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Virtual Memory Layout on RISC-V Linux¶
- Author:
Alexandre Ghiti <alex@ghiti.fr>
- Date:
12 February 2021
This document describes the virtual memory layout used by the RISC-V LinuxKernel.
RISC-V Linux Kernel 32bit¶
RISC-V Linux Kernel SV32¶
TODO
RISC-V Linux Kernel 64bit¶
The RISC-V privileged architecture document states that the 64bit addresses“must have bits 63–48 all equal to bit 47, or else a page-fault exception willoccur.”: that splits the virtual address space into 2 halves separated by a verybig hole, the lower half is where the userspace resides, the upper half is wherethe RISC-V Linux Kernel resides.
RISC-V Linux Kernel SV39¶
======================================================================================================================== Start addr | Offset | End addr | Size | VM area description======================================================================================================================== | | | | 0000000000000000 | 0 | 0000003fffffffff | 256 GB | user-space virtual memory, different per mm__________________|____________|__________________|_________|___________________________________________________________ | | | | 0000004000000000 | +256 GB | ffffffbfffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical | | | | virtual memory addresses up to the -256 GB | | | | starting offset of kernel mappings.__________________|____________|__________________|_________|___________________________________________________________ | | Kernel-space virtual memory, shared between all processes:____________________________________________________________|___________________________________________________________ | | | | ffffffc4fea00000 | -236 GB | ffffffc4feffffff | 6 MB | fixmap ffffffc4ff000000 | -236 GB | ffffffc4ffffffff | 16 MB | PCI io ffffffc500000000 | -236 GB | ffffffc5ffffffff | 4 GB | vmemmap ffffffc600000000 | -232 GB | ffffffd5ffffffff | 64 GB | vmalloc/ioremap space ffffffd600000000 | -168 GB | fffffff5ffffffff | 128 GB | direct mapping of all physical memory | | | | fffffff700000000 | -36 GB | fffffffeffffffff | 32 GB | kasan__________________|____________|__________________|_________|____________________________________________________________ | |____________________________________________________________|____________________________________________________________ | | | | ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel__________________|____________|__________________|_________|____________________________________________________________
RISC-V Linux Kernel SV48¶
======================================================================================================================== Start addr | Offset | End addr | Size | VM area description======================================================================================================================== | | | | 0000000000000000 | 0 | 00007fffffffffff | 128 TB | user-space virtual memory, different per mm __________________|____________|__________________|_________|___________________________________________________________ | | | | 0000800000000000 | +128 TB | ffff7fffffffffff | ~16M TB | ... huge, almost 64 bits wide hole of non-canonical | | | | virtual memory addresses up to the -128 TB | | | | starting offset of kernel mappings. __________________|____________|__________________|_________|___________________________________________________________ | | Kernel-space virtual memory, shared between all processes: ____________________________________________________________|___________________________________________________________ | | | | ffff8d7ffea00000 | -114.5 TB | ffff8d7ffeffffff | 6 MB | fixmap ffff8d7fff000000 | -114.5 TB | ffff8d7fffffffff | 16 MB | PCI io ffff8d8000000000 | -114.5 TB | ffff8f7fffffffff | 2 TB | vmemmap ffff8f8000000000 | -112.5 TB | ffffaf7fffffffff | 32 TB | vmalloc/ioremap space ffffaf8000000000 | -80.5 TB | ffffef7fffffffff | 64 TB | direct mapping of all physical memory ffffef8000000000 | -16.5 TB | fffffffeffffffff | 16.5 TB | kasan __________________|____________|__________________|_________|____________________________________________________________ | | Identical layout to the 39-bit one from here on: ____________________________________________________________|____________________________________________________________ | | | | ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|____________________________________________________________
RISC-V Linux Kernel SV57¶
======================================================================================================================== Start addr | Offset | End addr | Size | VM area description======================================================================================================================== | | | | 0000000000000000 | 0 | 00ffffffffffffff | 64 PB | user-space virtual memory, different per mm __________________|____________|__________________|_________|___________________________________________________________ | | | | 0100000000000000 | +64 PB | feffffffffffffff | ~16K PB | ... huge, almost 64 bits wide hole of non-canonical | | | | virtual memory addresses up to the -64 PB | | | | starting offset of kernel mappings. __________________|____________|__________________|_________|___________________________________________________________ | | Kernel-space virtual memory, shared between all processes: ____________________________________________________________|___________________________________________________________ | | | | ff1bfffffea00000 | -57 PB | ff1bfffffeffffff | 6 MB | fixmap ff1bffffff000000 | -57 PB | ff1bffffffffffff | 16 MB | PCI io ff1c000000000000 | -57 PB | ff1fffffffffffff | 1 PB | vmemmap ff20000000000000 | -56 PB | ff5fffffffffffff | 16 PB | vmalloc/ioremap space ff60000000000000 | -40 PB | ffdeffffffffffff | 32 PB | direct mapping of all physical memory ffdf000000000000 | -8 PB | fffffffeffffffff | 8 PB | kasan __________________|____________|__________________|_________|____________________________________________________________ | | Identical layout to the 39-bit one from here on: ____________________________________________________________|____________________________________________________________ | | | | ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|____________________________________________________________