873aefb376
There's currently a reference count leak on the zero page. We increment the reference via pin_user_pages_remote(), but the page is later handled as an invalid/reserved page, therefore it's not accounted against the user and not unpinned by our put_pfn(). Introducing special zero page handling in put_pfn() would resolve the leak, but without accounting of the zero page, a single user could still create enough mappings to generate a reference count overflow. The zero page is always resident, so for our purposes there's no reason to keep it pinned. Therefore, add a loop to walk pages returned from pin_user_pages_remote() and unpin any zero pages. Cc: stable@vger.kernel.org Reported-by: Luboslav Pivarc <lpivarc@redhat.com> Reviewed-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/166182871735.3518559.8884121293045337358.stgit@omen Signed-off-by: Alex Williamson <alex.williamson@redhat.com>