.. SPDX-License-Identifier: GPL-2.0 ===================================== Virtual Memory Layout on RISC-V Linux ===================================== :Author: Alexandre Ghiti :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: ____________________________________________________________|___________________________________________________________ | | | | ffffffc000000000 | -256 GB | ffffffc7ffffffff | 32 GB | kasan ffffffcefee00000 | -196 GB | ffffffcefeffffff | 2 MB | fixmap ffffffceff000000 | -196 GB | ffffffceffffffff | 16 MB | PCI io ffffffcf00000000 | -196 GB | ffffffcfffffffff | 4 GB | vmemmap ffffffd000000000 | -192 GB | ffffffdfffffffff | 64 GB | vmalloc/ioremap space ffffffe000000000 | -128 GB | ffffffff7fffffff | 124 GB | direct mapping of all physical memory __________________|____________|__________________|_________|____________________________________________________________ | | ____________________________________________________________|____________________________________________________________ | | | | ffffffff00000000 | -4 GB | ffffffff7fffffff | 2 GB | modules, BPF ffffffff80000000 | -2 GB | ffffffffffffffff | 2 GB | kernel __________________|____________|__________________|_________|____________________________________________________________