uprobes: Flush cache after xol write

Flush the cache so that the instructions written to the XOL area are
visible.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 39c75cc..5ce99cf 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1199,6 +1199,11 @@
 	vaddr = kmap_atomic(area->page);
 	memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
 	kunmap_atomic(vaddr);
+	/*
+	 * We probably need flush_icache_user_range() but it needs vma.
+	 * This should work on supported architectures too.
+	 */
+	flush_dcache_page(area->page);
 
 	return current->utask->xol_vaddr;
 }