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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,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 7400BC04AB4 for ; Tue, 14 May 2019 15:40:24 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 438282086A for ; Tue, 14 May 2019 15:40:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fp4h1AQO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 438282086A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=6eTqnu8OCDn2mJ6t7yuuLphEakt8YVCHjR/gNraHpGE=; b=fp4h1AQOVR8jZN M4X6S1KpMVA0ec+40PkIDWHrj+AbWhgeCxxTgEx5ekGdLKzBWD4NwaSCebnOC3x/tQ1/BLT2wBvNC sy+HAzNIAQnyjyVih4+CSK4Ae00DWIVXtcwI8XeFb9HQLu2bdt4HMcGaq2rK76tan5f4zm0c+BHZL bXLgUYhGu5+wmYWKstB5IcDO8noK95j128reJ4y32B7+1vHymAfscMJRQcUxXEyUP3ab5tOnpAoJS Lqf0ivIbPGuWR/b8n1bAA4dXhmGC7+Sf1txmozq5nE2Bo//Ke3Yz327IvfDmowzqYXgUBnV0si1J0 tVwe0bCVV6/hwdU6rd5g==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hQZXN-0007nP-2V; Tue, 14 May 2019 15:40:17 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hQZXK-0007mV-A1 for linux-arm-kernel@lists.infradead.org; Tue, 14 May 2019 15:40:15 +0000 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 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-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) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190514_084014_357278_D1324E2C X-CRM114-Status: GOOD ( 19.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: cai@lca.pw, mhocko@suse.com, ira.weiny@intel.com, david@redhat.com, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, logang@deltatee.com, james.morse@arm.com, cpandya@codeaurora.org, arunks@codeaurora.org, akpm@linux-foundation.org, osalvador@suse.de, mgorman@techsingularity.net, dan.j.williams@intel.com, linux-arm-kernel@lists.infradead.org, robin.murphy@arm.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.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 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel