Nouveau - Mar 2021 - [PATCH v7 5/8] mm: Device exclusive memory access

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?

So the special logic is needed and the pinned page has to be copied
and written as a normal pte, not dropped as a migration entry

Jason

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. This check was in the 
original migration based implementation as I don't think it makes much sense
to allow exclusive access to pinned pages given it indicates another device is 
possibly using it. 
> So the special logic is needed and the pinned page has to be copied
> and written as a normal pte, not dropped as a migration entry
Yep, if we end up allowing pinned pages to exist under these then that makes 
sense. Thanks for the clarification.

 - Alistair
> Jason
>