On Tue 20-11-18 15:12:54, 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.
As I've said earlier I do not buy this justification because there is
simply no stable API for modules by definition
(Documentation/process/stable-api-nonsense.rst). I do understand
your reasoning that you as an author never intended to export the symbol
this way. That is fair and justified reason for this patch.
Whoever needs a wrapper around arch_add_memory can do so because this
symbol has no restriction for the usage. It will be still the same
fiddling with struct page and deep mm internals. Do we care? I am not
convinced because once we grow any in tree user we have to cope with any
potential abuse like we have in other areas in the past. And out-of-tree
modules? Who cares. Those are on their own completely and have their
ways to go around.
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
That being said
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> kernel/memremap.c | 2 +-
> tools/testing/nvdimm/test/iomap.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index 9eced2cc9f94..61dbcaa95530 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -233,7 +233,7 @@ void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> err_array:
> return ERR_PTR(error);
> }
> -EXPORT_SYMBOL(devm_memremap_pages);
> +EXPORT_SYMBOL_GPL(devm_memremap_pages);
>
> unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
> {
> diff --git a/tools/testing/nvdimm/test/iomap.c b/tools/testing/nvdimm/test/iomap.c
> index ff9d3a5825e1..ed18a0cbc0c8 100644
> --- a/tools/testing/nvdimm/test/iomap.c
> +++ b/tools/testing/nvdimm/test/iomap.c
> @@ -113,7 +113,7 @@ void *__wrap_devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap)
> return nfit_res->buf + offset - nfit_res->res.start;
> return devm_memremap_pages(dev, pgmap);
> }
> -EXPORT_SYMBOL(__wrap_devm_memremap_pages);
> +EXPORT_SYMBOL_GPL(__wrap_devm_memremap_pages);
>
> pfn_t __wrap_phys_to_pfn_t(phys_addr_t addr, unsigned long flags)
> {
--
Michal Hocko
SUSE Labs
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