Re: [PATCH v2 1/2] mm: Allow lockless kernel pagetable walking

[David Hildenbrand]

On 10.06.25 14:07, Lorenzo Stoakes wrote:
> OK so I think the best solution here is to just update check_ops_valid(), which
> was kind of sucky anyway (we check everywhere but walk_page_range_mm() to
> enforce the install pte thing).
>
> Let's do something like:
>
> #define OPS_MAY_INSTALL_PTE	(1<<0)
> #define OPS_MAY_AVOID_LOCK	(1<<1)
>
> and update check_ops_valid() to take a flags or maybe 'capabilities' field.
>
> Then check based on this e.g.:
>
> if (ops->install_pte && !(capabilities & OPS_MAY_INSTALL_PTE))
> 	return false;
>
> if (ops->walk_lock == PGWALK_NOLOCK && !(capabilities & OPS_MAY_AVOID_LOCK))
> 	return false;

Hm. I mean, we really only want to allow this lockless check for 
walk_kernel_page_table_range(), right?

Having a walk_kernel_page_table_range_lockeless() might (or might not) 
be better, to really only special-case this specific path.

So, I am wondering if we should further start splitting the 
kernel-page-table walker up from the mm walker, at least on the "entry" 
function for now.

--
Cheers,

David / dhildenb