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!
>
> On 10/27/21 07:30, Michael Ellerman wrote:
>> I did test the repro case you gave me before (in the bugzilla), which
>> was building glibc, that passes for me with a patched host.
>
> Did you manage to crash the unpatched host?

Yes, the parallel builds of glibc you described crashed the unpatched
host 100% reliably for me.

I also have a standalone reproducer I'll send you.

> If the unpatched host crashes for you but the patched doesn't, I will
> make sure I didn't accidentally miss anything.

OK thanks.

> Also, I'll try a kernel from git with Debian's config.
>
>> I guess we have yet another bug.
>> 
>> I tried the following in a debian BE VM and it completed fine:
>> 
>>  $ dget -u http://ftp.debian.org/debian/pool/main/g/git/git_2.33.1-1.dsc
>>  $ sbuild -d sid --arch=powerpc --no-arch-all git_2.33.1-1.dsc
>> 
>> Same for ppc64.
>> 
>> And I also tried both at once, repeatedly in a loop.
>
> Did you try building gcc-11 for powerpc and ppc64 both at once?

No, I will try that now.

>> I guess it's something more complicated.
>> 
>> What exact host/guest kernel versions and configs are you running?
>
> Both the host and guest are running Debian's stock 5.14.12 kernel. The host has
> a kernel with your patches applied, the guest doesn't.

OK that sounds fine.

I tested upstream stable v5.14.13 + my patches, but there's nothing
betwen 5.14.12 and 5.14.13 that should matter AFAICS.

> Let me do some more testing.

Thanks.

cheers