[PATCH v3 5/6] mm: Fix memory_failure() handling of dax-namespace metadata

[Dan Williams]

Given 'struct dev_pagemap' spans both data pages and metadata pages be
careful to consult the altmap if present to delineate metadata. In fact
the pfn_first() helper already identifies the first valid data pfn, so
export that helper for other code paths via pgmap_pfn_valid().

Other usage of get_dev_pagemap() are not a concern because those are
operating on known data pfns having been looking up by get_user_pages().
I.e. metadata pfns are never user mapped.

Cc: Naoya Horiguchi <naoya.horigu...@nec.com>
Cc: Andrew Morton <a...@linux-foundation.org>
Reported-by: David Hildenbrand <da...@redhat.com>
Signed-off-by: Dan Williams <dan.j.willi...@intel.com>
---
 include/linux/memremap.h |    6 ++++++
 mm/memory-failure.c      |    6 ++++++
 mm/memremap.c            |   15 +++++++++++++++
 3 files changed, 27 insertions(+)

diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index 79c49e7f5c30..f5b464daeeca 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -137,6 +137,7 @@ void *devm_memremap_pages(struct device *dev, struct 
dev_pagemap *pgmap);
 void devm_memunmap_pages(struct device *dev, struct dev_pagemap *pgmap);
 struct dev_pagemap *get_dev_pagemap(unsigned long pfn,
                struct dev_pagemap *pgmap);
+bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn);
 
 unsigned long vmem_altmap_offset(struct vmem_altmap *altmap);
 void vmem_altmap_free(struct vmem_altmap *altmap, unsigned long nr_pfns);
@@ -165,6 +166,11 @@ static inline struct dev_pagemap *get_dev_pagemap(unsigned 
long pfn,
        return NULL;
 }
 
+static inline bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long 
pfn)
+{
+       return false;
+}
+
 static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
 {
        return 0;
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 78b173c7190c..541569cb4a99 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -1308,6 +1308,12 @@ static int memory_failure_dev_pagemap(unsigned long pfn, 
int flags,
                 */
                put_page(page);
 
+       /* device metadata space is not recoverable */
+       if (!pgmap_pfn_valid(pgmap, pfn)) {
+               rc = -ENXIO;
+               goto out;
+       }
+
        /*
         * Prevent the inode from being freed while we are interrogating
         * the address_space, typically this would be handled by
diff --git a/mm/memremap.c b/mm/memremap.c
index 16b2fb482da1..2455bac89506 100644
--- a/mm/memremap.c
+++ b/mm/memremap.c
@@ -80,6 +80,21 @@ static unsigned long pfn_first(struct dev_pagemap *pgmap, 
int range_id)
        return pfn + vmem_altmap_offset(pgmap_altmap(pgmap));
 }
 
+bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn)
+{
+       int i;
+
+       for (i = 0; i < pgmap->nr_range; i++) {
+               struct range *range = &pgmap->ranges[i];
+
+               if (pfn >= PHYS_PFN(range->start) &&
+                   pfn <= PHYS_PFN(range->end))
+                       return pfn >= pfn_first(pgmap, i);
+       }
+
+       return false;
+}
+
 static unsigned long pfn_end(struct dev_pagemap *pgmap, int range_id)
 {
        const struct range *range = &pgmap->ranges[range_id];