Re: [PATCH v1 3/4] arm/sysctl: Implement cpu hotplug ops

[Julien Grall <julien@xxxxxxx>]

Hi Jan,

On 18/09/2025 15:51, Jan Beulich wrote:
> On 18.09.2025 15:35, Julien Grall wrote:
> > On 18/09/2025 13:16, Mykyta Poturai wrote:
> > > +static long cpu_hotplug_sysctl(struct xen_sysctl_cpu_hotplug *hotplug)
> > > +{
> > > +    bool up;
> > > +
> > > +    switch (hotplug->op) {
> > > +        case XEN_SYSCTL_CPU_HOTPLUG_ONLINE:
> > > +            if ( hotplug->cpu == 0 )
> > I can't find a similar check on x86. Do you have any pointer?
> When CPU 0 cannot be brought down (see cpu_down()), tryin to bring it up
> is kind of pointless, and hence can perhaps be short circuited like this?
Thanks for the clarification, I missed the check in cpu_down(). That 
said, I don't see any value to short circuit it. In fact, I see this as 
more a risk because if we ever decide to allow CPU 0 to be offlined, 
then it would be more difficult to find places where we short circuit it.
So I would rather prefer if we remove the checks.

Cheers,

--
Julien Grall