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kirylhansendc
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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@linux.intel.com> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Link: https://lore.kernel.org/all/20241031084946.2243440-1-kirill.shutemov%40linux.intel.com
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‎Documentation/arch/x86/x86_64/mm.rst

Lines changed: 29 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -29,15 +29,27 @@ Complete virtual memory map with 4-level page tables
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Start addr | Offset | End addr | Size | VM area description
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========================================================================================================================
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| | | |
32-
0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm
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0000000000000000 | 0 | 00007fffffffefff | ~128 TB | user-space virtual memory, different per mm
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00007ffffffff000 | ~128 TB | 00007fffffffffff | 4 kB | ... guard hole
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__________________|____________|__________________|_________|___________________________________________________________
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| | | |
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0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -128 TB
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0000800000000000 | +128 TB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -8 EB
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| | | | starting offset of kernel mappings.
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| | | |
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| | | | LAM relaxes canonicallity check allowing to create aliases
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| | | | for userspace memory here.
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__________________|____________|__________________|_________|___________________________________________________________
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|
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| Kernel-space virtual memory, shared between all processes:
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__________________|____________|__________________|_________|___________________________________________________________
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| | | |
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8000000000000000 | -8 EB | ffff7fffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -128 TB
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| | | | starting offset of kernel mappings.
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| | | |
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| | | | LAM_SUP relaxes canonicallity check allowing to create
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| | | | aliases for kernel memory here.
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____________________________________________________________|___________________________________________________________
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| | | |
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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
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Start addr | Offset | End addr | Size | VM area description
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========================================================================================================================
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| | | |
91-
0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm
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0000000000000000 | 0 | 00fffffffffff000 | ~64 PB | user-space virtual memory, different per mm
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00fffffffffff000 | ~64 PB | 00ffffffffffffff | 4 kB | ... guard hole
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__________________|____________|__________________|_________|___________________________________________________________
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| | | |
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0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, still almost 64 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -64 PB
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0100000000000000 | +64 PB | 7fffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -8EB TB
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| | | | starting offset of kernel mappings.
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| | | |
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| | | | LAM relaxes canonicallity check allowing to create aliases
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| | | | for userspace memory here.
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__________________|____________|__________________|_________|___________________________________________________________
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|
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| Kernel-space virtual memory, shared between all processes:
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____________________________________________________________|___________________________________________________________
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8000000000000000 | -8 EB | feffffffffffffff | ~8 EB | ... huge, almost 63 bits wide hole of non-canonical
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| | | | virtual memory addresses up to the -64 PB
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| | | | starting offset of kernel mappings.
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| | | |
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| | | | LAM_SUP relaxes canonicallity check allowing to create
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| | | | aliases for kernel memory here.
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____________________________________________________________|___________________________________________________________
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| | | |
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ff00000000000000 | -64 PB | ff0fffffffffffff | 4 PB | ... guard hole, also reserved for hypervisor

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