linux/Documentation/x86/x86_64/mm.txt
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   2<previous description obsolete, deleted>
   3
   4Virtual memory map with 4 level page tables:
   5
   60000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
   7hole caused by [48:63] sign extension
   8ffff800000000000 - ffff80ffffffffff (=40 bits) guard hole
   9ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
  10ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
  11ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
  12ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
  13ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
  14... unused hole ...
  15ffffffff80000000 - ffffffffa0000000 (=512 MB)  kernel text mapping, from phys 0
  16ffffffffa0000000 - fffffffffff00000 (=1536 MB) module mapping space
  17
  18The direct mapping covers all memory in the system up to the highest
  19memory address (this means in some cases it can also include PCI memory
  20holes).
  21
  22vmalloc space is lazily synchronized into the different PML4 pages of
  23the processes using the page fault handler, with init_level4_pgt as
  24reference.
  25
  26Current X86-64 implementations only support 40 bits of address space,
  27but we support up to 46 bits. This expands into MBZ space in the page tables.
  28
  29-Andi Kleen, Jul 2004
  30
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