Well, it might be possible for a clever simulation to commandeer the bare metal of the system with a well-crafted injection attack, and then use the ring zero access as an environment to stage and control it's own simulation.
This would still consume resources, and indeed, if limited resources were somehow improperly allocated in a catastrophic manner, it might tear apart the fabric of the universe and threaten to crash both simulations.
But think of some of the implications in this. First: when that simulation attempted to discover if it was wrapped in a simulation, it probably would get a false negative, because it'd be running so close to the hardware. Second: WE wouldn't be able to tell if WE were slaved by another simulation. That is, whether we had a parallel universe as a neighbor that was pulling our strings. Third: If we find ourselves creating simulations that are alarmingly convincing, and seem to prove that WE are a simulation, we would want to be very careful when we start playing with one, for fear that we might have unwittingly stumbled upon a curious vulnerability in this realm that allows for an injection attack, since it might crash the system (although, if this is all just a big video game, what is there to honestly fear...).
This would still consume resources, and indeed, if limited resources were somehow improperly allocated in a catastrophic manner, it might tear apart the fabric of the universe and threaten to crash both simulations.
But think of some of the implications in this. First: when that simulation attempted to discover if it was wrapped in a simulation, it probably would get a false negative, because it'd be running so close to the hardware. Second: WE wouldn't be able to tell if WE were slaved by another simulation. That is, whether we had a parallel universe as a neighbor that was pulling our strings. Third: If we find ourselves creating simulations that are alarmingly convincing, and seem to prove that WE are a simulation, we would want to be very careful when we start playing with one, for fear that we might have unwittingly stumbled upon a curious vulnerability in this realm that allows for an injection attack, since it might crash the system (although, if this is all just a big video game, what is there to honestly fear...).
See also: Bobby Tables: http://xkcd.com/327/