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mm.txt

mm.txt 2.1 KB
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  1. 

  2. <previous description obsolete, deleted>
    3. 

  3. 

  4. Virtual memory map with 4 level page tables:
    5. 

  5. 

  6. 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm
    7. 

  7. hole caused by [48:63] sign extension
    8. 

  8. ffff800000000000 - ffff87ffffffffff (=43 bits) guard hole, reserved for hypervisor
    9. 

  9. ffff880000000000 - ffffc7ffffffffff (=64 TB) direct mapping of all phys. memory
    10. 

  10. ffffc80000000000 - ffffc8ffffffffff (=40 bits) hole
    11. 

  11. ffffc90000000000 - ffffe8ffffffffff (=45 bits) vmalloc/ioremap space
    12. 

  12. ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
    13. 

  13. ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
    14. 

  14. ... unused hole ...
    15. 

  15. ffffec0000000000 - fffffbffffffffff (=44 bits) kasan shadow memory (16TB)
    16. 

  16. ... unused hole ...
    17. 

  17. ffffff0000000000 - ffffff7fffffffff (=39 bits) %esp fixup stacks
    18. 

  18. ... unused hole ...
    19. 

  19. ffffffef00000000 - fffffffeffffffff (=64 GB) EFI region mapping space
    20. 

  20. ... unused hole ...
    21. 

  21. ffffffff80000000 - ffffffff9fffffff (=512 MB)  kernel text mapping, from phys 0
    22. 

  22. ffffffffa0000000 - ffffffffff5fffff (=1526 MB) module mapping space
    23. 

  23. ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
    24. 

  24. ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
    25. 

  25. 

  26. The direct mapping covers all memory in the system up to the highest
    27. 

  27. memory address (this means in some cases it can also include PCI memory
    28. 

  28. holes).
    29. 

  29. 

  30. vmalloc space is lazily synchronized into the different PML4 pages of
    31. 

  31. the processes using the page fault handler, with init_level4_pgt as
    32. 

  32. reference.
    33. 

  33. 

  34. Current X86-64 implementations support up to 46 bits of address space (64 TB),
    35. 

  35. which is our current limit. This expands into MBZ space in the page tables.
    36. 

  36. 

  37. We map EFI runtime services in the 'efi_pgd' PGD in a 64Gb large virtual
    38. 

  38. memory window (this size is arbitrary, it can be raised later if needed).
    39. 

  39. The mappings are not part of any other kernel PGD and are only available
    40. 

  40. during EFI runtime calls.
    41. 

  41. 

  42. Note that if CONFIG_RANDOMIZE_MEMORY is enabled, the direct mapping of all
    43. 

  43. physical memory, vmalloc/ioremap space and virtual memory map are randomized.
    44. 

  44. Their order is preserved but their base will be offset early at boot time.
    45. 

  45. 

  46. -Andi Kleen, Jul 2004
    47. 

  47.