I imagine seccomp and ptrace have pretty similar performance, since they both wake the 'host' using a signal, and stay out of the way until their trigger is met

I imagine seccomp and ptrace have pretty similar performance, since they both wake the 'host' using a signal, and stay out of the way until their trigger is met. As for UML stability, Debian have been providing packages of it for years, I can't remember the last time I built it directly.