Re: [Intel-gfx] [PATCH 2/4] mm: add a io_mapping_map_user helper

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Oct 20, 2021 at 08:40:05AM -0700, Lucas De Marchi wrote:
> On Fri, Mar 26, 2021 at 06:55:03AM +0100, Christoph Hellwig wrote:
> > Add a helper that calls remap_pfn_range for an struct io_mapping, relying
> > on the pgprot pre-validation done when creating the mapping instead of
> > doing it at runtime.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> > include/linux/io-mapping.h |  3 +++
> > mm/Kconfig                 |  3 +++
> > mm/Makefile                |  1 +
> > mm/io-mapping.c            | 29 +++++++++++++++++++++++++++++
> > 4 files changed, 36 insertions(+)
> > create mode 100644 mm/io-mapping.c
> > 
> > diff --git a/include/linux/io-mapping.h b/include/linux/io-mapping.h
> > index c093e81310a9b3..e9743cfd858527 100644
> > --- a/include/linux/io-mapping.h
> > +++ b/include/linux/io-mapping.h
> > @@ -220,3 +220,6 @@ io_mapping_free(struct io_mapping *iomap)
> > }
> > 
> > #endif /* _LINUX_IO_MAPPING_H */
> > +
> > +int io_mapping_map_user(struct io_mapping *iomap, struct vm_area_struct *vma,
> > +		unsigned long addr, unsigned long pfn, unsigned long size);
> 
> I'm not sure what exactly brought me to check this, but while debugging
> I noticed this outside the header guard. But then after some more checks I
> saw nothing actually selects CONFIG_IO_MAPPING because commit using
> it was reverted in commit 0e4fe0c9f2f9 ("Revert "i915: use io_mapping_map_user"")
> 
> Is this something we want to re-attempt moving to mm/ ?

Yes, it would be very good to unexport apply_to_page_range(), it's a
terrible interface to expose.