__  __    __   __  _____      _            _          _____ _          _ _ 
 |  \/  |   \ \ / / |  __ \    (_)          | |        / ____| |        | | |
 | \  / |_ __\ V /  | |__) | __ ___   ____ _| |_ ___  | (___ | |__   ___| | |
 | |\/| | '__|> <   |  ___/ '__| \ \ / / _` | __/ _ \  \___ \| '_ \ / _ \ | |
 | |  | | |_ / . \  | |   | |  | |\ V / (_| | ||  __/  ____) | | | |  __/ | |
 |_|  |_|_(_)_/ \_\ |_|   |_|  |_| \_/ \__,_|\__\___| |_____/|_| |_|\___V 2.1
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<section id="memory-management">
<h1>Memory Management<a class="headerlink" href="#memory-management" title="Link to this heading">¶</a></h1>
<section id="virtual-memory-layout">
<h2>Virtual memory layout<a class="headerlink" href="#virtual-memory-layout" title="Link to this heading">¶</a></h2>
<div class="admonition note">
<p class="admonition-title">Note</p>
<ul class="simple">
<li><p>Some aspects of the virtual memory layout setup are not
clarified (number of page levels, alignment, DMA memory).</p></li>
<li><p>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.</p></li>
<li><p>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.</p></li>
</ul>
</div>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>=============================================================================
|    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 (&lt;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 (&gt;= 2GB)
                   |                  |
                   | identity         | phys == virt - __identity_base
                   | mapping          | virt == phys + __identity_base
                   |                  |
                   |                  | KASAN tracked
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   |                  |
                   +---- vmemmap -----+ &#39;struct page&#39; 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
</pre></div>
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