userfaultfd: non-cooperative: add event for memory unmaps

When a non-cooperative userfaultfd monitor copies pages in the
background, it may encounter regions that were already unmapped.
Addition of UFFD_EVENT_UNMAP allows the uffd monitor to track precisely
changes in the virtual memory layout.

Since there might be different uffd contexts for the affected VMAs, we
first should create a temporary representation for the unmap event for
each uffd context and then notify them one by one to the appropriate
userfault file descriptors.

The event notification occurs after the mmap_sem has been released.

[arnd@arndb.de: fix nommu build]
  Link: http://lkml.kernel.org/r/20170203165141.3665284-1-arnd@arndb.de
[mhocko@suse.com: fix nommu build]
  Link: http://lkml.kernel.org/r/20170202091503.GA22823@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/1485542673-24387-3-git-send-email-rppt@linux.vnet.ibm.com
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 2 deletions

diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index aad4ac386f98..c98079684bdb 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -51,7 +51,7 @@ static unsigned long mpx_mmap(unsigned long len)
 
         down_write(&mm->mmap_sem);
         addr = do_mmap(NULL, 0, len, PROT_READ | PROT_WRITE,
-                        MAP_ANONYMOUS | MAP_PRIVATE, VM_MPX, 0, &populate);
+                       MAP_ANONYMOUS | MAP_PRIVATE, VM_MPX, 0, &populate, NULL);
         up_write(&mm->mmap_sem);
         if (populate)
                 mm_populate(addr, populate);
@@ -893,7 +893,7 @@ static int unmap_entire_bt(struct mm_struct *mm,
          * avoid recursion, do_munmap() will check whether it comes
          * from one bounds table through VM_MPX flag.
          */
-        return do_munmap(mm, bt_addr, mpx_bt_size_bytes(mm));
+        return do_munmap(mm, bt_addr, mpx_bt_size_bytes(mm), NULL);
 }
 
 static int try_unmap_single_bt(struct mm_struct *mm,