Store a reference to a page directory (cr3 register) with each task and switch the cr3 register with each context switch.

Author: tthomps

MyOS_1/Tasks/Context.h

@@ -22,6 +22,7 @@ typedef struct CONTEXT_INFO
     bool inUse;
     bool exclusive; // True to disable switching to any other tasks
     uint32_t PID;
+    uint32_t cr3;
     // ? What else?
 } CONTEXT_INFO, PROCESS_CONTROL_BLOCK;
 

MyOS_1/Tasks/Dispatcher.c

@@ -99,7 +99,7 @@ void DispatchNewTask(uint32_t programStart, uint32_t stackSize, const char *imag
         push [stackPtr]
         int SYSCALL_DISPATCH_NEW_TASK   // call dispatch_new_task_interrupt_handler(eflags, cs, stackPtr, esp)
         add esp, 8
-    }   
+    }
 
     // Update the task's "stack image" to represent values appropriate for the new task
     TASK_STACK_LAYOUT *pNewTask = (TASK_STACK_LAYOUT *)((unsigned long)stackPtr - sizeof(TASK_STACK_LAYOUT));    
@@ -110,6 +110,7 @@ void DispatchNewTask(uint32_t programStart, uint32_t stackSize, const char *imag
 
     tasks[taskSlot].ESP = (uint32_t)pNewTask;
     tasks[taskSlot].exclusive = exclusive;
+    tasks[taskSlot].cr3 = __readcr3();  // TEMPTEMP: Give the new task the same page table as the kernel
 
     // If a GUI shell is running, tell it about the new process
     if (guiCallback)

MyOS_1/Timers/PIT.c

@@ -85,11 +85,12 @@ void _declspec(naked) timer_interrupt_handler(void)
         if (ticksLeftInTask <= 0 && multiEnable)
         {
             if(debugLevel)
-                kprintf("Saving %s\n", tasks[currentTask].imageName);
+                kprintf("Saving %s.", tasks[currentTask].imageName);
 
             // Save current context
             _asm mov[espVal], esp            
             tasks[currentTask].ESP = espVal;
+            tasks[currentTask].cr3 = __readcr3();
 
             oldTaskIndex = currentTask;
 
@@ -114,13 +115,16 @@ void _declspec(naked) timer_interrupt_handler(void)
             else
             {
                 readyQueueHead->taskIndex = oldTaskIndex;
-            }            
+            }
 
             if(debugLevel)
-                kprintf("Switching to %s\n", tasks[currentTask].imageName);
+                kprintf(" Switching to %s\n", tasks[currentTask].imageName);
 
             ticksLeftInTask = TICKS_PER_TASK;
 
+            // switch to the new task's page tables
+            __writecr3(tasks[currentTask].cr3);
+
             // Get the stack pointer of the next waiting task and make that the stack
             espVal = tasks[currentTask].ESP;