SMP - Process is stopped when VM modifies the page tables

- RTS_VMINHIBIT flag is used to stop process while VM is fiddling with
  its pagetables

- more generic way of sending synchronous scheduling events among cpus

- do the x-cpu smp sched calls only if the target process is runnable.
  If it is not, it cannot be running and it cannot become runnable
  this CPU holds the BKL

kernel/system/do_runctl.c

@@ -56,13 +56,13 @@ PUBLIC int do_runctl(struct proc * caller, message * m_ptr)
 	  /* check if we must stop a process on a different CPU */
 	  if (rp->p_cpu != cpuid) {
 		  smp_schedule_stop_proc(rp);
-		  assert(RTS_ISSET(rp, RTS_PROC_STOP));
 		  break;
 	  }
 #endif
 	  RTS_SET(rp, RTS_PROC_STOP);
 	break;
   case RC_RESUME:
+	assert(RTS_ISSET(rp, RTS_PROC_STOP));
 	RTS_UNSET(rp, RTS_PROC_STOP);
 	break;
   default:

kernel/system/do_vmctl.c

@@ -140,6 +140,23 @@ PUBLIC int do_vmctl(struct proc * caller, message * m_ptr)
 		return arch_phys_map_reply(m_ptr->SVMCTL_VALUE,
 			(vir_bytes) m_ptr->SVMCTL_MAP_VIR_ADDR);
 	}
+	case VMCTL_VMINHIBIT_SET:
+		/* check if we must stop a process on a different CPU */
+#if CONFIG_SMP
+		if (p->p_cpu != cpuid) {
+			smp_schedule_vminhibit(p);
+		} else
+#endif
+			RTS_SET(p, RTS_VMINHIBIT);
+		return OK;
+	case VMCTL_VMINHIBIT_CLEAR:
+		assert(RTS_ISSET(p, RTS_VMINHIBIT));
+		/*
+		 * the processes is certainly not runnable, no need to tell its
+		 * cpu
+		 */
+		RTS_UNSET(p, RTS_VMINHIBIT);
+		return OK;
   }
 
   /* Try architecture-specific vmctls. */