linux-kernel - Re: [PATCH v3 7/8] mm, hmm: Mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL

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Date:   Fri, 6 Jul 2018 16:53:11 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Christoph Hellwig <hch@....de>, Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 7/8] mm, hmm: Mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL_GPL

On Mon, Jun 18, 2018 at 11:05 PM, Dan Williams <dan.j.williams@...el.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@...hat.com>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Dan Williams <dan.j.williams@...el.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).