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 4F1B8C2D0A3 for ; Thu, 29 Oct 2020 08:16:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A441D2071A for ; Thu, 29 Oct 2020 08:16:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FzwQIOYu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A441D2071A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id E80B56B0075; Thu, 29 Oct 2020 04:16:09 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id E085E6B0078; Thu, 29 Oct 2020 04:16:09 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CF7836B007B; Thu, 29 Oct 2020 04:16:09 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0149.hostedemail.com [216.40.44.149]) by kanga.kvack.org (Postfix) with ESMTP id 9910D6B0075 for ; Thu, 29 Oct 2020 04:16:09 -0400 (EDT) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 39E003620 for ; Thu, 29 Oct 2020 08:16:09 +0000 (UTC) X-FDA: 77424255258.21.rice59_2f10d882728b Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 1E6CE180442C2 for ; Thu, 29 Oct 2020 08:16:09 +0000 (UTC) X-HE-Tag: rice59_2f10d882728b X-Filterd-Recvd-Size: 4941 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) by imf19.hostedemail.com (Postfix) with ESMTP for ; Thu, 29 Oct 2020 08:16:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1603959368; 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=FzwQIOYuQiYs8AOF0jSWfKko4kM786oPEch3YBrlcCg33I3RWV/PZlhcWMBvasAKZSkQo1 UuhP3NJLwgXzCgQEtlOh5mPQq4rCYOYgBbezoY3+SbQWYchutULQci4oL/QzuQ14pQ8ItF 9+GZvbOb12lYwWmjY/pkzovIBd1ffUE= 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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