Re: [PATCH v6 4/9] xen/riscv: set up fixmap mappings

[Jan Beulich <jbeulich@suse.com>]

On 02.09.2024 19:01, Oleksii Kurochko wrote:
> Set up fixmap mappings and the L0 page table for fixmap support.
> 
> Modify the Page Table Entries (PTEs) directly in arch_pmap_map()
> instead of using set_fixmap() ( which relies on map_pages_to_xen() ).

What do you derive this from? There's no set_fixmap() here, and hence
it's unknown how it is going to be implemented. The most you can claim
is that it is expected that it will use map_pages_to_xen(), which in
turn ...

> This change is necessary because PMAP is used when the domain map
> page infrastructure is not yet initialized so map_pages_to_xen()
> called by set_fixmap() needs to map pages on demand, which then
> calls pmap() again, resulting in a loop.

... is only expected to use arch_pmap_map().

> @@ -81,6 +82,18 @@ static inline void flush_page_to_ram(unsigned long mfn, bool sync_icache)
>      BUG_ON("unimplemented");
>  }
>  
> +/* Write a pagetable entry. */
> +static inline void write_pte(pte_t *p, pte_t pte)
> +{
> +    write_atomic(p, pte);
> +}
> +
> +/* Read a pagetable entry. */
> +static inline pte_t read_pte(pte_t *p)

const pte_t *?

Jan