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
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| | |
+- 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