Re: [PATCH v5 1/7] mm, devm_memremap_pages: Mark devm_memremap_pages() EXPORT_SYMBOL_GPL

[Logan Gunthorpe]

On 12/09/18 08:22 PM, Dan Williams wrote:
> devm_memremap_pages() is a facility that can create struct page entries
> for any arbitrary range and give drivers the ability to subvert core
> aspects of page management.
> 
> Specifically the facility is tightly integrated with the kernel's memory
> hotplug functionality. It injects an altmap argument deep into the
> architecture specific vmemmap implementation to allow allocating from
> specific reserved pages, and it has Linux specific assumptions about
> page structure reference counting relative to get_user_pages() and
> get_user_pages_fast(). It was an oversight and a mistake that this was
> not marked EXPORT_SYMBOL_GPL from the outset.
> 
> Again, devm_memremap_pagex() exposes and relies upon core kernel
> internal assumptions and will continue to evolve along with 'struct
> page', memory hotplug, and support for new memory types / topologies.
> Only an in-kernel GPL-only driver is expected to keep up with this
> ongoing evolution. This interface, and functionality derived from this
> interface, is not suitable for kernel-external drivers.
> 
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: "JÃrÃme Glisse" <jglisse@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Reviewed-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>

Mostly to say that I agree with you and Christoph on this debate and
that the change to GPL does not affect my P2PDMA work.

Logan