Some questions about exceptions?

[loody <miloody@gmail.com>]

Dear all:
When I read mips spec there is an exception called MCheck and my questions are:
1. Does this exception only happen on write?
2. The spec says this exception happens when following conditions matched:
    a. Existing Page Valid Bit = 1
    b. Written Page Valid Bit = 1
    what is the correct definition of "Existing Page" and "Written Page"?
    I guess the definition of "Written Page" is teh PFN we get from TLB.
    But what is "Existing Page"?
3. I google a paragraph which discuss about this exception,
http://www.spinics.net/lists/mips/msg19804.html
   But I cannot find the reason why it happened from the log.
   The entries in TLB seems fine.

BTW, where I can find kernel
1. first time fill Page blobal directory
2. handle
  a. tlb refill, invalid and modified?

appreciate your help,
miloody