KVM: x86: add track_flush_slot page track notifier

When a memory slot is being moved or removed users of page track
can be notified. So users can drop write-protection for the pages
in that memory slot.

This notifier type is needed by KVMGT to sync up its shadow page
table when memory slot is being moved or removed.

Register the notifier type track_flush_slot to receive memslot move
and remove event.

Reviewed-by: Xiao Guangrong <guangrong.xiao@intel.com>
Signed-off-by: Chen Xiaoguang <xiaoguang.chen@intel.com>
[Squashed commits to avoid bisection breakage and reworded the subject.]
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/kvm/page_track.c

@@ -225,3 +225,28 @@ void kvm_page_track_write(struct kvm_vcpu *vcpu, gpa_t gpa, const u8 *new,
 			n->track_write(vcpu, gpa, new, bytes);
 	srcu_read_unlock(&head->track_srcu, idx);
 }
+
+/*
+ * Notify the node that memory slot is being removed or moved so that it can
+ * drop write-protection for the pages in the memory slot.
+ *
+ * The node should figure out it has any write-protected pages in this slot
+ * by itself.
+ */
+void kvm_page_track_flush_slot(struct kvm *kvm, struct kvm_memory_slot *slot)
+{
+	struct kvm_page_track_notifier_head *head;
+	struct kvm_page_track_notifier_node *n;
+	int idx;
+
+	head = &kvm->arch.track_notifier_head;
+
+	if (hlist_empty(&head->track_notifier_list))
+		return;
+
+	idx = srcu_read_lock(&head->track_srcu);
+	hlist_for_each_entry_rcu(n, &head->track_notifier_list, node)
+		if (n->track_flush_slot)
+			n->track_flush_slot(kvm, slot);
+	srcu_read_unlock(&head->track_srcu, idx);
+}