This file is similar to the x86_64 equivalent (in Documentation/x86/x86_64/mm.txt) and describes the virtuas address space usage for RISC-V.
Signed-off-by: Logan Gunthorpe <log...@deltatee.com> Cc: Jonathan Corbet <cor...@lwn.net> Cc: Palmer Dabbelt <pal...@sifive.com> Cc: Albert Ou <a...@eecs.berkeley.edu> --- Documentation/riscv/mm.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100644 Documentation/riscv/mm.txt diff --git a/Documentation/riscv/mm.txt b/Documentation/riscv/mm.txt new file mode 100644 index 000000000000..725dc85f2c65 --- /dev/null +++ b/Documentation/riscv/mm.txt @@ -0,0 +1,24 @@ +Sv32: + +00000000 - 7fffffff user space, different per mm (2G) +80000000 - 81ffffff virtual memory map (32MB) +82000000 - bfffffff vmalloc/ioremap space (1GB - 32MB) +c0000000 - ffffffff direct mapping of lower phys. memory (1GB) + +Sv39: + +0000000000000000 - 0000003fffffffff user space, different per mm (256GB) +hole caused by [38:63] sign extension +ffffffc000000000 - ffffffc0ffffffff virtual memory map (4GB) +ffffffc100000000 - ffffffd0ffffffff vmalloc/ioremap spac (64GB) +ffffffd100000000 - ffffffffffffffff linear mapping of physical space (188GB) + ffffffd200000000 - 0xfffffff200000000 linear mapping of all physical memory + +The RISC-V architecture defines virtual address bits in multiples of nine +starting from 39. These are referred to as Sv39, Sv48, Sv57 and Sv64. +Currently only Sv39 is supported. Bits 63 through to the most-significant +implemented bit are sign extended. This causes a hole between user space +and kernel addresses if you interpret them as unsigned. + +The direct mapping covers as much of the physical memory space as +possible so that it may cover some IO memory. -- 2.20.1
