userfaultfd: non-cooperative: Add fork() event
authorPavel Emelyanov <xemul@parallels.com>
Wed, 22 Feb 2017 23:42:27 +0000 (15:42 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Thu, 23 Feb 2017 00:41:28 +0000 (16:41 -0800)
commit893e26e61d04eac974ded0c11e1647b335c8cb7b
treed75bbbd621a08130e8794dffcedc71f4a6ff50cc
parent656031445d5a855e1c13b291dedae32579d0f3f2
userfaultfd: non-cooperative: Add fork() event

When the mm with uffd-ed vmas fork()-s the respective vmas notify their
uffds with the event which contains a descriptor with new uffd.  This
new descriptor can then be used to get events from the child and
populate its mm with data.  Note, that there can be different uffd-s
controlling different vmas within one mm, so first we should collect all
those uffds (and ctx-s) in a list and then notify them all one by one
but only once per fork().

The context is created at fork() time but the descriptor, file struct
and anon inode object is created at event read time.  So some trickery
is added to the userfaultfd_ctx_read() to handle the ctx queues' locking
vs file creation.

Another thing worth noticing is that the task that fork()-s waits for
the uffd event to get processed WITHOUT the mmap sem.

[aarcange@redhat.com: build warning fix]
Link: http://lkml.kernel.org/r/20161216144821.5183-10-aarcange@redhat.com
Link: http://lkml.kernel.org/r/20161216144821.5183-9-aarcange@redhat.com
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
fs/userfaultfd.c
include/linux/userfaultfd_k.h
include/uapi/linux/userfaultfd.h
kernel/fork.c