Re: [PATCH v5 13/38] bpf: arena: mark arena_map_mmap() mappings VM_MIXEDMAP

[Lorenzo Stoakes (ARM)]

On Mon, Oct 12, 2026 at 05:08:09PM +0200, David Hildenbrand (Arm) wrote:
> On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote:

> > diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c
> > index 7b6847200b43..b69fe5e34339 100644
> > --- a/kernel/bpf/arena.c
> > +++ b/kernel/bpf/arena.c
> > @@ -620,8 +620,9 @@ static int arena_map_mmap(struct bpf_map *map, struct vm_area_struct *vma)
> >  	 * clears VM_MAYEXEC. Set VM_DONTEXPAND to avoid potential change
> >  	 * of user_vm_start. Set VM_DONTCOPY to prevent arena VMA from
> >  	 * being copied into the child process on fork.
> > +	 * This is a kernel page so set VM_MIXEDMAP.
> >  	 */
> > -	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTCOPY);
> > +	vm_flags_set(vma, VM_MIXEDMAP | VM_DONTEXPAND | VM_DONTCOPY);
> >  	vma->vm_ops = &arena_vm_ops;
> >  	return 0;
> >  }
> >
>
> Historically, VM_MIXEDMAP really just means: can contain refcounted and
> non-refcounted things. Everything with a struct page is refcounted.
>
> I think we are now changing the semantics to mean "maps kernel pages". I think

Yes.

It was sort of implicit before given insert_page() etc. but still really meaning
that it _might_ be both.

> this is fine, but we really have to update the documentation (and possibly
> rename this thing to something more expressive?)

Yeah I completely agree.

I will rename it, but I think that's best for 7.5 obviously! :)

>
> Acked-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>

Thanks!

--
Cheers, Lorenzo