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

[David Hildenbrand <david@redhat.com>]

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