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Subject: Re: Linux kernel: powerpc: KVM guest can trigger host crash on Power8
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From: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
To: Michael Ellerman <mpe@ellerman.id.au>
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Hi Michael!

On 1/13/22 01:17, John Paul Adrian Glaubitz wrote:
> On 1/9/22 23:17, John Paul Adrian Glaubitz wrote:
>> On 1/7/22 12:20, John Paul Adrian Glaubitz wrote:
>>>> Can you separately test with (on the host):
>>>>
>>>>  # echo 0 > /sys/module/kvm_hv/parameters/dynamic_mt_modes
>>>
>>> I'm trying to turn off "dynamic_mt_modes" first and see if that makes any difference.
>>>
>>> I will report back.
>>
>> So far the machine is running stable now and the VM built gcc-9 without
>> crashing the host. I will continue to monitor the machine and report back
>> if it crashes, but it looks like this could be it.
> 
> So, it seems that setting "dynamic_mt_modes" actually did the trick, the host is no longer
> crashing. However, I have observed on two occasions now that the build VM is just suddenly
> off as if someone has shut it down using the "force-off" option in the virt-manager user
> interface.

Just as a heads-up. Ever since I set

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

on the host machine, I never saw the crash again. So the issue seems to be related to the
dynamic_mt_modes feature.

Thanks,
Adrian

-- 
 .''`.  John Paul Adrian Glaubitz
: :' :  Debian Developer - glaubitz@debian.org
`. `'   Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
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