FROMLIST: mm: implement speculative handling in do_anonymous_page()

Change do_anonymous_page() to handle the speculative case.
This involves aborting speculative faults if they have to allocate a new
anon_vma, and using pte_map_lock() instead of pte_offset_map_lock()
to complete the page fault.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
Link: https://lore.kernel.org/all/20220128131006.67712-19-michel@lespinasse.org/


Bug: 161210518
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I5ad955323faabc142c21f62415db039ac889066a