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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 CDFA2C04AB4 for ; Tue, 14 May 2019 15:40:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAEAE20879 for ; Tue, 14 May 2019 15:40:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726201AbfENPkK (ORCPT ); Tue, 14 May 2019 11:40:10 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:57836 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725854AbfENPkK (ORCPT ); Tue, 14 May 2019 11:40:10 -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 73C8C374; Tue, 14 May 2019 08:40:09 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B89C3F703; Tue, 14 May 2019 08:40:06 -0700 (PDT) Date: Tue, 14 May 2019 16:40:00 +0100 From: Mark Rutland To: Anshuman Khandual 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 Subject: Re: [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Message-ID: <20190514154000.GA20935@lakrids.cambridge.arm.com> References: <1557824407-19092-1-git-send-email-anshuman.khandual@arm.com> <1557824407-19092-3-git-send-email-anshuman.khandual@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1557824407-19092-3-git-send-email-anshuman.khandual@arm.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Thanks, Mark. > --- > arch/arm64/mm/ptdump_debugfs.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/arm64/mm/ptdump_debugfs.c b/arch/arm64/mm/ptdump_debugfs.c > index 064163f..80171d1 100644 > --- a/arch/arm64/mm/ptdump_debugfs.c > +++ b/arch/arm64/mm/ptdump_debugfs.c > @@ -7,7 +7,10 @@ > static int ptdump_show(struct seq_file *m, void *v) > { > struct ptdump_info *info = m->private; > + > + get_online_mems(); > ptdump_walk_pgd(m, info); > + put_online_mems(); > return 0; > } > DEFINE_SHOW_ATTRIBUTE(ptdump); > -- > 2.7.4 >