On Tue, Apr 16, 2019 at 9:16 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> We actually already *have* this function.
>
> It's called "gup_fast_permitted()" and it's used by x86-64 to verify
> the proper address range. Exactly like s390 needs..
>
> Could you please use that instead?

IOW, something like the attached.

Obviously untested. And maybe 'current' isn't declared in
<asm/pgtable.h>, in which case you'd need to modify it to instead make
the inline function be "s390_gup_fast_permitted()" that takes a
pointer to the mm, and do something like

  #define gup_fast_permitted(start, pages) \
         s390_gup_fast_permitted(current->mm, start, pages)

instead.

But I think you get the idea..

                Linus