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

[Anshuman Khandual]

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 ?

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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.
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