Re: [PATCH v7 5/8] mm: Device exclusive memory access

From: Jason Gunthorpe
Date: Wed Mar 31 2021 - 09:46:55 EST


On Thu, Apr 01, 2021 at 12:27:52AM +1100, Alistair Popple wrote:
> On Thursday, 1 April 2021 12:18:54 AM AEDT Jason Gunthorpe wrote:
> > On Wed, Mar 31, 2021 at 11:59:28PM +1100, Alistair Popple wrote:
> >
> > > I guess that makes sense as the split could go either way at the
> > > moment but I should add a check to make sure this isn't used with
> > > pinned pages anyway.
> >
> > Is it possible to have a pinned page under one of these things? If I
> > pin it before you migrate it then it remains pinned but hidden under
> > the swap entry?
>
> At the moment yes. But I had planned (and this reminded me) to add a check to
> prevent marking pinned pages for exclusive access.

How do you even do that without races with GUP fast?

Jason