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

[Andy Lutomirski]

On Sat, Nov 7, 2020 at 9:18 PM Dmitry Safonov <dima@xxxxxxxxxx> wrote:
>
> Instead of having every architecture to define vdso_base/vdso_addr etc,
> provide a generic mechanism to track 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 find the naming odd.  It's called "user_landing", which is
presumably a hard-to-understand shorthand for "user mode landing pad
for return from a signal handler if SA_RESTORER is not set".  But,
looking at the actual code, it's not this at all -- it's just the vDSO
base address.

So how about just calling it vdso_base?  I'm very much in favor of
consolidating and cleaning up, and improving the vdso remap/unmap
code, but I'm not convinced that we should call it anything other than
the vdso base.

--Andy