Re: [PATCH v5 08/15] mm: Add unsafe_follow_pfn

Daniel Vetter
2020-11-02T12:56:29Z

On Mon, Nov 2, 2020 at 8:29 AM Christoph Hellwig <hch@infradead.org> wrote:
>
> On Fri, Oct 30, 2020 at 11:08:08AM +0100, Daniel Vetter wrote:
> > Also mark up follow_pfn as EXPORT_SYMBOL_GPL. The only safe way to use
> > that by drivers/modules is together with an mmu_notifier, and that's
> > all _GPL stuff.
>
> I also think it also needs to be renamed to explicitly break any existing
> users out of tree or int the submission queue.

Ok I looked at the mmu notifier locking again and noticed that
mm->subscriptions has its own spinlock. Since there usually shouldn't
be a huge pile of these I think it's feasible to check for the mmu
notifier in follow_pfn. And that would stuff this gap for good. I'll
throw that on top as a final patch and see what people think.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation