[$] Killing processes that don't want to die

Suppose you have a program running on your system that you don't quitetrust. Maybe it's a program submitted by a student to an automatedgrading system. Or maybe it's a QEMU device model running in a Xencontrol domain ("domain 0" or "dom0"), and you want to make surethat even if an attacker from a rogue virtual machine manages to take over the QEMUprocess, they can't do any further harm. There are many things you want to do as faras restricting its ability to do mischief. But one thing in particular you probably want to dois to be able to reliably kill the process once you think it should bedone. This turns out to be quite a bit more tricky than you'd think.