Re: [PATCH 2/2] mm: soft_dirty: userfaultfd: introduce wrprotect_tlb_flush_pending

[Linus Torvalds]

On Thu, Jan 7, 2021 at 2:14 PM John Hubbard <jhubbard@xxxxxxxxxx> wrote:
> >
> > Literally just adding a " && page_mapcount(page) == 1" in there
> > (probably best done inside page_maybe_dma_pinned() itself)
>
> Well, that means that pages that are used for pinned DMA like this, can
> not be shared with other processes. Is that an acceptable limitation
> for the RDMA users? It seems a bit constraining, at first glance anyway.

Hmm, add a check for the page being PageAnon(), perhaps?

If it's a shared vma, then the page can be pinned shared with multiple
mappings, I agree.

So yeah, I didn't think it through entirely.. And maybe I'm still
missing something else..

          Linus