Re: [RFC V1 14/16] arm64/mm: Enable fixmap with 5 level page table

David Hildenbrand (Arm)
2026-04-15T10:39:25Z

On 4/10/26 05:22, Anshuman Khandual wrote:
>
>
> On 08/04/26 5:59 PM, David Hildenbrand (Arm) wrote:
>> On 2/24/26 06:11, Anshuman Khandual wrote:
>>> Enable fixmap with 5 level page table when required. This creates table
>>> entries at the PGD level. Add a fallback stub for pgd_page_paddr() when
>>> (PGTBALE_LEVELS <= 4) which helps in intercepting any unintended usage.
>>
>> Can you add the "why" ?
>
> Following reworded commit message should work ?
>
> ------------------------------------------------------------------
> arm64/mm: Enable fixmap with 5 level page table
>
> FEAT_D128 halves PTRS_PER_PXX thus shrinking the VA range coverage
> for each page table level. Hence in order to preserve all existing
> VA range configurations, some geometry now need to become 5-level.
>
> Since fixmap is used to build and manipulate page tables early on
> during boot the mapping must also gain that additional level which
> was not required earlier.
>
> Enable fixmap with 5 level page table when required. This creates table
> entries at the PGD level. Add a fallback stub for pgd_page_paddr() when
> (PGTBALE_LEVELS <= 4) which helps in intercepting any unintended usage.
> -------------------------------------------------------------------

Perfect, thanks!

--
Cheers,

David