1. A multiprocessing system, comprising: a multithreading microprocessor, comprising: a plurality of thread contexts (TCs); a translation lookaside buffer (TLB), shared by said plurality of TCs; and an instruction scheduler, coupled to said plurality of TCs, configured to dispatch to execution units, in a multithreaded fashion, instructions of threads executing on said plurality of TCs; and a multiprocessor operating system (OS), configured to schedule execution of said threads on said plurality of TCs, wherein a thread of said threads executing on one of said plurality of TCs is configured to update said shared TLB, and prior to updating said TLB to: disable interrupts, to prevent said OS from unscheduling said TLB-updating thread from executing on said plurality of TCs; and disable said instruction scheduler from dispatching instructions from any of said plurality of TCs except from said one of said plurality of TCs on which said TLB-updating thread is executing.