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- .. SPDX-License-Identifier: GPL-2.0
- =====================================
- Virtual Memory Layout on RISC-V Linux
- =====================================
- :Author: Alexandre Ghiti <[email protected]>
- :Date: 12 February 2021
- This document describes the virtual memory layout used by the RISC-V Linux
- Kernel.
- 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 will
- occur.": that splits the virtual address space into 2 halves separated by a very
- big hole, the lower half is where the userspace resides, the upper half is where
- the 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:
- ____________________________________________________________|___________________________________________________________
- | | | |
- ffffffc6fea00000 | -228 GB | ffffffc6feffffff | 6 MB | fixmap
- ffffffc6ff000000 | -228 GB | ffffffc6ffffffff | 16 MB | PCI io
- ffffffc700000000 | -228 GB | ffffffc7ffffffff | 4 GB | vmemmap
- ffffffc800000000 | -224 GB | ffffffd7ffffffff | 64 GB | vmalloc/ioremap space
- ffffffd800000000 | -160 GB | fffffff6ffffffff | 124 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
- __________________|____________|__________________|_________|____________________________________________________________
|
