Re: [PATCH v8 3/7] crypto/ccp: Disable CPU hotplug while SNP is active

[Kalra, Ashish]

On 6/19/2026 6:20 PM, Borislav Petkov wrote:
> I'd let tglx maybe give a better idea but this cpu_hotplug_disable static var
> in kernel/cpu.c could get a getter function and be used instead of you
> reinventing the wheel in here.

I don't follow — I'm not reinventing anything here. Patch 3 will use the existing CPU-hotplug callback interface: cpuhp_setup_state()
with a down callback that returns -EBUSY to refuse the offline while SNP is active. That's the standard mechanism for conditionally
preventing a CPU offline, and it keeps no private "hotplug disabled" state of its own — so there's nothing here for a getter on
cpu_hotplug_disabled to replace.

I chose the cpuhp callback specifically over cpu_hotplug_disable_offlining(): the callback can be torn down with
cpuhp_remove_state() when SNP is fully shut down, which re-enables CPU offlining. cpu_hotplug_disable_offlining() sets
cpu_hotplug_offline_disabled, which is __ro_after_init and one-way — there's no interface to clear it, and adding one would mean
dropping the __ro_after_init marking and a new core "re-enable offlining" API. So that route can't re-enable offlining on SNP
shutdown without new core plumbing, whereas the cpuhp callback gives me that for free.

Happy to go whichever way you/tglx prefers — if there's a specific variable/getter you had in mind, please point me at it.

Thanks,
Ashish