[PATCH] x86/mce: Keep quiet in case of broadcasted mce after system panic

[Xunlei Pang]

On 02/16/2017 at 06:18 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 01:36:37PM +0800, Xunlei Pang wrote:
>> I tried to use qemu to inject SRAO("mce -b 0 0 0xb100000000000000 0x5 0x0 0x0"),
>> it works well in 1st kernel, but it doesn't work for 1st kernel after kdump boots(seems
>> the cpus remain in 1st kernel don't respond to the simulated broadcasting mce).
>>
>> But in theory, we know cpus belong to kdump kernel can't respond to the
>> old mce handler, so a single SRAO injection in 1st kernel should be similar.
>> For example, I used "... -smp 2 -cpu Haswell" to launch a simulation with broadcast
>> mce supported, and inject SRAO to cpu0 only through qemu monitor
>> "mce 0 0 0xb100000000000000 0x5 0x0 0x0", cpu0 will timeout/panic and reboot
>> the machine as follows(running on linux-4.9):
>>   Kernel panic - not syncing: Timeout: Not all CPUs entered broadcast exception handler
> Sounds to me like you're trying hard to prove some point of yours which
> doesn't make much sense to me. And when you say "in theory", that makes
> it even less believable. So I remember asking you for exact steps. That
> above doesn't read like steps but like some babbling and I've actually
> tried to make sense of it for a couple of minutes but failed.
>
> So lemme spell it out for ya. I'd like for you to give me this:
>
> 1. Build kernel with this config
> 2. Boot it in kvm with this settings
> 3. Do this in the guest
> 4. Do that in the guest
> 5. ...
> 6. ...
>
>
> And all should be exact commands so that I can do them here on my machine.
>

Sorry, missed your point.

The steps should be as follows:
1. Prepare a multi-core intel machine with broadcasted mce support.
    Enable kdump(crashkernel=256M) and configure kdump kernel to boot with "nr_cpus=1".
2. Activate kdump, and crash the first kernel on some cpu, say cpu1
    (taskset -c 1 echo 0 > /proc/sysrq-trigger), then kdump will boot on cpu1.
3. After kdump boots up(let it enter shell), trigger a SRAO on cpu1
   (QEMU monitor cmd: mce -b 1 0 0xb100000000000000 0x5 0x0 0x0),
    then mce will be broadcast to the other cpus which are still running
    in the first kernel(i.e. looping in crash_nmi_callback).
    If you own some hardware to inject mce, it would be great, as QEMU does not work correctly for me.
4. Then something like below is expected to happen:

[    1.468556] tsc: Refined TSC clocksource calibration: 2933.437 MHz
         Starting Kdump Vmcore Save Service...
kdump: saving to /sysroot//var/crash/127.0.0.1-2015-09-01-05:07:03/
kdump: saving vmcore-dmesg.txt
[   39.000010] mce: [Hardware Error]: CPU 0: Machine Check Exception: 0 Bank 2: bd0000000000017a
[   39.000010] mce: [Hardware Error]: TSC 0 ADDR 61600000 MISC 8c 
[   39.000010] mce: [Hardware Error]: PROCESSOR 0:106a3 TIME 1441083980 SOCKET 0 APIC 0 microcode 1
[   39.000010] mce: [Hardware Error]: Run the above through 'mcelog --ascii'
[   39.000010] Kernel panic - not syncing: Timeout: Not all CPUs entered broadcast exception handler
[   39.000010] Shutting down cpus with NMI
[    1.758463] Uhhuh. NMI received for unknown reason 20 on CPU 0.
[    1.758463] Do you have a strange power saving mode enabled?
[    1.758463] Dazed and confused, but trying to continue
[   39.000010] Rebooting in 30 seconds..

Regards,
Xunlei