On Wed, Jan 13, 2021 at 04:43:37PM -0800, Dan Williams wrote:

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 looked up by get_user_pages().
I.e. metadata pfns are never user mapped.

Fixes: 6100e34b2526 ("mm, memory_failure: Teach memory_failure() about dev_pagemap pages")
Cc: Naoya Horiguchi <redacted>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: David Hildenbrand <redacted>
Reviewed-by: David Hildenbrand <redacted>
Signed-off-by: Dan Williams <redacted>

Looks fine to me.

Reviewed-by: Naoya Horiguchi <redacted>