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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 7DE2EC43334 for ; Wed, 5 Sep 2018 08:15:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 42AD02077C for ; Wed, 5 Sep 2018 08:15:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 42AD02077C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727865AbeIEMoj (ORCPT ); Wed, 5 Sep 2018 08:44:39 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:36634 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726342AbeIEMoj (ORCPT ); Wed, 5 Sep 2018 08:44:39 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5C79C40255C9; Wed, 5 Sep 2018 08:15:35 +0000 (UTC) Received: from localhost (ovpn-8-26.pek2.redhat.com [10.72.8.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7C85410075C9; Wed, 5 Sep 2018 08:15:34 +0000 (UTC) Date: Wed, 5 Sep 2018 16:15:31 +0800 From: Baoquan He To: "Kirill A. Shutemov" Cc: tglx@linutronix.de, mingo@kernel.org, hpa@zytor.com, thgarnie@google.com, kirill.shutemov@linux.intel.com, x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] x86/mm/KASLR: Adjust the vmemmap size according to paging mode Message-ID: <20180905081531.GN1740@192.168.1.3> References: <20180829021754.21850-1-bhe@redhat.com> <20180829021754.21850-2-bhe@redhat.com> <20180829120530.6dhgsautjjrj4ztt@kshutemo-mobl1> <20180830152512.GE14702@192.168.1.2> <20180902205242.kcpt6wsatacahswp@kshutemo-mobl1> <20180903074718.GD1740@192.168.1.3> <20180903102642.rmzawwqsqjvh2mkb@kshutemo-mobl1> <20180903145213.GG1740@192.168.1.3> <20180904081314.gdhm55qchhl5irmv@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180904081314.gdhm55qchhl5irmv@kshutemo-mobl1> User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Wed, 05 Sep 2018 08:15:35 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Wed, 05 Sep 2018 08:15:35 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'bhe@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/04/18 at 11:13am, Kirill A. Shutemov wrote: > On Mon, Sep 03, 2018 at 10:52:13PM +0800, Baoquan He wrote: > > On 09/03/18 at 01:26pm, Kirill A. Shutemov wrote: > > > > > But there's corner case when struct page is unreasonably large and > > > > > vmemmap_size will be way to large. We probably have to report an error if > > > > > we cannot fit vmemmap properly into virtual memory layout. > > > > > > > > Hmm, sizeof(struct page) can't exceed one whole page surely, otherwise > > > > system bootup can't go over vmemmap initlization. Except of this, we may > > > > need think about the virtual memory layout which vmemmap can be allowed > > > > to occupy. > > > > > > > > If KASAN enabled, KASLR disabled, > > > > 4-level 1TB + 1TB hole (2TB) > > > > 5-level 512TB + 2034TB hole (2.5PB) > > > > > > > > If KASAN disabled, KASLR enabled, > > > > 4-level 1TB + 1TB hole + 16TB (18TB) > > > > 5-level 512TB + 2034TB hole + 8PB (10.5PB) > > > > > > > > So, as you can see, if add check in memory KASLR code, we should only > > > > consider KASLR enabled case. We possibly don't need to worry about > > > > 5-level case since the size 10.5PB is even bigger than the maximum > > > > physical RAM mapping size. For 4-level, 18TB align to multiples of 2, it > > > > will be 32 times of the current 1TB, then we usually assume 64 as the > > > > default value of sizeof(struct page), then 64*32 == 1024. So we can add ~~~64*32 = 2048 Sorry, I made mistake here. > > > > check like this, what do you think? Or any other idea? > > > > > > Looks reasonable to me. > > > > > > But I would have the BUILD_BUG_ON() in generic code. If you struct page is > > > more than 1/4 of PAGE_SIZE something is horribly broken. > > > > Just the 1/4 of PAGE_SIZE is based on analysis of KASLR case. If > > non-KASLR case, it may not be that value. > > Even if it technically possible to have struct page larger than > PAGE_SIZE/4, it's just insane. > > > Not sure if it's OK to put it in generic code, and haven't thought of a > > good place, maybe in setup_arch(), just at the beginning? > > I don't see an obvious place too. Maybe free_area_init_nodes()? OK, you mean a more generic place, I only considered generic place in x86. The thing is not all ARCH-es set PAGE_SIZE as 4KB, e.g power and arm64 can have PAGE_SIZE of 64KB. For them, PAGE_SIZE/4, namely 16KB, is hardly reached. So my thought is either taking PAGE_SIZE/4 in x86 arch only, or using SZ_1K in free_area_init_nodes() as you suggested. What do you think? Thanks Baoquan