Re: [PATCH v2 14/19] mm: Add vdso_base in mm_struct

[Andy Lutomirski]

On Mon, Nov 23, 2020 at 4:29 PM Dmitry Safonov <dima@xxxxxxxxxx> wrote:
>
> Instead of having every architecture to define vdso_base/vdso_addr etc,
> provide a generic mechanism to track vdso_base for landing in userspace.
> It'll minimize per-architecture difference, the number of callbacks to
> provide.
>
> Originally, it started from thread [1] where the need for .close()
> callback on vm_special_mapping was pointed, this generic code besides
> removing duplicated .mremap() callbacks provides a cheaper way to
> support munmap() on vdso mappings without introducing .close() callbacks
> for every architecture (with would bring even more code duplication).

I admit I'm slightly dubious about passing in the old vma and
comparing its start address as opposed to using some more explicit "is
this the vdso" check, but I guess I'm okay with that.