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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0BB45C433FF for ; Wed, 7 Aug 2019 03:00:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD794216F4 for ; Wed, 7 Aug 2019 03:00:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727868AbfHGDAx (ORCPT ); Tue, 6 Aug 2019 23:00:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50500 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726334AbfHGDAx (ORCPT ); Tue, 6 Aug 2019 23:00:53 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 533A72F3677; Wed, 7 Aug 2019 03:00:52 +0000 (UTC) Received: from dhcp-128-65.nay.redhat.com (ovpn-12-17.pek2.redhat.com [10.72.12.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4CE575D6D0; Wed, 7 Aug 2019 03:00:45 +0000 (UTC) Date: Wed, 7 Aug 2019 11:00:41 +0800 From: Dave Young To: Pingfan Liu Cc: Thomas Gleixner , Andy Lutomirski , x86@kernel.org, Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , Dave Hansen , Peter Zijlstra , Masami Hiramatsu , Qian Cai , Vlastimil Babka , Daniel Drake , Jacob Pan , Michal Hocko , Eric Biederman , linux-kernel@vger.kernel.org, Baoquan He , kexec@lists.infradead.org, tony.luck@intel.com, Xunlei Pang Subject: Re: [PATCH 0/4] x86/mce: protect nr_cpus from rebooting by broadcast mce Message-ID: <20190807025843.GA4776@dhcp-128-65.nay.redhat.com> References: <1564995539-29609-1-git-send-email-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1564995539-29609-1-git-send-email-kernelfans@gmail.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Wed, 07 Aug 2019 03:00:52 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add Tony and Xunlei in cc. On 08/05/19 at 04:58pm, Pingfan Liu wrote: > This series include two related groups: > [1-3/4]: protect nr_cpus from rebooting by broadcast mce > [4/4]: improve "kexec -l" robustness against broadcast mce > > When I tried to fix [1], Thomas raised concern about the nr_cpus' vulnerability > to unexpected rebooting by broadcast mce. After analysis, I think only the > following first case suffers from the rebooting by broadcast mce. [1-3/4] aims > to fix that issue. I did not understand and read the MCE details, but we previously had a MCE problem, Xunlei fixed in below commit: commit 5bc329503e8191c91c4c40836f062ef771d8ba83 Author: Xunlei Pang Date: Mon Mar 13 10:50:19 2017 +0100 x86/mce: Handle broadcasted MCE gracefully with kexec I wonder if this is same issue or not. Also the old discussion is in below thread: https://lore.kernel.org/patchwork/patch/753530/ Tony raised similar questions, but I'm not sure if it is still a problem or it has been fixed. > > *** Back ground *** > > On x86 it's required to have all logical CPUs set CR4.MCE=1. Otherwise, a > broadcast MCE observing CR4.MCE=0b on any core will shutdown the machine. > > The option 'nosmt' has already complied with the above rule by Thomas's patch. > For detail, refer to 506a66f3748 (Revert "x86/apic: Ignore secondary threads if > nosmt=force") > > But for nr_cpus option, the exposure to broadcast MCE is a little complicated, > and can be categorized into three cases. > > -1. boot up by BIOS. Since no one set CR4.MCE=1, nr_cpus risks rebooting by > broadcast MCE. > > -2. boot up by "kexec -p nr_cpus=". Since the 1st kernel has all cpus' > CR4.MCE=1 set before kexec -p, nr_cpus is free of rebooting by broadcast MCE. > Furthermore, the crashed kernel's wreckage, including page table and text, is > not touched by capture kernel. Hence if MCE event happens on capped cpu, > do_machine_check->__mc_check_crashing_cpu() runs smoothly and returns > immediately, the capped cpu is still pinned on "halt". > > -3. boot up by "kexec -l nr_cpus=". As "kexec -p", it is free of rebooting by > broadcast MCE. But the 1st kernel's wreckage is discarded and changed. when > capped cpus execute do_machine_check(), they may crack the new kernel. But > this is not related with broadcast MCE, and need an extra fix. > > *** Solution *** > "nr_cpus" can not follow the same way as "nosmt". Because nr_cpus limits the > allocation of percpu area and some other kthread memory, which is critical to > cpu hotplug framework. Instead, developing a dedicated SIPI callback > make_capped_cpu_stable() for capped cpu, which does not lean on percpu area to > work. > > [1]: https://lkml.org/lkml/2019/7/5/3 > > To: Gleixner > To: Andy Lutomirski > Cc: Ingo Molnar > Cc: Borislav Petkov > Cc: "H. Peter Anvin" > Cc: Dave Hansen > Cc: Peter Zijlstra > To: x86@kernel.org > Cc: Masami Hiramatsu > Cc: Qian Cai > Cc: Vlastimil Babka > Cc: Daniel Drake > Cc: Jacob Pan > Cc: Michal Hocko > Cc: Eric Biederman > Cc: linux-kernel@vger.kernel.org > Cc: Dave Young > Cc: Baoquan He > Cc: kexec@lists.infradead.org > > --- > Pingfan Liu (4): > x86/apic: correct the ENO in generic_processor_info() > x86/apic: record capped cpu in generic_processor_info() > x86/smp: send capped cpus to a stable state when smp_init() > x86/smp: disallow MCE handler on rebooting AP > > arch/x86/include/asm/apic.h | 1 + > arch/x86/include/asm/smp.h | 3 ++ > arch/x86/kernel/apic/apic.c | 23 ++++++++---- > arch/x86/kernel/cpu/common.c | 7 ++++ > arch/x86/kernel/smp.c | 8 +++++ > arch/x86/kernel/smpboot.c | 83 ++++++++++++++++++++++++++++++++++++++++++++ > kernel/smp.c | 6 ++++ > 7 files changed, 124 insertions(+), 7 deletions(-) > > -- > 2.7.5 > Thanks Dave