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

[Alistair Popple]

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
>