Re: [PATCH v8 1/5] xen/riscv: add VM space layout

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.05.2023 14:18, Oleksii Kurochko wrote:
> --- a/xen/arch/riscv/include/asm/config.h
> +++ b/xen/arch/riscv/include/asm/config.h
> @@ -4,6 +4,42 @@
>  #include <xen/const.h>
>  #include <xen/page-size.h>
>  
> +/*
> + * RISC-V64 Layout:
> + *
> + * #ifdef RV_STAGE1_MODE == SATP_MODE_SV39

Nit: #if please, not #ifdef. Also may I stress again that ideally this
would be formatted such that when e.g. grep-ing for SATP_MODE_SV39, the
matching line here would _not_ give the impression of being "a comment
only" (making people possibly pay less attention)? My referral to the
x86 way of doing things remains.

> + * From the riscv-privileged doc:
> + *   When mapping between narrower and wider addresses,
> + *   RISC-V zero-extends a narrower physical address to a wider size.
> + *   The mapping between 64-bit virtual addresses and the 39-bit usable
> + *   address space of Sv39 is not based on zero-extension but instead
> + *   follows an entrenched convention that allows an OS to use one or
> + *   a few of the most-significant bits of a full-size (64-bit) virtual
> + *   address to quickly distinguish user and supervisor address regions.
> + *
> + * It means that:
> + *   top VA bits are simply ignored for the purpose of translating to PA.
> + *
> + * 
> ============================================================================
> + *    Start addr    |   End addr        |  Size  | Slot       |area 
> description
> + * 
> ============================================================================
> + * FFFFFFFFC0800000 |  FFFFFFFFFFFFFFFF |1016 MB | L2 511     | Unused
> + * FFFFFFFFC0600000 |  FFFFFFFFC0800000 |  2 MB  | L2 511     | Fixmap
> + * FFFFFFFFC0200000 |  FFFFFFFFC0600000 |  4 MB  | L2 511     | FDT
> + * FFFFFFFFC0000000 |  FFFFFFFFC0200000 |  2 MB  | L2 511     | Xen
> + *                 ...                  |  1 GB  | L2 510     | Unused
> + * 0000003200000000 |  0000007f80000000 | 309 GB | L2 200-509 | Direct map

And another, yet more minor nit: Would be nice if all addresses here
were spelled uniformly, i.e. also with upper vs lower case of hex
digit letter consistent.

Jan

> + *                 ...                  |  1 GB  | L2 199     | Unused
> + * 0000003100000000 |  00000031C0000000 |  3 GB  | L2 196-198 | Frametable
> + *                 ...                  |  1 GB  | L2 195     | Unused
> + * 0000003080000000 |  00000030C0000000 |  1 GB  | L2 194     | VMAP
> + *                 ...                  | 194 GB | L2 0 - 193 | Unused
> + * 
> ============================================================================
> + *
> + * #endif
> + */
> +
>  #if defined(CONFIG_RISCV_64)
>  # define LONG_BYTEORDER 3
>  # define ELFSIZE 64