Re: [PATCH 0/4] x86/mce: protect nr_cpus from rebooting by broadcast mce

[Thomas Gleixner]

On Wed, 7 Aug 2019, Pingfan Liu wrote:
> 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 <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.
> > 
>
> Xunlei's patch is the precondition of the stability for the case 2: boot
> up by "kexec -p nr_cpus="

Correct. The only dangerous issue which is then left is that an MCE hits
_before_ all CPUs have CR.MCE=1 set. That's a general issue also for cold
boot. Thanks to the brilliant hardware design, all we can do is pray....

> 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.

Pingfan, please trim your replies and remove the useless gunk after your answer.

Thanks,

	tglx