Subject: Re: [PATCH v6 3/3] mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings

From: Jason Gunthorpe <[email-masked]>
Date: Tue, 2 May 2023 10:50:58 -0300

On Tue, May 02, 2023 at 03:47:43PM +0200, David Hildenbrand wrote:
> > Eventually we want to implement a mechanism where we can dynamically pin in response to RPCIT.
> 
> Okay, so IIRC we'll fail starting the domain early, that's good. And if we
> pin all guest memory (instead of small pieces dynamically), there is little
> existing use for file-backed RAM in such zPCI configurations (because memory
> cannot be reclaimed either way if it's all pinned), so likely there are no
> real existing users.

Right, this is VFIO, the physical HW can't tolerate not having pinned
memory, so something somewhere is always pinning it.

Which, again, makes it weird/wrong that this KVM code is pinning it
again :\

Jason