Re: [PATCH v3 05/10] colo: Fix crash during device vmstate load

[Lukas Straub <lukasstraub2@web.de>]

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On Tue, 27 Jan 2026 15:38:55 -0500
Peter Xu <peterx@redhat.com> wrote:

> On Sun, Jan 25, 2026 at 09:40:10PM +0100, Lukas Straub wrote:
> > With colo we load device vmstate during each checkpoint, on top of
> > a vm that was already running. Some devices expect a reset before
> > loading vmstate on such a previously running vm.
> > 
> > This fixes a crash when using COLO with Q35 machine.
> > 
> > Signed-off-by: Lukas Straub <lukasstraub2@web.de>  
> 
> Yes makes sense, maybe you can add some comments into the code too since
> this was overlooked before,
> 
> Reviewed-by: Peter Xu <peterx@redhat.com>
> 
> Have you tried to measure how many overheads will this introduce to loading
> each snapshot?

It's a large overhead actually, between 10-20 milliseconds.

Regards,
Lukas Straub

> 
> > ---
> >  migration/colo.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/migration/colo.c b/migration/colo.c
> > index db783f6fa77500386d923dd97e522883027e71d8..627b3706687036554eda3909b4194116a7640493 100644
> > --- a/migration/colo.c
> > +++ b/migration/colo.c
> > @@ -727,6 +727,7 @@ static void colo_incoming_process_checkpoint(MigrationIncomingState *mis,
> >  
> >      bql_lock();
> >      vmstate_loading = true;
> > +    qemu_system_reset(SHUTDOWN_CAUSE_SNAPSHOT_LOAD);
> >      colo_flush_ram_cache();
> >      ret = qemu_load_device_state(fb, errp);
> >      if (ret < 0) {
> > 
> > -- 
> > 2.39.5
> >   
> 


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