In Linux, the CPU affinity (i.e. the list of cores on which a thread may be run) is inherited by any child process or thread, from its parent.
Nevertheless, the CPU affinity of any process or thread can be changed at any time with sched_setaffinity() so the httpd process itself could run its children on different cores, if it wanted so, but it is unlikely that any httpd program does this.
The new feature that is discussed in this thread will limit the cores on which the threads of a user can be scheduled to those having the same cookie, so a process will no longer be able to reschedule its children to run on the same core as the threads of another user.
Yes? If CPU X is the only trusted CPU, or you are only trusted to run your software on that CPU, then everything should run on that core. If you rent 12 of 128 cores, then it may run on any of those 12 cores.
Nevertheless, the CPU affinity of any process or thread can be changed at any time with sched_setaffinity() so the httpd process itself could run its children on different cores, if it wanted so, but it is unlikely that any httpd program does this.
The new feature that is discussed in this thread will limit the cores on which the threads of a user can be scheduled to those having the same cookie, so a process will no longer be able to reschedule its children to run on the same core as the threads of another user.