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Message-ID: <20241031084946.2243440-1-kirill.shutemov@linux.intel.com>
Date: Thu, 31 Oct 2024 10:49:46 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] x86/mm/doc: Add missing details in virtual memory layout
Improve memory layout documentation:
- Document 4kB guard hole at the end of userspace.
See TASK_SIZE_MAX definition.
- Divide the description of the non-canonical hole into two parts:
userspace and kernel sides.
- Mention the effect of LAM on the non-canonical range.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
Documentation/arch/x86/x86_64/mm.rst | 35 +++++++++++++++++++++++-----
1 file changed, 29 insertions(+), 6 deletions(-)
diff --git a/Documentation/arch/x86/x86_64/mm.rst b/Documentation/arch/x86/x86_64/mm.rst
index 35e5e18c83d0..f2db178b353f 100644
--- a/Documentation/arch/x86/x86_64/mm.rst
+++ b/Documentation/arch/x86/x86_64/mm.rst
@@ -29,15 +29,27 @@ Complete virtual memory map with 4-level page tables
Start addr | Offset | End addr | Size | VM area description
========================================================================================================================
| | | |
- 0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm
+ 0000000000000000 | 0 | 00007fffffffefff | ~128 TB | user-space virtual memory, different per mm
+ 00007ffffffff000 | ~128 TB | 00007fffffffffff | 4 kB | ... guard hole
__________________|____________|__________________|_________|___________________________________________________________
| | | |
- 0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
- | | | | virtual memory addresses up to the -128 TB
+ 0000800000000000 | +128 TB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
+ | | | | virtual memory addresses up to the -8 EB
| | | | starting offset of kernel mappings.
+ | | | |
+ | | | | LAM relaxes canonicallity check allowing to create aliases
+ | | | | for userspace memory here.
__________________|____________|__________________|_________|___________________________________________________________
|
| Kernel-space virtual memory, shared between all processes:
+ __________________|____________|__________________|_________|___________________________________________________________
+ | | | |
+ 8000000000000000 | -8 EB | ffff7fffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
+ | | | | virtual memory addresses up to the -128 TB
+ | | | | starting offset of kernel mappings.
+ | | | |
+ | | | | LAM_SUP relaxes canonicallity check allowing to create
+ | | | | aliases for kernel memory here.
____________________________________________________________|___________________________________________________________
| | | |
ffff800000000000 | -128 TB | ffff87ffffffffff | 8 TB | ... guard hole, also reserved for hypervisor
@@ -88,15 +100,26 @@ Complete virtual memory map with 5-level page tables
Start addr | Offset | End addr | Size | VM area description
========================================================================================================================
| | | |
- 0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm
+ 0000000000000000 | 0 | 00fffffffffff000 | ~64 PB | user-space virtual memory, different per mm
+ 00fffffffffff000 | ~64 PB | 00ffffffffffffff | 4 kB | ... guard hole
__________________|____________|__________________|_________|___________________________________________________________
| | | |
- 0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, still almost 64 bits wide hole of non-canonical
- | | | | virtual memory addresses up to the -64 PB
+ 0100000000000000 | +64 PB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
+ | | | | virtual memory addresses up to the -8EB TB
| | | | starting offset of kernel mappings.
+ | | | |
+ | | | | LAM relaxes canonicallity check allowing to create aliases
+ | | | | for userspace memory here.
__________________|____________|__________________|_________|___________________________________________________________
|
| Kernel-space virtual memory, shared between all processes:
+ ____________________________________________________________|___________________________________________________________
+ 8000000000000000 | -8 EB | feffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
+ | | | | virtual memory addresses up to the -64 PB
+ | | | | starting offset of kernel mappings.
+ | | | |
+ | | | | LAM_SUP relaxes canonicallity check allowing to create
+ | | | | aliases for kernel memory here.
____________________________________________________________|___________________________________________________________
| | | |
ff00000000000000 | -64 PB | ff0fffffffffffff | 4 PB | ... guard hole, also reserved for hypervisor
--
2.45.2
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