Re: [PATCH 3/6] mm/vma: only permit MAP_PRIVATE /dev/zero to be mapped anonymous

[Lorenzo Stoakes (ARM)]

On Mon, Sep 07, 2026 at 09:54:04PM +0200, David Hildenbrand (Arm) wrote:
> Yes, but my point is that the comment
>
> "cannot mark themselves anonymous"
>
> will not really be correct after the next patch, no?

Ah ok ack I get your point. I will update this comment in the next patch.

> >>>  		set_vma_user_defined_fields(vma, &map);
> >>
> >> Ah, we have mmap_zero_prepare() for handling the shmem_zero_setup_desc(). I was
> >> just about to ask whether we can just get rid of this here.
> >>
> >>
> >> But, hold on, do we now even need that? Could core-mm now take care of that as
> >> well, and we could just remove mmap_zero_prepare() entirely?
> >>
> >> That is, we'd make shmem_zero_setup() in __mmap_new_vma() take care of this?
> >> Then we might not even need shmem_zero_setup_desc() anymore.
> >>
> >> Maybe harder than it sounds at first.
> >
> > I think I'd rather that be a follow up :) this series is about eliminiating the
> > one last (I hope?) corner case for anon VMAs.
> Right; having to deal with anonymous mappings that have mmap_prepare is rather
> suboptimal. Ideally we'd just handle the odd dev-zero special-casing early in
> the mmap path also for MAP_SHARED, and avoid messing with mmap_prepare entirely.
>
> So agreed that this can be done separately.

Yeah, really life will be easier once the mmap path is gone in general :)

>
> --
> Cheers,
>
> David

--
Cheers, Lorenzo