Currently memremap checks if the range is "System RAM" and returns the
kernel linear address.  This is broken for highmem platforms where a
range may be "System RAM", but is not part of the kernel linear mapping.
Fallback to ioremap_cache() in these cases, to let the arch code attempt
to handle it.

Note that ARM ioremap will WARN when attempting to remap ram, and in
that case the caller needs to be fixed.  For this reason, existing
ioremap_cache() usages for ARM are already trained to avoid attempts to
remap ram.

The impact of this bug is low for now since the pmem driver is the only
user of memremap(), but this is important to fix before more conversions
to memremap arrive in 4.4.

Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reported-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Given that pmem ranges come with numa-locality hints, arrange for the
resulting driver objects to be obtained from node-local memory.
Reviewed-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Hint to closest numa node for the placement of newly allocated pages.
As that is where the device's other allocations will originate by
default when it does not specify a NUMA node.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Make devm_memremap consistent with the error return scheme of
devm_memremap_pages to remove special casing in the pmem driver.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Remove open coded call to memunmap.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

This behaves like devm_memremap except that it ensures we have page
structures available that can back the region.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
[djbw: catch attempts to remap RAM, drop flags]
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

Existing users of ioremap_cache() are mapping memory that is known in
advance to not have i/o side effects.  These users are forced to cast
away the __iomem annotation, or otherwise neglect to fix the sparse
errors thrown when dereferencing pointers to this memory.  Provide
memremap() as a non __iomem annotated ioremap_*() in the case when
ioremap is otherwise a pointer to cacheable memory. Empirically,
ioremap_<cacheable-type>() call sites are seeking memory-like semantics
(e.g.  speculative reads, and prefetching permitted).

memremap() is a break from the ioremap implementation pattern of adding
a new memremap_<type>() for each mapping type and having silent
compatibility fall backs.  Instead, the implementation defines flags
that are passed to the central memremap() and if a mapping type is not
supported by an arch memremap returns NULL.

We introduce a memremap prototype as a trivial wrapper of
ioremap_cache() and ioremap_wt().  Later, once all ioremap_cache() and
ioremap_wt() usage has been removed from drivers we teach archs to
implement arch_memremap() with the ability to strictly enforce the
mapping type.

Cc: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>