Rewrite copy_huge_page() and move it into mm/util.c so it's always
available. Fixes an exposure of uninitialised memory on configurations
with HUGETLB and UFFD enabled and MIGRATION disabled.
Fixes: 8cc5fcbb5be8 ("mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY") Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>