Re: [PATCH 2/6] migration/colo.c: Use cpu_synchronize_all_states()

[Lukas Straub <lukasstraub2@web.de>]

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On Wed, 13 May 2020 10:47:02 +0100
"Dr. David Alan Gilbert" <dgilbert@redhat.com> wrote:

> * Lukas Straub (lukasstraub2@web.de) wrote:
> > cpu_synchronize_all_pre_loadvm() marks all vcpus as dirty, so the
> > registers are loaded from CPUState before we continue running
> > the vm. However if we failover during checkpoint, CPUState is not
> > initialized and the registers are loaded with garbage. This causes
> > guest hangs and crashes.
> > 
> > Fix this by using cpu_synchronize_all_states(), which initializes
> > CPUState from the current cpu registers additionally to marking
> > the vcpus as dirty.
> > 
> > Signed-off-by: Lukas Straub <lukasstraub2@web.de>  
> 
> OK, so I think you're saying that if the qemu_loadvm_state_main fails
> because we failover, we now have duff CPU state, where we should just
> carry on running on the secondary with the current state, so yes

Exactly, Sorry for my bad wording.

> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> > ---
> >  migration/colo.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/migration/colo.c b/migration/colo.c
> > index 09168627bc..6b2ad35aa4 100644
> > --- a/migration/colo.c
> > +++ b/migration/colo.c
> > @@ -696,7 +696,7 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
> >      }
> >  
> >      qemu_mutex_lock_iothread();
> > -    cpu_synchronize_all_pre_loadvm();
> > +    cpu_synchronize_all_states();
> >      ret = qemu_loadvm_state_main(mis->from_src_file, mis);
> >      qemu_mutex_unlock_iothread();
> >  
> > -- 
> > 2.20.1
> >   
> 
> 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
> 


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