Re: [PATCH 3/3] mm/devmap: Remove pgmap accounting in the get_user_pages_fast() path

[Jason Gunthorpe]

On Mon, Mar 29, 2021 at 04:24:19PM -0700, Dan Williams wrote:
> On Thu, Mar 25, 2021 at 7:34 AM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> >
> > On Thu, Mar 18, 2021 at 10:03:06AM -0700, Dan Williams wrote:
> > > Yes. I still need to answer the question of whether mapping
> > > invalidation triggers longterm pin holders to relinquish their hold,
> > > but that's a problem regardless of whether gup-fast is supported or
> > > not.
> >
> > It does not, GUP users do not interact with addres_space or mmu
> > notifiers
> 
> Ok, but the SIGKILL from the memory_failure() will drop the pin?

In the general case I doubt it..

I think this is fine, we shouldn't expect unplugging a driver to not
block if there are open users.

Demading DMA users to be able to shoot down access to system memory is
a really big kernel change.

Jason