mm: call invalidate_range_end in do_wp_page even for zero pages

mm: call invalidate_range_end in do_wp_page even for zero pages

The previous patch "mm: wrap calls to set_pte_at_notify with
invalidate_range_start and invalidate_range_end" only called the
invalidate_range_end mmu notifier function in do_wp_page when the new_page
variable wasn't NULL.  This was done in order to only call
invalidate_range_end after invalidate_range_start was called.
Unfortunately, there are situations where new_page is NULL and
invalidate_range_start is called.  This caused invalidate_range_start to
be called without a matching invalidate_range_end, causing kvm to loop
indefinitely on the first page fault.

This patch adds a flag variable to do_wp_page that marks whether the
invalidate_range_start notifier was called.  invalidate_range_end is then
called if the flag is true.

Reported-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Haggai Eran <haggaie@mellanox.com>
Cc: Andrea Arcangeli <andrea@qumranet.com>
Cc: Sagi Grimberg <sagig@mellanox.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Haggai Eran <haggaie@mellanox.com>
Cc: Shachar Raindel <raindel@mellanox.com>
Cc: Liran Liss <liranl@mellanox.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>