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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,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 214BAC04E53 for ; Wed, 15 May 2019 16:59:00 +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 E924A20862 for ; Wed, 15 May 2019 16:58:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Uaq+SheW" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E924A20862 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=4+y3Oc6awkUxROX+BRGgxkfyZpjBLge332YSU3cfqxQ=; b=Uaq+SheWnyiYS4 VlAbTBcZKLUPmwZbV/onPZXO2O/fqAcQ87IEpZTM2M9lg3RaGJcIdCMlze8gJHgNiQJ33+4eeznzt g9+ZR08q06AuJfGW9K7EjMfe0aHT9i8FrnXlayb5TmLU05fyPl8pAXHKkihJ2hWTGlFekOrD0kzjf CQwK4ON70FWBSTp5SFjuqrz6nhwoOzTiG6+N7UdQDkbwhyQ5jGXPKTcMpTIDG65pDTSP6PARyrGJP /mUdbj49vlK0elK88Dh+iNqT1iaULC0OdCPEen639hiOID8KKHrmxXAh3zF4tRB195rPd21D+r5T5 DKVc1xuFzJXAmsTNkn1Q==; 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 1hQxF1-0006Ie-Fk; Wed, 15 May 2019 16:58:55 +0000 Received: from mx2.suse.de ([195.135.220.15] helo=mx1.suse.de) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1hQxEx-0006Hr-Kp for linux-arm-kernel@lists.infradead.org; Wed, 15 May 2019 16:58:53 +0000 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id CCF40ADAB; Wed, 15 May 2019 16:58:48 +0000 (UTC) Date: Wed, 15 May 2019 18:58:47 +0200 From: Michal Hocko To: Anshuman Khandual Subject: Re: [PATCH V3 2/4] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Message-ID: <20190515165847.GH16651@dhcp22.suse.cz> 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/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190515_095851_830914_9E751F8F X-CRM114-Status: GOOD ( 12.21 ) 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: mark.rutland@arm.com, ira.weiny@intel.com, david@redhat.com, catalin.marinas@arm.com, cai@lca.pw, 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 14-05-19 14:30:05, 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. Why is this a problem only on arm64 and why do we even care for debugfs? Does anybody rely on this thing to be reliable? Do we even need it? Who is using the file? I am asking because I would really love to make mem hotplug locking less scattered outside of the core MM than more. Most users simply shouldn't care. Pfn walkers should rely on pfn_to_online_page. -- Michal Hocko SUSE Labs _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel