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

[Lukas Straub <lukasstraub2@web.de>]

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On Mon, 2 Feb 2026 09:12:33 -0500
Peter Xu <peterx@redhat.com> wrote:

> On Fri, Jan 30, 2026 at 01:49:42PM +0100, Lukas Straub wrote:
> > 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.  
> 
> This can be mentioned in the commit message.
> 
> IIUC reset() may or may not be required while loading a snapshot.
> Normally, a device reset() should reset all dev registers and internal
> states, OTOH loadvm() will reload most of them once more.. so less
> efficient.
> 
> Maybe there's chance to "fix" q35 instead reducing this overhead, but I'll
> leave that to be your call; to me this fix is clean from maint POV.
> 
> Thanks,
> 

Yes, I think this fix is fine for now. It more correct like this and we
can improve performance later while keeping it correct.

Regards,
Lukas Straub

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