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

Message ID 153680532635.453305.11297363695024516117.stgit@dwillia2-desk3.amr.corp.intel.com (mailing list archive)
State New, archived
Headers show
Series mm: Merge hmm into devm_memremap_pages, mark GPL-only | expand

Commit Message

Dan Williams Sept. 13, 2018, 2:22 a.m. UTC 
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@suse.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 kernel/memremap.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Logan Gunthorpe Sept. 13, 2018, 4:25 p.m. UTC | #1 
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@suse.com>
> Cc: "Jérôme Glisse" <jglisse@redhat.com>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Reviewed-by: Logan Gunthorpe <logang@deltatee.com>

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
diff mbox series

Patch

diff --git a/kernel/memremap.c b/kernel/memremap.c
index 5b8600d39931..f95c7833db6d 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -283,7 +283,7 @@  void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
 	pgmap_radix_release(res, pgoff);
 	return ERR_PTR(error);
 }
-EXPORT_SYMBOL(devm_memremap_pages);
+EXPORT_SYMBOL_GPL(devm_memremap_pages);
 
 unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
 {