Documentation/arch/arm64/ptdump.rst

Source file repositories/reference/linux-study-clean/Documentation/arch/arm64/ptdump.rst

File Facts

System: Linux kernel
Corpus path: Documentation/arch/arm64/ptdump.rst
Extension: .rst
Size: 6365 bytes
Lines: 95
Domain: Support Tooling And Documentation
Bucket: Documentation
Inferred role: Support Tooling And Documentation: documentation
Status: atlas-only

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.
Allocates kernel memory; connect allocation flags and lifetime to context constraints.

Dependency Surface

No C-style include directives detected by the generator.

Detected Declarations

No top-level syscall, struct, function, initcall, or export declaration detected by the generator.

Annotated Snippet

======================
Kernel page table dump
======================

ptdump is a debugfs interface that provides a detailed dump of the
kernel page tables. It offers a comprehensive overview of the kernel
virtual memory layout as well as the attributes associated with the
various regions in a human-readable format. It is useful to dump the
kernel page tables to verify permissions and memory types. Examining the
page table entries and permissions helps identify potential security
vulnerabilities such as mappings with overly permissive access rights or
improper memory protections.

Memory hotplug allows dynamic expansion or contraction of available
memory without requiring a system reboot. To maintain the consistency
and integrity of the memory management data structures, arm64 makes use
of the ``mem_hotplug_lock`` semaphore in write mode. Additionally, in
read mode, ``mem_hotplug_lock`` supports an efficient implementation of
``get_online_mems()`` and ``put_online_mems()``. These protect the
offlining of memory being accessed by the ptdump code.

In order to dump the kernel page tables, enable the following
configurations and mount debugfs::

 CONFIG_PTDUMP_DEBUGFS=y

 mount -t debugfs nodev /sys/kernel/debug
 cat /sys/kernel/debug/kernel_page_tables

On analysing the output of ``cat /sys/kernel/debug/kernel_page_tables``
one can derive information about the virtual address range of the entry,
followed by size of the memory region covered by this entry, the
hierarchical structure of the page tables and finally the attributes
associated with each page. The page attributes provide information about
access permissions, execution capability, type of mapping such as leaf
level PTE or block level PGD, PMD and PUD, and access status of a page
within the kernel memory. Assessing these attributes can assist in
understanding the memory layout, access patterns and security
characteristics of the kernel pages.

Kernel virtual memory layout example::

 start address        end address         size             attributes
 +---------------------------------------------------------------------------------------+
 | ---[ Linear Mapping start ]---------------------------------------------------------- |
 | ..................                                                                    |
 | 0xfff0000000000000-0xfff0000000210000  2112K PTE RW NX SHD AF  UXN  MEM/NORMAL-TAGGED |
 | 0xfff0000000210000-0xfff0000001c00000 26560K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
 | ..................                                                                    |
 | ---[ Linear Mapping end ]------------------------------------------------------------ |
 +---------------------------------------------------------------------------------------+
 | ---[ Modules start ]----------------------------------------------------------------- |
 | ..................                                                                    |
 | 0xffff800000000000-0xffff800008000000   128M PTE                                      |
 | ..................                                                                    |
 | ---[ Modules end ]------------------------------------------------------------------- |
 +---------------------------------------------------------------------------------------+
 | ---[ vmalloc() area ]---------------------------------------------------------------- |
 | ..................                                                                    |
 | 0xffff800008010000-0xffff800008200000  1984K PTE ro x  SHD AF       UXN  MEM/NORMAL   |
 | 0xffff800008200000-0xffff800008e00000    12M PTE ro x  SHD AF  CON  UXN  MEM/NORMAL   |
 | ..................                                                                    |
 | ---[ vmalloc() end ]----------------------------------------------------------------- |
 +---------------------------------------------------------------------------------------+
 | ---[ Fixmap start ]------------------------------------------------------------------ |
 | ..................                                                                    |
 | 0xfffffbfffdb80000-0xfffffbfffdb90000    64K PTE ro x  SHD AF  UXN  MEM/NORMAL        |
 | 0xfffffbfffdb90000-0xfffffbfffdba0000    64K PTE ro NX SHD AF  UXN  MEM/NORMAL        |
 | ..................                                                                    |
 | ---[ Fixmap end ]-------------------------------------------------------------------- |

Annotation

Atlas domain: Support Tooling And Documentation / Documentation.
Implementation status: atlas-only.

Implementation Notes

This generated page is the file-by-file coverage layer; curated subsystem chapters should link here when they synthesize a multi-file control flow.
Core OS pages should be promoted from atlas-only to deep-reviewed when they explain data structures, invariants, locking, lifecycle, and C implementation snippets.
Driver-family pages are intentionally pattern-oriented unless they are part of the selected PCIe/NVMe representative device path.