On Mon, Oct 11, 2021 at 03:19:37PM +0100, Szabolcs Nagy wrote:

> if fork resets tpidr2 then returning to a stack frame
> that set tpidr2 could cause clobbered za state.
> (userspace can fix this up, but if we want this case
> to work then it's better to fix it on the kernel side)

OK, that makes sense.  I've changed the code and the kselftest so that
TPIDR2 is preserved on thread creation.