On Sat, Jan 16, 2021 at 3:05 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I'll go think about this.
>
> Martin, since you can apparently trigger the problem easily, hopefully
> you're willing to try a couple of patches?

Hmm. It might end up being as simple as the attached patch.

I'm not super-happy with this situation (that whole nasty security
issue had some horrible cascading problems), and this only really
fixes _pinned_ pages.

In particular, somebody doing a plain get_user_pages() for writing can
still hit issues (admittedly that's true in general, but the vm
changes made it much more obviously true).

But for the case of io_uring buffers, this looks like the obvious simple fix.

I don't have a load to test this with, so I'll come back to ask Martin
to do so...

                 Linus