title: What's meaning of each bit of machine frame address for xen 64bit
body: <p>I'm using xen 4.30 64bit. I know that only 48bits are used to index the machine address. 
  The last 12 bits (A0-A11) are the offset of each page, and A12-A47 are the mfn. </p>
  
  <p>I remembered some two bits of the last 12 bits are used for privilege control, but cannot remember which two bits are. </p>
  
  <p>In addition, I want to know how xen uses the last 12 bits to do the page control.</p>
  
  <p>I really appreciate your help if you could point me to some link that explain the last 12 bits. </p>
  
  <p>Thank you very much!</p>