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    Subject[PATCH 2/7] RISC-V: doc: Add file describing the virtual memory map
    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 <logang@deltatee.com>
    Cc: Jonathan Corbet <corbet@lwn.net>
    Cc: Palmer Dabbelt <palmer@sifive.com>
    Cc: Albert Ou <aou@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
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