UPSTREAM: mm: handle COW faults under the VMA lock

If the page is not currently present in the page tables, we need to call
the page fault handler to find out which page we're supposed to COW, so we
need to both check that there is already an anon_vma and that the fault
handler doesn't need the mmap_lock.

Link: https://lkml.kernel.org/r/20231006195318.4087158-5-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
(cherry picked from commit 4de8c93a)

Bug: 293665307
Bug: 332639610
Change-Id: If749a6f8fcf69d83bbf872c1d45865d1b1b77ea0
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: fengqi <fengqi@xiaomi.corp-partner.google.com>