Commit fd10f08c authored by Will Deacon's avatar Will Deacon
Browse files

Documentation: arm64: Remove stale and redundant virtual memory diagrams 

The arm64 'memory.rst' file tries to document the virtual memory map
and the translation procedure for a couple of kernel configurations.

Unfortunately, the virtual memory map changes relatively frequently and
we support considerably more configurations than we did when the docs
were introduced (e.g. we now have support for 16KiB pages and 52-bit
addressing). Furthermore, the Arm ARM is the definitive resource for the
translation procedure and so there's little point in duplicating part
of that information in the kernel documentation.

Rather than continue trying (and failing) to maintain these diagrams,
let's rip them out. The kernel page-table can be dumped using
CONFIG_PTDUMP_DEBUGFS if necesssary.

Link: https://lore.kernel.org/r/20250102065554.1533781-1-sangmoon.kim@samsung.com


Reported-by: default avatarSangmoon Kim <sangmoon.kim@samsung.com>
Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 1e4a5e36

Documentation/arch/arm64/memory.rst

+0 −65
Original line number Diff line number Diff line
@@ -23,71 +23,6 @@ swapper_pg_dir contains only kernel (global) mappings while the user pgd 
contains only user (non-global) mappings.  The swapper_pg_dir address is

written to TTBR1 and never written to TTBR0.





AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit)::



  Start			End			Size		Use

  -----------------------------------------------------------------------

  0000000000000000	0000ffffffffffff	 256TB		user

  ffff000000000000	ffff7fffffffffff	 128TB		kernel logical memory map

 [ffff600000000000	ffff7fffffffffff]	  32TB		[kasan shadow region]

  ffff800000000000	ffff80007fffffff	   2GB		modules

  ffff800080000000	fffffbffefffffff	 124TB		vmalloc

  fffffbfff0000000	fffffbfffdffffff	 224MB		fixed mappings (top down)

  fffffbfffe000000	fffffbfffe7fffff	   8MB		[guard region]

  fffffbfffe800000	fffffbffff7fffff	  16MB		PCI I/O space

  fffffbffff800000	fffffbffffffffff	   8MB		[guard region]

  fffffc0000000000	fffffdffffffffff	   2TB		vmemmap

  fffffe0000000000	ffffffffffffffff	   2TB		[guard region]





AArch64 Linux memory layout with 64KB pages + 3 levels (52-bit with HW support)::



  Start			End			Size		Use

  -----------------------------------------------------------------------

  0000000000000000	000fffffffffffff	   4PB		user

  fff0000000000000	ffff7fffffffffff	  ~4PB		kernel logical memory map

 [fffd800000000000	ffff7fffffffffff]	 512TB		[kasan shadow region]

  ffff800000000000	ffff80007fffffff	   2GB		modules

  ffff800080000000	fffffbffefffffff	 124TB		vmalloc

  fffffbfff0000000	fffffbfffdffffff	 224MB		fixed mappings (top down)

  fffffbfffe000000	fffffbfffe7fffff	   8MB		[guard region]

  fffffbfffe800000	fffffbffff7fffff	  16MB		PCI I/O space

  fffffbffff800000	fffffbffffffffff	   8MB		[guard region]

  fffffc0000000000	ffffffdfffffffff	  ~4TB		vmemmap

  ffffffe000000000	ffffffffffffffff	 128GB		[guard region]





Translation table lookup with 4KB pages::



  +--------+--------+--------+--------+--------+--------+--------+--------+

  |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|

  +--------+--------+--------+--------+--------+--------+--------+--------+

            |        |         |         |         |         |

            |        |         |         |         |         v

            |        |         |         |         |   [11:0]  in-page offset

            |        |         |         |         +-> [20:12] L3 index

            |        |         |         +-----------> [29:21] L2 index

            |        |         +---------------------> [38:30] L1 index

            |        +-------------------------------> [47:39] L0 index

            +----------------------------------------> [55] TTBR0/1





Translation table lookup with 64KB pages::



  +--------+--------+--------+--------+--------+--------+--------+--------+

  |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|

  +--------+--------+--------+--------+--------+--------+--------+--------+

            |        |    |               |              |

            |        |    |               |              v

            |        |    |               |            [15:0]  in-page offset

            |        |    |               +----------> [28:16] L3 index

            |        |    +--------------------------> [41:29] L2 index

            |        +-------------------------------> [47:42] L1 index (48-bit)

            |                                          [51:42] L1 index (52-bit)

            +----------------------------------------> [55] TTBR0/1





When using KVM without the Virtualization Host Extensions, the

hypervisor maps kernel pages in EL2 at a fixed (and potentially

random) offset from the linear mapping. See the kern_hyp_va macro and