Re: [SECURITY] mm: khugepaged collapse_file() drops RWP PTE markers

["David Hildenbrand (Arm)" <david@kernel.org>]

On 11/11/26 21:55, Linus Torvalds wrote:
> On Wed, 11 Nov 2026 at 12:20, David Hildenbrand (Arm) <david@kernel.org> wrote:
>>
>> It would be a lot more consistent if we'd just add marker support. Or is there a
>> good reason why that is explicitly not wanted?
> 
> Let's not help people do things that won't work on older kernels for
> no real gain.

Uffd folks usually indicate such things through new uffd features.

> 
> Is there an actual real-life user that would care and be enormously
> helped by such a thing and it would increase performance or something?
> That sounds very unlikely, since presumably re-faulting never happens
> in practice, so just tracking it in user space is "free".
> 
> In the absence of some real load with a real argument for it, please
> let's just document existing behavior to the fact that you need to
> simply see the re-faulting of these things..
Just to express why I would even dare proposing to implement something in
userfaultfd: in Kiryl's series we abstracted the uffd-wp PTE bit to a uffd PTE
bit, which made things more generic.

Abstracting uffd-wp markers to uffd markers would similarly make things more
generic.

A quick codex prompt tells me: 90 insertions, 95 deletions.

But most changes are documentation either way, so that doesn't reflect reality.

Now let's ignore what I wrote above, I just polished another uffd fix and most
fixes I looked at throughout the last days were uffd related, which is starting
to get annoying.

So yes, no new uffd features.

-- 
Cheers,

David