add remap_pfn_range_notrack instead of reinventing it in i915

[Daniel Vetter]

On Mon, Mar 01, 2021 at 09:33:18AM +0100, Christoph Hellwig wrote:
> Hi all,
> 
> i915 has some reason to want to avoid the track_pfn_remap overhead in
> remap_pfn_range.  Add a function to the core VM to do just that rather
> than reinventing the functionality poorly in the driver.

It's not _notrack it's "rely on the tracking established by the struct
io_mapping". Exporting a _notrack version to drivers sounds like not
something we want to ever do. So I think you want a helper which takes the
io_mapping, and not something that encourages drivers to go full stupid.

> Note that the remap_io_sg path does get exercises when using Xorg on my
> Thinkpad X1, so this should be considered lightly tested, I've not
> managed to hit the remap_io_mapping path at all.

Needs an older machine and old userspace. intel-gfx CI should still check
whether it's all ok.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch