reference: https://github.com/raspberrypi/firmware/issues/542
procsave(Proc* p)
{
uvlong t;
cycles(&t);
p->pcycles += t;
// TODO: save and restore VFPv3 FP state once 5[cal] know the new registers.
fpuprocsave(p);
/*
* Prevent the following scenario:
* pX sleeps on cpuA, leaving its page tables in mmul1
* pX wakes up on cpuB, and exits, freeing its page tables
* pY on cpuB allocates a freed page table page and overwrites with data
* cpuA takes an interrupt, and is now running with bad page tables
* In theory this shouldn't hurt because only user address space tables
* are affected, and mmuswitch will clear mmul1 before a user process is
* dispatched. But empirically it correlates with weird problems, eg
* resetting of the core clock at 0x4000001C which confuses local timers.
*/
if(conf.nmach > 1)
mmuswitch(nil);
}
