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From: Mike <michael.heltne@gmail.com>
Date: Thu, 27 Jan 2022 16:50:15 +0100
Message-ID: <CANtoAtPJf6ARWJeQSyro51bwkTfBWvKRZTJeU80LM5=dS4WPig@mail.gmail.com>
Subject: Re: Linux kernel: powerpc: KVM guest can trigger host crash on Power8
To: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
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I just made the huge mistake of hibernating and resuming, I'm going trough
the process of rescue and all, thankfully I had a 2016 cd in the drive.
I'll read up once the sheer panic settles.

-Michael

On Wed, Jan 26, 2022, 21:22 John Paul Adrian Glaubitz <
glaubitz@physik.fu-berlin.de> wrote:

> 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
>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913
>
>

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Content-Transfer-Encoding: quoted-printable

<div dir=3D"auto">I just made the huge mistake of hibernating and resuming,=
 I&#39;m going trough the process of rescue and all, thankfully I had a 201=
6 cd in the drive. I&#39;ll read up once the sheer panic settles.=C2=A0<div=
 dir=3D"auto"><br></div><div dir=3D"auto">-Michael</div></div><br><div clas=
s=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Wed, Jan 26, 202=
2, 21:22 John Paul Adrian Glaubitz &lt;<a href=3D"mailto:glaubitz@physik.fu=
-berlin.de">glaubitz@physik.fu-berlin.de</a>&gt; wrote:<br></div><blockquot=
e class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc sol=
id;padding-left:1ex">Hi Michael!<br>
<br>
On 1/13/22 01:17, John Paul Adrian Glaubitz wrote:<br>
&gt; On 1/9/22 23:17, John Paul Adrian Glaubitz wrote:<br>
&gt;&gt; On 1/7/22 12:20, John Paul Adrian Glaubitz wrote:<br>
&gt;&gt;&gt;&gt; Can you separately test with (on the host):<br>
&gt;&gt;&gt;&gt;<br>
&gt;&gt;&gt;&gt;=C2=A0 # echo 0 &gt; /sys/module/kvm_hv/parameters/dynamic_=
mt_modes<br>
&gt;&gt;&gt;<br>
&gt;&gt;&gt; I&#39;m trying to turn off &quot;dynamic_mt_modes&quot; first =
and see if that makes any difference.<br>
&gt;&gt;&gt;<br>
&gt;&gt;&gt; I will report back.<br>
&gt;&gt;<br>
&gt;&gt; So far the machine is running stable now and the VM built gcc-9 wi=
thout<br>
&gt;&gt; crashing the host. I will continue to monitor the machine and repo=
rt back<br>
&gt;&gt; if it crashes, but it looks like this could be it.<br>
&gt; <br>
&gt; So, it seems that setting &quot;dynamic_mt_modes&quot; actually did th=
e trick, the host is no longer<br>
&gt; crashing. However, I have observed on two occasions now that the build=
 VM is just suddenly<br>
&gt; off as if someone has shut it down using the &quot;force-off&quot; opt=
ion in the virt-manager user<br>
&gt; interface.<br>
<br>
Just as a heads-up. Ever since I set<br>
<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 echo 0 &gt; /sys/module/kvm_hv/parameters/dynam=
ic_mt_modes<br>
<br>
on the host machine, I never saw the crash again. So the issue seems to be =
related to the<br>
dynamic_mt_modes feature.<br>
<br>
Thanks,<br>
Adrian<br>
<br>
-- <br>
=C2=A0.&#39;&#39;`.=C2=A0 John Paul Adrian Glaubitz<br>
: :&#39; :=C2=A0 Debian Developer - <a href=3D"mailto:glaubitz@debian.org" =
target=3D"_blank" rel=3D"noreferrer">glaubitz@debian.org</a><br>
`. `&#39;=C2=A0 =C2=A0Freie Universitaet Berlin - <a href=3D"mailto:glaubit=
z@physik.fu-berlin.de" target=3D"_blank" rel=3D"noreferrer">glaubitz@physik=
.fu-berlin.de</a><br>
=C2=A0 `-=C2=A0 =C2=A0 GPG: 62FF 8A75 84E0 2956 9546=C2=A0 0006 7426 3B37 F=
5B5 F913<br>
<br>
</blockquote></div>

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