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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 1BBF1C072B5 for ; Fri, 24 May 2019 04:53:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8C65217D7 for ; Fri, 24 May 2019 04:53:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731717AbfEXEwP (ORCPT ); Fri, 24 May 2019 00:52:15 -0400 Received: from foss.arm.com ([217.140.101.70]:33468 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726034AbfEXEwO (ORCPT ); Fri, 24 May 2019 00:52:14 -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 1D285374; Thu, 23 May 2019 21:52:14 -0700 (PDT) Received: from [10.162.42.134] (p8cg001049571a15.blr.arm.com [10.162.42.134]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 1D2773F703; Thu, 23 May 2019 21:52:07 -0700 (PDT) Subject: Re: [PATCH V4 3/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump To: Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org, catalin.marinas@arm.com, will.deacon@arm.com, mark.rutland@arm.com, ira.weiny@intel.com, david@redhat.com, cai@lca.pw, logang@deltatee.com, james.morse@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, dan.j.williams@intel.com, mgorman@techsingularity.net, osalvador@suse.de, ard.biesheuvel@arm.com References: <1558329516-10445-1-git-send-email-anshuman.khandual@arm.com> <1558329516-10445-4-git-send-email-anshuman.khandual@arm.com> <20190521101457.GK32329@dhcp22.suse.cz> From: Anshuman Khandual Message-ID: <4a9e0e2a-2acd-11b5-5181-41801cd11d98@arm.com> Date: Fri, 24 May 2019 10:22:18 +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: <20190521101457.GK32329@dhcp22.suse.cz> 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 05/21/2019 03:44 PM, Michal Hocko wrote: > On Mon 20-05-19 10:48:35, Anshuman Khandual wrote: >> The arm64 page table 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 addresses, >> leading to a number of potential problems. >> >> 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. > > I've had a comment on this patch in the previous version which didn't > get answered completely AFAICS. If you really insist then please make > sure to describe why does this really matter because this will make > any further changes to the hotplug locking harder and I would to see > that it is worth the additional trouble. Hello Michal, I was under the impression (seems wrongful now) that the previous discussion was complete. Nonetheless we can still discuss it further. Mark has responded on the previous V3 thread [1] and because this particular patch does not have any changes from last time, we can continue discussing this in that thread. [1] https://lkml.org/lkml/2019/5/22/613 - Anshuman