Ex.1
               +------------+            +------------+ 
   0xf0f02ffc  | 0xf00f3007 | 0xff005ffc | 0xbebeebee | 
               +------------+            +------------+ 
               | ...        |            | ...        | 
               +------------+            +------------+ 
   0xf0f02800  | 0xff005007 | 0xff005800 | 0xf00f8000 | 
               +------------+            +------------+ 
               | ...        |            | ...        | 
               +------------+            +------------+ 
   0xf0f02000  | 0xffff5007 | 0xff005000 | 0xc5201000 | 
               +------------+            +------------+ 

               +------------+            +------------+
    0xffff1ffc | 0xd5202007 | 0xffff5ffc | 0xdeadbeef |
               +------------+            +------------+				 
               | ...        |            | ...        |				 
               +------------+            +------------+				 
    0xffff1800 | 0xff005007 | 0xffff5800 | 0xff005000 |				 
               +------------+            +------------+				 
               | ...        |            | ...        |				 
               +------------+            +------------+				 
    0xffff1000 | 0xf0f02007 | 0xffff5000 | 0xc5202000 |				 
               +------------+            +------------+				 

The content of %cr3 (the pointer to the page directory) is 0xffff1000.

Output of this is:
 int *ptr1 = (int *) 0x0;
 int *ptr2 = (int *) 0x200ffc;
 printf("%x\n", *ptr1);
 printf("%x\n", *ptr2);


Ex.2 
- TLB / page faults

Assuming 0x200000 and 0x300000 are stored on disk
  [context switch - tlb is flushed (x86)]
  0x500     movl 0x200000, %eax    # move data in 0x200000 to register %eax
  0x504     incl %eax, 1           # add one to %eax
  0x508     movl %eax, 0x300000    # move %eax to memory location 0x300000

  0x512     push %ecx              # push %ecx onto the stack

How many tlb misses? 

How many page faults? 


MemOS:

- Kernel virtual address
  Kernel is setup to use an identity mapping
  [0, MEMSIZE_PHYSICAL) -> [0, MEMSIZE_PHYSICAL)

- Physical pages' meta data is recorded in page_info array,
    whose elements contains refcount, owner
    owner can be kernel, reserved, free, or pid

- Process control block:
  * Your usual process registers, process state
  * Process page table - a pointer (?) to a page directory
  * Page directory's first entry points to a page table
  Our job mainly consists of manipulating the page tables, and page info array

- Useful functions to implement for said manipulations:
  * find a PO_FREE physical page and assign it to a process (Ex2, 3, 4, 5)
  * allocate empty page dir + page table for a process (Ex2, 4)
  * make a copy of existing page table and assign it to a process (Ex2, 5)
  * implement your own helper functions as you see fit
Tip: Zero the allocated page before using it!! (memset)

- Some useful functions/macros:
   PTE_ADDR : PTE_ENTRY -> Physical address
   PAGENUMBER : a phyiscal address -> corresponding index into page info array 
   PAGEADDR : PAGENUMBER^{-1}
   virtual_memory_lookup(pagetable, va)