[$] Emulated iopl()

Operating systems and computing hardware both carry a lot of their history
with them. The x86 I/O-port mechanism is one piece of that history; it is
rarely used by hardware designed in the last 20 years, but it must
still be supported. That doesn't mean that this support can't be cleaned
up and improved, though, especially when the old implementation turns out
to have some unpleasant properties. An example can be seen in the
iopl() patch set from Thomas Gleixner.