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+.. 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
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ | |
+ +---- 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