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diff --git a/Documentation/arch/s390/mm.rst b/Documentation/arch/s390/mm.rst new file mode 100644 index 000000000000..084adad5eef9 --- /dev/null +++ b/Documentation/arch/s390/mm.rst @@ -0,0 +1,111 @@ +.. 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 |