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=-12.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 BBC72C4320A for ; Wed, 25 Aug 2021 18:47:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 924136109D for ; Wed, 25 Aug 2021 18:47:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240355AbhHYSsB (ORCPT ); Wed, 25 Aug 2021 14:48:01 -0400 Received: from mga14.intel.com ([192.55.52.115]:30027 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241704AbhHYSsA (ORCPT ); Wed, 25 Aug 2021 14:48:00 -0400 X-IronPort-AV: E=McAfee;i="6200,9189,10087"; a="217310518" X-IronPort-AV: E=Sophos;i="5.84,351,1620716400"; d="scan'208";a="217310518" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Aug 2021 11:47:14 -0700 X-IronPort-AV: E=Sophos;i="5.84,351,1620716400"; d="scan'208";a="444286725" Received: from cschaef-mobl1.amr.corp.intel.com (HELO [10.212.141.45]) ([10.212.141.45]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Aug 2021 11:47:13 -0700 Subject: Re: [PATCH v2] x86/mm: fix kern_addr_valid to cope with existing but not present entries To: Mike Rapoport , x86@kernel.org Cc: Andrew Morton , Andy Lutomirski , Dave Hansen , David Hildenbrand , Ingo Molnar , Jiri Olsa , Mike Rapoport , Oscar Salvador , Peter Zijlstra , Thomas Gleixner , Borislav Petkov , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org References: <20210819132717.19358-1-rppt@kernel.org> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210819132717.19358-1-rppt@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 8/19/21 6:27 AM, Mike Rapoport wrote: > Such PMDs are created when free_kernel_image_pages() frees regions larger > than 2Mb. In this case a part of the freed memory is mapped with PMDs and > the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will > mark the PMD as not present rather than wipe it completely. > > Make kern_addr_valid() to check whether higher level page table entries are > present before trying to dereference them to fix this issue and to avoid > similar issues in the future. > > Reported-by: Jiri Olsa > Signed-off-by: Mike Rapoport > Cc: # 4.4... > pmd = pmd_offset(pud, addr); > - if (pmd_none(*pmd)) > + if (!pmd_present(*pmd)) > return 0; Yeah, that seems like the right fix. The one kern_addr_valid() user is going to touch the memory so it *better* be present. p*d_none() was definitely the wrong check. Acked-by: Dave Hansen