup_pgd_range, >> etc) from speculatively happening before the interrupts are disabled. > > Could you be more specific about the race scenario please? I thought > that the unmap path will be serialized by the pte lock. > I don't see a pte lock anywhere here. This case is really pretty far out there, but without run-time memory barriers I don't think we can completely rule it out: CPU 0 CPU 1 -------- --------------- get_user_pages_fast() do_unmap() unmap_region() free_pgtables() /* * speculative reads, re-ordered * by the CPU at run time, not * compile time. The function calls * are not really in this order, but * the corresponding reads could be. */ gup_pgd_range() gup_p4d_range() gup_pud_range() gup_pmd_range() pmd = READ_ONCE(*pmdp) /* This is stale */ tlb_finish_mmu() tlb_flush_mmu() tlb_flush_mmu_tlbonly() tlb_flush() flush_tlb_mm flush_tlb_mm_range flush_tlb_others native_flush_tlb_others smp_call_function_many: IPIs ...blocks until CPU1 reenables interrupts local_irq_disable() ...continue the page walk based on stale/freed data... thanks, -- John Hubbard NVIDIA