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Memory management
=================

SPARTAN kernel deploys generic interface for 4-level page tables,
no matter what the real underlying hardware architecture is.


 VADDR
 +-----------------------------------------------------------------------------+
 |   PTL0_INDEX  |   PTL1_INDEX   |   PTL2_INDEX   |   PTL3_INDEX   |   OFFSET |
 +-----------------------------------------------------------------------------+


 PTL0                   PTL1                   PTL2                   PTL3
 +--------+             +--------+             +--------+             +--------+
 |        |             |        |             |  PTL3  | -----\      |        |
 |        |             |        |             +--------+      |      |        |
 |        |             +--------+             |        |      |      |        |
 |        |             |  PTL2  | -----\      |        |      |      |        |
 |        |             +--------+      |      |        |      |      |        |
 |        |             |        |      |      |        |      |      +--------+
 +--------+             |        |      |      |        |      |      | FRAME  |
 |  PTL1  | -----\      |        |      |      |        |      |      +--------+
 +--------+      |      |        |      |      |        |      |      |        |
 |        |      |      |        |      |      |        |      |      |        |
 |        |      |      |        |      |      |        |      |      |        |
 +--------+      \----> +--------+      \----> +--------+      \----> +--------+
     ^
     |
     |
 +--------+
 |  PTL0  |
 +--------+


PTL0        Page Table Level 0 (Page Directory)
PTL1        Page Table Level 1
PTL2        Page Table Level 2
PTL3        Page Table Level 3

PTL0_INDEX  Index into PTL0
PTL1_INDEX  Index into PTL1
PTL2_INDEX  Index into PTL2
PTL3_INDEX  Index into PTL3

VADDR       Virtual address for which mapping is looked up
FRAME       Physical address of memory frame to which VADDR is mapped


On architectures whose hardware has fewer levels, PTL2 and, if need be, PTL1 are
left out. TLB-only architectures are to define custom format for software page
tables.