.. SPDX-License-Identifier: GPL-2.0
=================
Memory Management
=================
Virtual memory layout
=====================
.. note::
- Some aspects of the virtual memory layout setup are not
clarified (number of page levels, alignment, DMA memory).
- Unused gaps in the virtual memory layout could be present
or not - depending on how partucular system is configured.
No page tables are created for the unused gaps.
- The virtual memory regions are tracked or untracked by KASAN
instrumentation, as well as the KASAN shadow memory itself is
created only when CONFIG_KASAN configuration option is enabled.
::
=============================================================================
| Physical | Virtual | VM area description
=============================================================================
+- 0 --------------+- 0 --------------+
| | S390_lowcore | Low-address memory
| +- 8 KB -----------+
| | |
| | |
| | ... unused gap | KASAN untracked
| | |
+- AMODE31_START --+- AMODE31_START --+ .amode31 rand. phys/virt start
|.amode31 text/data|.amode31 text/data| KASAN untracked
+- AMODE31_END ----+- AMODE31_END ----+ .amode31 rand. phys/virt end (<2GB)
| | |
| | |
+- __kaslr_offset_phys | kernel rand. phys start
| | |
| kernel text/data | |
| | |
+------------------+ | kernel phys end
| | |
| | |
| | |
| | |
+- ident_map_size -+ |
| |
| ... unused gap | KASAN untracked
| |
+- __identity_base + identity mapping start (>= 2GB)
| |
| identity | phys == virt - __identity_base
| mapping | virt == phys + __identity_base
| |
| | KASAN tracked
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
| |
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+---- vmemmap -----+ 'struct page' array start
| |
| virtually mapped |
| memory map | KASAN untracked
| |
+- __abs_lowcore --+
| |
| Absolute Lowcore | KASAN untracked
| |
+- __memcpy_real_area
| |
| Real Memory Copy| KASAN untracked
| |
+- VMALLOC_START --+ vmalloc area start
| | KASAN untracked or
| vmalloc area | KASAN shallowly populated in case
| | CONFIG_KASAN_VMALLOC=y
+- MODULES_VADDR --+ modules area start
| | KASAN allocated per module or
| modules area | KASAN shallowly populated in case
| | CONFIG_KASAN_VMALLOC=y
+- __kaslr_offset -+ kernel rand. virt start
| | KASAN tracked
| kernel text/data | phys == (kvirt - __kaslr_offset) +
| | __kaslr_offset_phys
+- kernel .bss end + kernel rand. virt end
| |
| ... unused gap | KASAN untracked
| |
+------------------+ UltraVisor Secure Storage limit
| |
| ... unused gap | KASAN untracked
| |
+KASAN_SHADOW_START+ KASAN shadow memory start
| |
| KASAN shadow | KASAN untracked
| |
+------------------+ ASCE limit
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