Re: [PATCH v3 07/26] x86/mm: introduce mm-local region

[Brendan Jackman]

On Sun Aug 2, 2026 at 5:27 PM BST, Mike Rapoport wrote:
...
>> +#if defined(CONFIG_MITIGATION_PAGE_TABLE_ISOLATION) && defined(CONFIG_X86_PAE)
>> +static inline pmd_t *pgd_to_pmd_walk(pgd_t *pgd, unsigned long va)
>
> There's very similar mm_find_pmd() in mm/rmap.c and I bet a bunch of other
> places walk from PGD to PMD and return PMD in the end.
>
> Can we put this function into, say, mm/pgtable-generic.c?
> Finding all the places that do such walk and sticking it there should not
> be a part of this set IMNHO, but having it in the generic code is a good
> start for a future cleanup.

Yeah, this is the kinda subtlety I always run into when trying to play
with pagetable code, and I end up being timid. The thing is that
mm_find_pmd() bails when it finds a non-present entry.

I think in this case it's fine, so yeah we could at least move
mm_find_pmd(), change the mm arg to a pgd_t*, rename it, and call it
from here.

>> +{
>> +	p4d_t *p4d;
>> +	pud_t *pud;
>> +
>> +	if (pgd->pgd == 0)
>> +		return NULL;
>> +
>> +	p4d = p4d_offset(pgd, va);
>> +	if (p4d_none(*p4d))
>> +		return NULL;
>> +
>> +	pud = pud_offset(p4d, va);
>> +	if (pud_none(*pud))
>> +		return NULL;
>> +
>> +	return pmd_offset(pud, va);
>> +}