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

[David Hildenbrand]

On 10.06.25 15:24, David Hildenbrand wrote:
> 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.

Note that I am also not quite happy bout that function name, but I think 
we should add a proper interface that documents clearly when it is even 
okay to call that function ...

--
Cheers,

David / dhildenb