CVE-2021-47214

In the Linux kernel, the following vulnerability has been resolved:
hugetlb, userfaultfd: fix reservation restore on userfaultfd error
Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we bail
out using “goto out_release_unlock;” in the cases where idx >= size, or
!huge_pte_none(), the code will detect that new_pagecache_page == false,
and so call restore_reserve_on_error(). In this case I see
restore_reserve_on_error() delete the reservation, and the following call
to remove_inode_hugepages() will increment h->resv_hugepages causing a 100%
reproducible leak. We should treat the is_continue case similar to adding a
page into the pagecache and set new_pagecache_page to true, to indicate
that there is no reservation to restore on the error path, and we need not
call restore_reserve_on_error(). Rename new_pagecache_page to
page_in_pagecache to make that clear.