nvdimm/region: Fix default alignment for small regions

[ Upstream commit d9d290d ]

In preparation for removing BLK aperture support the NVDIMM unit tests
discovered that the default alignment can be set higher than the
capacity of the region. Fall back to PAGE_SIZE in that case.

Given this has not been seen in the wild, elide notifying -stable.

Fixes: 2522afb ("libnvdimm/region: Introduce an 'align' attribute")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/164688416128.2879318.17890707310125575258.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/nvdimm/region_devs.c

@@ -1025,6 +1025,9 @@ static unsigned long default_align(struct nd_region *nd_region)
 		}
 	}
 
+	if (nd_region->ndr_size < MEMREMAP_COMPAT_ALIGN_MAX)
+		align = PAGE_SIZE;
+
 	mappings = max_t(u16, 1, nd_region->ndr_mappings);
 	div_u64_rem(align, mappings, &remainder);
 	if (remainder)