ARM64 KVM crash

[marc.zyngier@arm.com (Marc Zyngier)]

On Fri, 12 Oct 2018 19:59:16 +0100,
Mikulas Patocka <mpatocka@redhat.com> wrote:
> 
> 
> 
> On Fri, 12 Oct 2018, Marc Zyngier wrote:
> 
> > Right. But how is that related to KVM? See below:
> > 
> > > [75476.680725]  find_next_and_bit+0xc/0x70
> > > [75476.680728]  find_busiest_group+0x128/0x938
> > > [75476.680730]  load_balance+0x148/0x848
> > > [75476.680732]  pick_next_task_fair+0x1d4/0x568
> > > [75476.680734]  __schedule+0xe8/0x4b0
> > > [75476.680736]  schedule+0x38/0xa0
> > > [75476.680739]  kvm_vcpu_block+0x88/0x180
> > > [75476.680742]  kvm_handle_wfx+0x80/0xb8
> > > [75476.680744]  handle_exit+0x138/0x1b8
> > 
> > The guest is exiting because it has executed a blocking WFI, so KVM's
> > job is done and we're calling schedule(). The scheduler then starts
> > doing its job of picking the next victim.
> > 
> > At this stage, the kernel indeed blows up. But this doesn't immediately
> > seem to be KVM's fault. It is far more likely that the scheduler has
> > messed something up in its own data structure, which is even worse :-(.
> > 
> > I'd suggest you get in touch with the scheduler guys to see if they have
> > any insight. Also, trying to come up with a reproducer would be
> > extremely useful.
> > 
> > Thanks,
> > 
> > 	M.
> 
> I use this machine most of the time without KVM - and it crashed when I 
> started KVM - so I assume that KVM had something to do with it. Perhaps it 
> corrupts random memory? I may try to run some KVM stress for many days to 
> test if I reproduce it.

One thing I know for sure is that if you use a tap (such as macvtap)
to give networking to your VMs, the Ethernet driver on the 8040 (such
as on your MacchiatoBin) will happily corrupt memory (you can witness
that without running KVM at all). Something to do with the sbk being
freed early.

I've reported this issue several times, only to hear the wind
blowing. At this stage, I've shelved it. There is enough decent and
maintained platforms around not to worry about the unmaintained stuff.

Now, if you can give me a reproducer, I'll happily investigate.

Thanks,

	M.

-- 
Jazz is not dead, it just smell funny.