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

[Kalra, Ashish]

On 6/18/2026 4:35 PM, Dave Hansen wrote:
> On 6/15/26 12:49, Ashish Kalra wrote:
>> +	/*
>> +	 * Disable CPU hotplug while SNP is active.  Guard against stacking
>> +	 * the disable count: the legacy SNP_SHUTDOWN_EX path clears
>> +	 * snp_initialized without re-enabling hotplug, so this can run
>> +	 * again while hotplug is already disabled.
>> +	 */
>> +	if (!snp_cpu_hotplug_disabled) {
>> +		cpu_hotplug_disable();
>> +		snp_cpu_hotplug_disabled = true;
>> +	}
> 
> This seems like a hack, guys.
> 
> cpu_hotplug_disable() seems like more of a temporary lock than enforcing
> basically permanent system state.
> 
> This seems like it would be better implemented by registering a CPU
> hotplug callback and then refusing to offline if sev->snp_initialized is
> set.
> 
> snp_setup_rmpopt() can be run any time, right? It doesn't need to be
> after sev->snp_initialized=1.

Yes, snp_setup_rmpopt() doesn't depend on snp_initialized. Programming RMPOPT_BASE only needs
the CPU online and the system rmpopt_capable.

Based on Dave's feedback, i am going to drop this cpu_hotplug_disable()/cpu_hotplug_enable()
and instead implementing and registering the CPU hotplug callback and then refusing to go offline
if SNP is enabled, unless anyone else here has a different thought/suggestion.

Thanks,
Ashish