vm_fault_copy_entry: accept invalid source pages.
Either msync(MS_INVALIDATE) or the object unlock during vnode
truncation can expose invalid pages backing wired entries. Accept
them, but do not install them into destrination pmap. We must create
copied pages in the copy case, because e.g. vm_object_unwire() expects
that the entry is fully backed.
Reported by: syzkaller, via emaste
Reported by: syzbot+514d40ce757a3f8b15bc at syzkaller.appspotmail.com
Reviewed by: markj
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D19615
UnifiedSplitRaw
