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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 280BAC55178 for ; Thu, 29 Oct 2020 08:16:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B981120720 for ; Thu, 29 Oct 2020 08:16:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ay06rFUM" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728742AbgJ2IQQ (ORCPT ); Thu, 29 Oct 2020 04:16:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:22417 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728550AbgJ2IQJ (ORCPT ); Thu, 29 Oct 2020 04:16:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603959367; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2gRwEwp+09CxPY3cDDGs5AqZnz2L4R+qK1xrKBZP/ZQ=; b=ay06rFUMq495NziQvvXEmjfl27QqLzDhX+fa4jGpMV7iYUr5G+e63O1tBDFA9Ul5oLop5C a8/TWffcMSMt6xjNKzy/qVY40B4oOUr4YUDs597pgypjwNsoZinHd7ELIVZ9qacTMV1TPn dllYntmtt8eAzvq8drrXaCf8X0MpNOc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-521-GwWoSv2-OMqDqihE-45P3g-1; Thu, 29 Oct 2020 04:16:02 -0400 X-MC-Unique: GwWoSv2-OMqDqihE-45P3g-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 5ED20809DC9; Thu, 29 Oct 2020 08:15:57 +0000 (UTC) Received: from [10.36.112.181] (ovpn-112-181.ams2.redhat.com [10.36.112.181]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3EBE05D9CC; Thu, 29 Oct 2020 08:15:48 +0000 (UTC) Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation To: Mike Rapoport , Andrew Morton Cc: Albert Ou , Andy Lutomirski , Benjamin Herrenschmidt , Borislav Petkov , Catalin Marinas , Christian Borntraeger , Christoph Lameter , "David S. Miller" , Dave Hansen , David Rientjes , "Edgecombe, Rick P" , "H. Peter Anvin" , Heiko Carstens , Ingo Molnar , Joonsoo Kim , "Kirill A. Shutemov" , Len Brown , Michael Ellerman , Mike Rapoport , Palmer Dabbelt , Paul Mackerras , Paul Walmsley , Pavel Machek , Pekka Enberg , Peter Zijlstra , "Rafael J. Wysocki" , Thomas Gleixner , Vasily Gorbik , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-pm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, sparclinux@vger.kernel.org, x86@kernel.org References: <20201025101555.3057-1-rppt@kernel.org> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <30075bb8-caed-c4de-c09e-e0f6fb964a8d@redhat.com> Date: Thu, 29 Oct 2020 09:15:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201025101555.3057-1-rppt@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.10.20 11:15, Mike Rapoport wrote: > From: Mike Rapoport > > Hi, > > During recent discussion about KVM protected memory, David raised a concern > about usage of __kernel_map_pages() outside of DEBUG_PAGEALLOC scope [1]. > > Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP it is > possible that __kernel_map_pages() would fail, but since this function is > void, the failure will go unnoticed. > > Moreover, there's lack of consistency of __kernel_map_pages() semantics > across architectures as some guard this function with > #ifdef DEBUG_PAGEALLOC, some refuse to update the direct map if page > allocation debugging is disabled at run time and some allow modifying the > direct map regardless of DEBUG_PAGEALLOC settings. > > This set straightens this out by restoring dependency of > __kernel_map_pages() on DEBUG_PAGEALLOC and updating the call sites > accordingly. > So, I was primarily wondering if we really have to touch direct mappings in hibernation code, or if we can avoid doing that. I was wondering if we cannot simply do something like kmap() when trying to access a !mapped page. Similar to reading old-os memory after kexec when in kdump. Just a thought. -- Thanks, David / dhildenb