mm.rst

  1.. SPDX-License-Identifier: GPL-2.0
  2
  3=================
  4Memory Management
  5=================
  6
  7Virtual memory layout
  8=====================
  9
 10.. note::
 11
 12 - Some aspects of the virtual memory layout setup are not
 13   clarified (number of page levels, alignment, DMA memory).
 14
 15 - Unused gaps in the virtual memory layout could be present
 16   or not - depending on how partucular system is configured.
 17   No page tables are created for the unused gaps.
 18
 19 - The virtual memory regions are tracked or untracked by KASAN
 20   instrumentation, as well as the KASAN shadow memory itself is
 21   created only when CONFIG_KASAN configuration option is enabled.
 22
 23::
 24
 25  =============================================================================
 26  |    Physical      |	  Virtual	| VM area description
 27  =============================================================================
 28  +- 0 --------------+- 0 --------------+
 29  |		     | S390_lowcore	| Low-address memory
 30  |		     +- 8 KB -----------+
 31  |		     |			|
 32  |		     |			|
 33  |		     | ... unused gap	| KASAN untracked
 34  |		     |			|
 35  +- AMODE31_START --+- AMODE31_START --+ .amode31 rand. phys/virt start
 36  |.amode31 text/data|.amode31 text/data| KASAN untracked
 37  +- AMODE31_END ----+- AMODE31_END ----+ .amode31 rand. phys/virt end (<2GB)
 38  |		     |			|
 39  |		     |			|
 40  +- __kaslr_offset_phys		| kernel rand. phys start
 41  |		     |			|
 42  | kernel text/data |			|
 43  |		     |			|
 44  +------------------+			| kernel phys end
 45  |		     |			|
 46  |		     |			|
 47  |		     |			|
 48  |		     |			|
 49  +- ident_map_size -+			|
 50		     |			|
 51		     |	... unused gap	| KASAN untracked
 52		     |			|
 53		     +- __identity_base + identity mapping start (>= 2GB)
 54		     |			|
 55		     | identity		| phys == virt - __identity_base
 56		     | mapping		| virt == phys + __identity_base
 57		     |			|
 58		     |			| KASAN tracked
 59		     |			|
 60		     |			|
 61		     |			|
 62		     |			|
 63		     |			|
 64		     |			|
 65		     |			|
 66		     |			|
 67		     |			|
 68		     |			|
 69		     |			|
 70		     |			|
 71		     |			|
 72		     |			|
 73		     |			|
 74		     +---- vmemmap -----+ 'struct page' array start
 75		     |			|
 76		     | virtually mapped |
 77		     | memory map	| KASAN untracked
 78		     |			|
 79		     +- __abs_lowcore --+
 80		     |			|
 81		     | Absolute Lowcore | KASAN untracked
 82		     |			|
 83		     +- __memcpy_real_area
 84		     |			|
 85		     |	Real Memory Copy| KASAN untracked
 86		     |			|
 87		     +- VMALLOC_START --+ vmalloc area start
 88		     |			| KASAN untracked or
 89		     |	vmalloc area	| KASAN shallowly populated in case
 90		     |			|	CONFIG_KASAN_VMALLOC=y
 91		     +- MODULES_VADDR --+ modules area start
 92		     |			| KASAN allocated per module or
 93		     |	modules area	| KASAN shallowly populated in case
 94		     |			|	CONFIG_KASAN_VMALLOC=y
 95		     +- __kaslr_offset -+ kernel rand. virt start
 96		     |			| KASAN tracked
 97		     | kernel text/data | phys == (kvirt - __kaslr_offset) +
 98		     |			|	  __kaslr_offset_phys
 99		     +- kernel .bss end + kernel rand. virt end
100		     |			|
101		     |	... unused gap	| KASAN untracked
102		     |			|
103		     +------------------+ UltraVisor Secure Storage limit
104		     |			|
105		     |	... unused gap	| KASAN untracked
106		     |			|
107		     +KASAN_SHADOW_START+ KASAN shadow memory start
108		     |			|
109		     |	 KASAN shadow	| KASAN untracked
110		     |			|
111		     +------------------+ ASCE limit