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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham 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 A1A31C04AB4 for ; Wed, 15 May 2019 01:56:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 74B8320862 for ; Wed, 15 May 2019 01:56:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726302AbfEOB4d (ORCPT ); Tue, 14 May 2019 21:56:33 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:35434 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726174AbfEOB4c (ORCPT ); Tue, 14 May 2019 21:56:32 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 60CE1374; Tue, 14 May 2019 18:56:32 -0700 (PDT) Received: from [10.163.1.137] (unknown [10.163.1.137]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6AED13F71E; Tue, 14 May 2019 18:56:23 -0700 (PDT) Subject: Re: [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump To: Mark Rutland Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org, catalin.marinas@arm.com, will.deacon@arm.com, mhocko@suse.com, mgorman@techsingularity.net, james.morse@arm.com, robin.murphy@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, osalvador@suse.de, david@redhat.com, cai@lca.pw, logang@deltatee.com, ira.weiny@intel.com References: <1557824407-19092-1-git-send-email-anshuman.khandual@arm.com> <1557824407-19092-3-git-send-email-anshuman.khandual@arm.com> <20190514154000.GA20935@lakrids.cambridge.arm.com> From: Anshuman Khandual Message-ID: <107ce10f-622c-7914-6269-cff5509b084f@arm.com> Date: Wed, 15 May 2019 07:26:32 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190514154000.GA20935@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/14/2019 09:10 PM, Mark Rutland wrote: > On Tue, May 14, 2019 at 02:30:05PM +0530, Anshuman Khandual wrote: >> The arm64 pagetable dump code can race with concurrent modification of the >> kernel page tables. When a leaf entries are modified concurrently, the dump >> code may log stale or inconsistent information for a VA range, but this is >> otherwise not harmful. >> >> When intermediate levels of table are freed, the dump code will continue to >> use memory which has been freed and potentially reallocated for another >> purpose. In such cases, the dump code may dereference bogus addressses, >> leading to a number of potential problems. >> >> Intermediate levels of table may by freed during memory hot-remove, or when >> installing a huge mapping in the vmalloc region. To avoid racing with these >> cases, take the memory hotplug lock when walking the kernel page table. >> >> Signed-off-by: Anshuman Khandual > Can we please move this after the next patch (which addresses the huge > vmap case), and change the last paragraph to: > > Intermediate levels of table may by freed during memory hot-remove, > which will be enabled by a subsequent patch. To avoid racing with > this, take the memory hotplug lock when walking the kernel page table. > > With that, this looks good to me. Sure will do.