Re: [PATCH 2/6] x86/sev: add support for enabling RMPOPT

[K Prateek Nayak]

Hello Dave,

On 2/18/2026 3:36 AM, Dave Hansen wrote:
>> +/*
>> + * Build a cpumask of online primary threads, accounting for primary threads
>> + * that have been offlined while their secondary threads are still online.
>> + */
>> +static void get_cpumask_of_primary_threads(cpumask_var_t cpulist)
>> +{
>> +	cpumask_t cpus;
>> +	int cpu;
>> +
>> +	cpumask_copy(&cpus, cpu_online_mask);
>> +	for_each_cpu(cpu, &cpus) {
>> +		cpumask_set_cpu(cpu, cpulist);
>> +		cpumask_andnot(&cpus, &cpus, cpu_smt_mask(cpu));
>> +	}
>> +}
> 
> Don't we have a primary thread mask already? I thought we did.

If you are referring to cpu_primary_thread_mask(), the CPUs are set on it
based on the LSB of APICID, specifically:

    !(apicid & (__max_threads_per_core - 1))

It can so happen, the primary thread ((apicid & 1) == 0) of the core is
offline while the secondary thread ((apicid & 1) == 1) is online but the
traversal of (cpu_primary_thread_mask() & cpu_online_mask()) will simply
skip these cores.

Is there an equivalent mask that sets the first online CPU of each core?

-- 
Thanks and Regards,
Prateek