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 <xlpang@xxxxxxxxxx> 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 <tglx@xxxxxxxxxxxxx> > To: Andy Lutomirski <luto@xxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > To: x86@xxxxxxxxxx > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > Cc: Qian Cai <cai@xxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Cc: Daniel Drake <drake@xxxxxxxxxxxx> > Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx > Cc: Dave Young <dyoung@xxxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: kexec@xxxxxxxxxxxxxxxxxxx > > --- > 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@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec