Hi @kib,
I read your comments from kern_membarrier.c
Please can you correct me if I'm wrong "The function returns a mask of the CPUs where the given pmap is active(Here a CPU is active for a pmap if its using address space represented by that pmap). CPUs that switch context during the call might be missed, so the caller must ensure synchronization or otherwise the result could be invalid immediately after the call." I'll add this in a separate NOTE section

In D56143#1284104, @kib wrote:

Also it probably worth explaining what 'active' means.

Thank you Maxim for the review