Re: [PATCH v7 1/5] xen/riscv: add VM space layout

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.05.2023 19:09, 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 SV39

I did point you at x86'es similar #ifdef. Unlike here, there we use a
symbol which actually has a meaning, allowing to spot this comment in
e.g. grep output when looking for uses of that symbol. Hence here e.g.

#ifdef RV_STAGE1_MODE == SATP_MODE_SV39

? (I would also recommend to use the same style as x86 does, such that
the #ifdef and #endif look like normal directives [e.g. again in grep
output], leaving aside that they're inside a comment.)

> + * 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 |  0000007f40000000 | 309 GB | L2 200-509 | Direct map

The upper bound here is 0000007f80000000 afaict, which then also makes
the earlier gap 1Gb in size.

Jan