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, 4 insertions, 1 deletions

diff --git a/mm/util.c b/mm/util.c
index 3cb2164f4099..b8f538863b5a 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -11,6 +11,7 @@
 #include <linux/mman.h>
 #include <linux/hugetlb.h>
 #include <linux/vmalloc.h>
+#include <linux/userfaultfd_k.h>
 
 #include <asm/sections.h>
 #include <linux/uaccess.h>
@@ -297,14 +298,16 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr,
         unsigned long ret;
         struct mm_struct *mm = current->mm;
         unsigned long populate;
+        LIST_HEAD(uf);
 
         ret = security_mmap_file(file, prot, flag);
         if (!ret) {
                 if (down_write_killable(&mm->mmap_sem))
                         return -EINTR;
                 ret = do_mmap_pgoff(file, addr, len, prot, flag, pgoff,
-                                    &populate);
+                                    &populate, &uf);
                 up_write(&mm->mmap_sem);
+                userfaultfd_unmap_complete(mm, &uf);
                 if (populate)
                         mm_populate(ret, populate);
         }