Re: [PATCH 2/7] RISC-V: doc: Add file describing the virtual memory map

[Mike Rapoport <rppt@linux.ibm.com>]

Hi,

On Wed, Mar 27, 2019 at 03:36:38PM -0600, Logan Gunthorpe wrote:
> 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.

Please move the text before the tables, so that meaning of Sv32 and Sv39
would be clear.

> -- 
> 2.20.1
> 
> 
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> 

-- 
Sincerely yours,
Mike.


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