linux-kernel - Re: [PATCH] docs: arm64: update memory layout for vmemmap region

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Message-ID: <20250108135748.GA9367@willie-the-truck>
Date: Wed, 8 Jan 2025 13:57:48 +0000
From: Will Deacon <will@...nel.org>
To: Sangmoon Kim <sangmoon.kim@...sung.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Jonathan Corbet <corbet@....net>,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, ardb@...nel.org
Subject: Re: [PATCH] docs: arm64: update memory layout for vmemmap region

On Thu, Jan 02, 2025 at 03:52:37PM +0900, Sangmoon Kim wrote:
> Commit 031e011d8b22 ("arm64: mm: Move PCI I/O emulation region above
> the vmemmap region") and commit b730b0f2b1fc ("arm64: mm: Move fixmap
> region above vmemmap region") have placed PCI I/O and fixmap region
> above vmemmap region.
> 
> And commit 32697ff38287 ("arm64: vmemmap: Avoid base2 order of struct
> page size to dimension region") has moved vmemmap region to higher
> address.
> 
> Update document as the memory layout modified by the previous patches.
> 
> Signed-off-by: Sangmoon Kim <sangmoon.kim@...sung.com>
> ---
>  Documentation/arch/arm64/memory.rst | 28 ++++++++++++++--------------
>  1 file changed, 14 insertions(+), 14 deletions(-)

To be honest with you, this document is pretty stale (it doesn't even
mention 16k pages) and almost impossible to keep in-sync with the code.
I'd be inclined to remove these tables; we have ptdump support if people
really want to see where things are.

Will

--->8

diff --git a/Documentation/arch/arm64/memory.rst b/Documentation/arch/arm64/memory.rst
index 8a658984b8bb..678fbb418c3a 100644
--- a/Documentation/arch/arm64/memory.rst
+++ b/Documentation/arch/arm64/memory.rst
@@ -23,71 +23,6 @@ swapper_pg_dir contains only kernel (global) mappings while the user pgd
 contains only user (non-global) mappings.  The swapper_pg_dir address is
 written to TTBR1 and never written to TTBR0.
 
-
-AArch64 Linux memory layout with 4KB pages + 4 levels (48-bit)::
-
-  Start			End			Size		Use
-  -----------------------------------------------------------------------
-  0000000000000000	0000ffffffffffff	 256TB		user
-  ffff000000000000	ffff7fffffffffff	 128TB		kernel logical memory map
- [ffff600000000000	ffff7fffffffffff]	  32TB		[kasan shadow region]
-  ffff800000000000	ffff80007fffffff	   2GB		modules
-  ffff800080000000	fffffbffefffffff	 124TB		vmalloc
-  fffffbfff0000000	fffffbfffdffffff	 224MB		fixed mappings (top down)
-  fffffbfffe000000	fffffbfffe7fffff	   8MB		[guard region]
-  fffffbfffe800000	fffffbffff7fffff	  16MB		PCI I/O space
-  fffffbffff800000	fffffbffffffffff	   8MB		[guard region]
-  fffffc0000000000	fffffdffffffffff	   2TB		vmemmap
-  fffffe0000000000	ffffffffffffffff	   2TB		[guard region]
-
-
-AArch64 Linux memory layout with 64KB pages + 3 levels (52-bit with HW support)::
-
-  Start			End			Size		Use
-  -----------------------------------------------------------------------
-  0000000000000000	000fffffffffffff	   4PB		user
-  fff0000000000000	ffff7fffffffffff	  ~4PB		kernel logical memory map
- [fffd800000000000	ffff7fffffffffff]	 512TB		[kasan shadow region]
-  ffff800000000000	ffff80007fffffff	   2GB		modules
-  ffff800080000000	fffffbffefffffff	 124TB		vmalloc
-  fffffbfff0000000	fffffbfffdffffff	 224MB		fixed mappings (top down)
-  fffffbfffe000000	fffffbfffe7fffff	   8MB		[guard region]
-  fffffbfffe800000	fffffbffff7fffff	  16MB		PCI I/O space
-  fffffbffff800000	fffffbffffffffff	   8MB		[guard region]
-  fffffc0000000000	ffffffdfffffffff	  ~4TB		vmemmap
-  ffffffe000000000	ffffffffffffffff	 128GB		[guard region]
-
-
-Translation table lookup with 4KB pages::
-
-  +--------+--------+--------+--------+--------+--------+--------+--------+
-  |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
-  +--------+--------+--------+--------+--------+--------+--------+--------+
-            |        |         |         |         |         |
-            |        |         |         |         |         v
-            |        |         |         |         |   [11:0]  in-page offset
-            |        |         |         |         +-> [20:12] L3 index
-            |        |         |         +-----------> [29:21] L2 index
-            |        |         +---------------------> [38:30] L1 index
-            |        +-------------------------------> [47:39] L0 index
-            +----------------------------------------> [55] TTBR0/1
-
-
-Translation table lookup with 64KB pages::
-
-  +--------+--------+--------+--------+--------+--------+--------+--------+
-  |63    56|55    48|47    40|39    32|31    24|23    16|15     8|7      0|
-  +--------+--------+--------+--------+--------+--------+--------+--------+
-            |        |    |               |              |
-            |        |    |               |              v
-            |        |    |               |            [15:0]  in-page offset
-            |        |    |               +----------> [28:16] L3 index
-            |        |    +--------------------------> [41:29] L2 index
-            |        +-------------------------------> [47:42] L1 index (48-bit)
-            |                                          [51:42] L1 index (52-bit)
-            +----------------------------------------> [55] TTBR0/1
-
-
 When using KVM without the Virtualization Host Extensions, the
 hypervisor maps kernel pages in EL2 at a fixed (and potentially
 random) offset from the linear mapping. See the kern_hyp_va macro and