Re: [PATCH] hw/intc/xics: Add missing call to register vmstate_icp_server

[Miles Glenn <milesg@linux.ibm.com>]

On Tue, 2025-08-19 at 12:59 +0530, Harsh Prateek Bora wrote:
> + Gautam, Glenn
> 
> Hi Fabian,
> 
> 
> On 8/19/25 08:25, Fabiano Rosas wrote:
> > Fabian Vogt <fvogt@suse.de> writes:
> > 
> > +CC Peter
> > 
> > > An obsolete wrapper function with a workaround was removed entirely,
> > > without restoring the call it wrapped.
> > > 
> > > Without this, the guest is stuck after savevm/loadvm.
> > > 
> > 
> > I'd note that this only affects guests that have actually negotiated
> > XICS, so guests using ic-mode=xive are safe.
> 
> Since this affected only guests using XICS, would it be a better idea to 
> mention this explicitly in commit log as well (?
> 
> > With this patch, backward migration to QEMU versions >= 9.2 is
> > broken. Which I can only assume is ok, since the hard break (vmstate
> > gets rejected) is better than weird post-migration hangs.
> > 
> > If the PPC folks can spot a scenario where migration would provide
> > reasonable results even without the emulated interrupt controller state
> > being migrated, then we'll need a compat property for this.
> > 

I don't know much about the XICS controller, but migration without
restoring the interrupt controller state seems pretty risky to me.  I
wouldn't recommend it.

Glenn

> > Also, a 9.2 guest cannot move to a more recent QEMU version without a
> > reboot. If this is an important scenario, then the new QEMU needs to
> > provide some compatibility knob.
> 
> Gautam, Glenn - thoughts on above comments?
> 
> Thanks for the patch.
> 
> regards,
> Harsh
> 
> > Otherwise:
> > 
> > Acked-by: Fabiano Rosas <farosas@suse.de>
> > Cc: qemu-stable@nongnu.org