Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM

[Tomasz Figa]

On Wed, Oct 7, 2020 at 2:44 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
>
> On Wed, Oct 07, 2020 at 02:33:56PM +0200, Marek Szyprowski wrote:
> > Well, it was in vb2_get_vma() function, but now I see that it has been
> > lost in fb639eb39154 and 6690c8c78c74 some time ago...
>
> There is no guarentee that holding a get on the file says anthing
> about the VMA. This needed to check that the file was some special
> kind of file that promised the VMA layout and file lifetime are
> connected.
>
> Also, cloning a VMA outside the mm world is just really bad. That
> would screw up many assumptions the drivers make.
>
> If it is all obsolete I say we hide it behind a default n config
> symbol and taint the kernel if anything uses it.
>
> Add a big comment above the follow_pfn to warn others away from this
> code.

Sadly it's just verbally declared as deprecated and not formally noted
anyway. There are a lot of userspace applications relying on user
pointer support.