Re: [PATCH v6 11/19] xen/riscv: implement p2m_set_range()

[Jan Beulich <jbeulich@xxxxxxxx>]

On 24.11.2025 13:33, Oleksii Kurochko wrote:
> @@ -28,6 +36,77 @@ unsigned char get_max_supported_mode(void)
>      return max_gstage_mode.mode;
>  }
>  
> +static inline unsigned int calc_offset(const struct p2m_domain *p2m,
> +                                       const unsigned int lvl,
> +                                       const paddr_t gpa)
> +{
> +    unsigned int off = (gpa >> P2M_GFN_LEVEL_SHIFT(lvl)) &
> +                       P2M_TABLE_OFFSET(p2m, lvl);
> +
> +    /*
> +     * For P2M_ROOT_LEVEL, `offset` ranges from 0 to 2047, since the root
> +     * page table spans 4 consecutive 4KB pages.
> +     * We want to return an index within one of these 4 pages.
> +     * The specific page to use is determined by `p2m_get_root_pointer()`.
> +     *
> +     * Example: if `offset == 512`:
> +     *  - A single 4KB page holds 512 entries.
> +     *  - Therefore, entry 512 corresponds to index 0 of the second page.
> +     *
> +     * At all other levels, only one page is allocated, and `offset` is
> +     * always in the range 0 to 511, since the VPN is 9 bits long.
> +     */
> +    return off & (PAGETABLE_ENTRIES - 1);
> +}
> +
> +#define P2M_MAX_ROOT_LEVEL 5
> +
> +#define P2M_BUILD_LEVEL_OFFSETS(p2m, var, addr) \
> +    unsigned int var[P2M_MAX_ROOT_LEVEL] = {-1}; \

What use is this initializer? Slot 0 ...

> +    BUG_ON(P2M_ROOT_LEVEL(p2m) >= P2M_MAX_ROOT_LEVEL); \
> +    for ( unsigned int i = 0; i <= P2M_ROOT_LEVEL(p2m); i++ ) \
> +        var[i] = calc_offset(p2m, i, addr);

... is guaranteed to be written to, afaics. With this simplified (or an
explanation given for why it is needed)
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan