Linux kernel: powerpc: KVM guest can trigger host crash on Power8

[Michael Ellerman]

John Paul Adrian Glaubitz <glaubitz at physik.fu-berlin.de> writes:
> Hi Michael!
>
> Sorry for the long time without any responses. Shall we continue debugging this?

Yes!

Sorry also that I haven't been able to fix it yet, I had to stop chasing
this bug and work on other things before the end of the year.

> We're currently running 5.15.x on the host system and the guests and the testsuite
> for gcc-9 still reproducibly kills the KVM host.

Have you been able to try the different -smp options I suggested?

Can you separately test with (on the host):

 # echo 0 > /sys/module/kvm_hv/parameters/dynamic_mt_modes


cheers

> On 11/1/21 07:53, Michael Ellerman wrote:
>> Sure, will give that a try.
>> 
>> I was able to crash my machine over the weekend, building openjdk, but I
>> haven't been able to reproduce it for ~24 hours now (I didn't change
>> anything).
>> 
>> 
>> Can you try running your guests with no SMT threads?
>> 
>> I think one of your guests was using:
>> 
>>   -smp 32,sockets=1,dies=1,cores=8,threads=4
>> 
>> Can you change that to:
>> 
>>   -smp 8,sockets=1,dies=1,cores=8,threads=1
>> 
>> 
>> And something similar for the other guest(s).
>> 
>> If the system is stable with those settings that would be useful
>> information, and would also mean you could use the system without it
>> crashing semi regularly.
>> 
>> cheers
> -- 
>  .''`.  John Paul Adrian Glaubitz
> : :' :  Debian Developer - glaubitz at debian.org
> `. `'   Freie Universitaet Berlin - glaubitz at physik.fu-berlin.de
>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913