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, 4 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index 7f6537b..d7805ac 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1222,7 +1222,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
 			goto invalid;
 	}
 
-	addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate);
+	addr = do_mmap_pgoff(file, addr, size, prot, flags, 0, &populate, NULL);
 	*raddr = addr;
 	err = 0;
 	if (IS_ERR_VALUE(addr))
@@ -1329,7 +1329,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
 			 */
 			file = vma->vm_file;
 			size = i_size_read(file_inode(vma->vm_file));
-			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
+			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
 			/*
 			 * We discovered the size of the shm segment, so
 			 * break out of here and fall through to the next
@@ -1356,7 +1356,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
 		if ((vma->vm_ops == &shm_vm_ops) &&
 		    ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
 		    (vma->vm_file == file))
-			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
+			do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
 		vma = next;
 	}
 
@@ -1365,7 +1365,7 @@ SYSCALL_DEFINE1(shmdt, char __user *, shmaddr)
 	 * given
 	 */
 	if (vma && vma->vm_start == addr && vma->vm_ops == &shm_vm_ops) {
-		do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start);
+		do_munmap(mm, vma->vm_start, vma->vm_end - vma->vm_start, NULL);
 		retval = 0;
 	}