Re: [PATCH v3 08/22] mm: Allow page table accessors to be non-idempotent

[David Hildenbrand (Red Hat)]

On 11/27/25 17:57, Ryan Roberts wrote:
> On 13/11/2025 01:45, Samuel Holland wrote:
> > Currently, some functions such as pte_offset_map() are passed both
> > pointers to hardware page tables, and pointers to previously-read PMD
> > entries on the stack. To ensure correctness in the first case, these
> > functions must use the page table accessor function (pmdp_get()) to
> > dereference the supplied pointer. However, this means pmdp_get() is
> > called twice in the second case. This double call must be avoided if
> > pmdp_get() applies some non-idempotent transformation to the value.
> >
> > Avoid the double transformation by calling set_pmd() on the stack
> > variables where necessary to keep set_pmd()/pmdp_get() calls balanced.
>
> I don't think this is a good solution.

Agreed,

	set_pmd(&pmd, pmd);

is rather horrible.

--
Cheers

David