Re: [PATCH v3 7/8] mm, hmm: Mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL_GPL

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 6 Jul 2018 16:53:11 -0700 Dan Williams <dan.j.williams@intel.com> wrote:

> On Mon, Jun 18, 2018 at 11:05 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > The routines hmm_devmem_add(), and hmm_devmem_add_resource() are
> > now wrappers around the functionality provided by devm_memremap_pages() to
> > inject a dev_pagemap instance and hook page-idle events. The
> > devm_memremap_pages() interface is base infrastructure for HMM which has
> > more and deeper ties into the kernel memory management implementation
> > than base ZONE_DEVICE.
> >
> > Originally, the HMM page structure creation routines copied the
> > devm_memremap_pages() code and reused ZONE_DEVICE. A cleanup to unify
> > the implementations was discussed during the initial review:
> > http://lkml.iu.edu/hypermail/linux/kernel/1701.2/00812.html
> >
> > Given that devm_memremap_pages() is marked EXPORT_SYMBOL_GPL by its
> > authors and the hmm_devmem_{add,add_resource} routines are simple
> > wrappers around that base, mark these routines as EXPORT_SYMBOL_GPL as
> > well.
> >
> > Cc: "Jérôme Glisse" <jglisse@redhat.com>
> > Cc: Logan Gunthorpe <logang@deltatee.com>
> > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> 
> Currently OpenAFS is blocked from compiling with the 4.18 series due
> to the current state of put_page() inadvertently pulling in GPL-only
> symbols. This series, "PATCH v3 0/8] mm: Rework hmm to use
> devm_memremap_pages and other fixes" corrects that situation and
> corrects HMM's usage of EXPORT_SYMBOL_GPL.
> 
> If HMM wants to export functionality to out-of-tree proprietary
> drivers it should do so without consuming GPL-only exports, or
> consuming internal-only public functions in its exports.
> 
> In addition to duplicating devm_memremap_pages(), that should have
> been EXPORT_SYMBOL_GPL from the beginning, it is also exporting /
> consuming these GPL-only symbols via HMM's EXPORT_SYMBOL entry points.
> 
>     mmu_notifier_unregister_no_release
>     percpu_ref
>     region_intersects
>     __class_create
> 
> Those entry points also consume / export functionality that is
> currently not exported to any other driver.
> 
>     alloc_pages_vma
>     walk_page_range
> 
> Andrew, please consider applying this v3 series to fix this up (let me
> know if you need a resend).

A resend would be good.  And include the above info in the changelog.

I can't say I'm terribly happy with the HMM situation.  I was under the
impression that a significant number of significant in-tree drivers
would be using HMM but I've heard nothing since, apart from ongoing
nouveau work, which will be perfectly happy with GPL-only exports.

So yes, we should revisit the licensing situation and, if only nouveau
will be using HMM we should revisit HMM's overall usefulness.