mm/swap: fix pte_same_as_swp() not removing uffd-wp bit when compare

stable inclusion
from stable-5.10.46
commit 12eb3c2c1a4f6e7c30de2aa0a09cb1b9e19fa9c0
bugzilla: 168323
CVE: NA

--------------------------------

commit 099dd687 upstream.

I found it by pure code review, that pte_same_as_swp() of unuse_vma()
didn't take uffd-wp bit into account when comparing ptes.
pte_same_as_swp() returning false negative could cause failure to
swapoff swap ptes that was wr-protected by userfaultfd.

Link: https://lkml.kernel.org/r/20210603180546.9083-1-peterx@redhat.com


Fixes: f45ec5ff ("userfaultfd: wp: support swap and page migration")
Signed-off-by: Peter Xu <peterx@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>	[5.7+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>