From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pl1-x644.google.com ([2607:f8b0:4864:20::644]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hvGkT-00072j-P5 for kexec@lists.infradead.org; Wed, 07 Aug 2019 07:52:48 +0000 Received: by mail-pl1-x644.google.com with SMTP id k8so39528413plt.3 for ; Wed, 07 Aug 2019 00:52:40 -0700 (PDT) Date: Wed, 7 Aug 2019 15:52:26 +0800 From: Pingfan Liu Subject: Re: [PATCH 0/4] x86/mce: protect nr_cpus from rebooting by broadcast mce Message-ID: <20190807075226.GA10392@mypc> References: <1564995539-29609-1-git-send-email-kernelfans@gmail.com> <20190807025843.GA4776@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190807025843.GA4776@dhcp-128-65.nay.redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Dave Young Cc: Dave Hansen , Baoquan He , tony.luck@intel.com, Peter Zijlstra , kexec@lists.infradead.org, Jacob Pan , x86@kernel.org, Michal Hocko , linux-kernel@vger.kernel.org, Daniel Drake , Ingo Molnar , Borislav Petkov , Masami Hiramatsu , Andy Lutomirski , "H. Peter Anvin" , Qian Cai , Thomas Gleixner , Xunlei Pang , Vlastimil Babka , Eric Biederman On Wed, Aug 07, 2019 at 11:00:41AM +0800, Dave Young wrote: > 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. > Xunlei's patch is the precondition of the stability for the case 2: boot up by "kexec -p nr_cpus=" For case1/3, extra effort is needed. Thanks, Pingfan > > > > *** 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 _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec