Re: [PATCH 1/5] mm: Introduce mm_struct.has_pinned

Peter Xu
2020-09-21T22:30:12Z

On Mon, Sep 21, 2020 at 11:43:38PM +0200, Jann Horn wrote:
> On Mon, Sep 21, 2020 at 11:17 PM Peter Xu <peterx@redhat.com> wrote:
> >
> > (Commit message collected from Jason Gunthorpe)
> >
> > Reduce the chance of false positive from page_maybe_dma_pinned() by keeping
> > track if the mm_struct has ever been used with pin_user_pages(). mm_structs
> > that have never been passed to pin_user_pages() cannot have a positive
> > page_maybe_dma_pinned() by definition.
>
> There are some caveats here, right? E.g. this isn't necessarily true
> for pagecache pages, I think?

Sorry I didn't follow here. Could you help explain with some details?

Thanks,

--
Peter Xu