userfaultfd: non-cooperative: add mremap() event

The event denotes that an area [start:end] moves to different location.
Length change isn't reported as "new" addresses, if they appear on the
uffd reader side they will not contain any data and the latter can just
zeromap them.

Waiting for the event ACK is also done outside of mmap sem, as for fork
event.

Link: http://lkml.kernel.org/r/20161216144821.5183-12-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>

1 files changed, 37 insertions, 0 deletions

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 27978f249016..68f978beefac 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -596,6 +596,43 @@ void dup_userfaultfd_complete(struct list_head *fcs)
 	}
 }
 
+void mremap_userfaultfd_prep(struct vm_area_struct *vma,
+			     struct vm_userfaultfd_ctx *vm_ctx)
+{
+	struct userfaultfd_ctx *ctx;
+
+	ctx = vma->vm_userfaultfd_ctx.ctx;
+	if (ctx && (ctx->features & UFFD_FEATURE_EVENT_REMAP)) {
+		vm_ctx->ctx = ctx;
+		userfaultfd_ctx_get(ctx);
+	}
+}
+
+void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx vm_ctx,
+				 unsigned long from, unsigned long to,
+				 unsigned long len)
+{
+	struct userfaultfd_ctx *ctx = vm_ctx.ctx;
+	struct userfaultfd_wait_queue ewq;
+
+	if (!ctx)
+		return;
+
+	if (to & ~PAGE_MASK) {
+		userfaultfd_ctx_put(ctx);
+		return;
+	}
+
+	msg_init(&ewq.msg);
+
+	ewq.msg.event = UFFD_EVENT_REMAP;
+	ewq.msg.arg.remap.from = from;
+	ewq.msg.arg.remap.to = to;
+	ewq.msg.arg.remap.len = len;
+
+	userfaultfd_event_wait_completion(ctx, &ewq);
+}
+
 static int userfaultfd_release(struct inode *inode, struct file *file)
 {
 	struct userfaultfd_ctx *ctx = file->private_data;