Re: [PATCH] s390/smp: Reflect (de)configured CPUs to cpu_enabled_mask

[Vasily Gorbik <gor@linux.ibm.com>]

On Thu, Jul 23, 2026 at 03:36:43PM +0200, Mete Durlu wrote:
> On s390, CPUs can be in a state where it is not possible to hotplug
> them online before certain prequisite steps. For example the CPUs which
> get introduced during runtime of a system can posses a "deconfigured"
> state which prevents them from being hotplugged online before they get
> configured. Another case is when users set the configured state of CPUs
> themselves via "chcpu" or sysfs attributes.
> 
> On s390 available CPUs are being registered as new devices via
> smp_add_core() either during boot or after a CPU rescan (for newly added
> CPUs during runtime). Registered CPUs are marked as enabled without
> considering the configure states. Add necessary checks to smp_add_core()
> and userspace configure attribute handler. Reflect the configured CPUs
> to cpu_enabled_mask to correctly represent which CPUs can be hotplugged
> online.
> 
> Signed-off-by: Mete Durlu <meted@linux.ibm.com>
> ---
> 4e1a7df45480 ("cpumask: Add enabled cpumask for present CPUs that can
> be brought online") introduces a new cpumask to signify which CPUs can
> be hotplugged online at a given time.
> 
> Originally the concept is introduced to reflect CPUs which are being
> kept offline by firmware decisions. For s390 the configure state of the
> CPUs matches this concept. CPUs can assume configured or deconfigured
> state. When a CPU is in deconfigured state, it cannot be brought online
> util it is back in configured state.
>  
> On s390 available CPUs are being registered as new devices via
> smp_add_core() either during boot or after a CPU rescan (for newly added
> CPUs during runtime). Registered CPUs are marked as enabled without
> considering the configure states. Add necessary checks to smp_add_core()
> and userspace configure attribute handler. Reflect the configured CPUs
> to cpu_enabled_mask to correctly represent which CPUs can be hotplugged
> online.
> ---
>  arch/s390/kernel/smp.c | 5 +++++
>  1 file changed, 5 insertions(+)

Applied, thank you!