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

On Mon, Oct 12, 2026 at 05:08:09PM +0200, David Hildenbrand (Arm) wrote:

On 10/9/26 20:04, Lorenzo Stoakes (ARM) wrote:

quoted

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@kernel.org>

Thanks!

--
Cheers, Lorenzo