[PATCH 2/2] mm: fix mixed zone detection in devm_memremap_pages

[Dan Williams <dan.j.williams@intel.com>]

The check for whether we overlap "System RAM" needs to be done at
section granularity.  For example a system with the following mapping:

    100000000-37bffffff : System RAM
    37c000000-837ffffff : Persistent Memory

...is unable to use devm_memremap_pages() as it would result in two
zones colliding within a given section.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 kernel/memremap.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/memremap.c b/kernel/memremap.c
index b981a7b023f0..4c7d08339f62 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -270,9 +270,10 @@ struct dev_pagemap *find_dev_pagemap(resource_size_t phys)
 void *devm_memremap_pages(struct device *dev, struct resource *res,
 		struct percpu_ref *ref, struct vmem_altmap *altmap)
 {
-	int is_ram = region_intersects(res->start, resource_size(res),
-			"System RAM");
-	resource_size_t key, align_start, align_size, align_end;
+	resource_size_t align_start = res->start & ~(SECTION_SIZE - 1);
+	resource_size_t align_size = ALIGN(resource_size(res), SECTION_SIZE);
+	int is_ram = region_intersects(align_start, align_size, "System RAM");
+	resource_size_t key, align_end;
 	struct dev_pagemap *pgmap;
 	struct page_map *page_map;
 	unsigned long pfn;
@@ -314,8 +315,6 @@ void *devm_memremap_pages(struct device *dev, struct resource *res,
 
 	mutex_lock(&pgmap_lock);
 	error = 0;
-	align_start = res->start & ~(SECTION_SIZE - 1);
-	align_size = ALIGN(resource_size(res), SECTION_SIZE);
 	align_end = align_start + align_size - 1;
 	for (key = align_start; key <= align_end; key += SECTION_SIZE) {
 		struct dev_pagemap *dup;

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