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Date:   Sun, 30 Apr 2023 00:09:35 +0100
From:   Lorenzo Stoakes <lstoakes@gmail.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
Cc:     Theodore Ts'o <tytso@mit.edu>,
        David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
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Subject: Re: [PATCH v5] mm/gup: disallow GUP writing to file-backed mappings
 by default
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On Sat, Apr 29, 2023 at 08:01:11PM -0300, Jason Gunthorpe wrote:
> On Sat, Apr 29, 2023 at 12:21:09AM -0400, Theodore Ts'o wrote:
>
> > In any case, the file system maintainers' position (mine and I doubt
> > Dave Chinner's position has changed) is that if you write to
> > file-backed mappings via GUP/RDMA/process_vm_writev, and it causes
> > silent data corruption, you get to keep both pieces, and don't go
> > looking for us for anything other than sympathy...
>
> This alone is enough reason to block it. I'm tired of this round and
> round and I think we should just say enough, the mm will work to
> enforce this view point. Files can only be written through PTEs.
>
> If this upsets people they can work on fixing it, but at least we
> don't have these kernel problems and inconsistencies to deal with.
>

Indeed, I think there is a broad consensus that FOLL_LONGTERM is such an
egregious case that this is the way forward.

I will respin with the discussed GUP-fast changes relatively soon and then
we can see where that takes us :)

> Jason