diff --git a/vhost-user-backend/README.md b/vhost-user-backend/README.md
index a4e51a8..46b771c 100644
--- a/vhost-user-backend/README.md
+++ b/vhost-user-backend/README.md
@@ -98,6 +98,16 @@ impl VhostUserBackendMut for VhostUserService {
 }
 ```
 
+## Postcopy support
+
+To enabled POSTCOPY_* messages support there is a `postcopy` feature.
+Due to how Xen handles memory mappings the `postcopy` feature is not compatible
+with `xen` feature. Enabling both at the same time will result in a compilation error.
+
+`postcopy` feature enables optional `userfaultfd` dependency in order to create and
+interact with `userfaultfd` object. This requires access permission to `/dev/userfaultfd`
+file from the backend.
+
 ## Xen support
 
 Supporting Xen requires special handling while mapping the guest memory. The
diff --git a/vhost/README.md b/vhost/README.md
index 1eef3f4..101b4d7 100644
--- a/vhost/README.md
+++ b/vhost/README.md
@@ -31,6 +31,12 @@ Frontend is the application that shares its virtqueues, backend is the consumer
 of the virtqueues. Frontend and backend can be either a client (i.e. connecting)
 or server (listening) in the socket communication.
 
+## Postcopy support
+
+To enabled POSTCOPY_* messages support there is a `postcopy` feature.
+Due to how Xen handles memory mappings the `postcopy` feature is not compatible
+with `xen` feature. Enabling both at the same time will result in a compilation error.
+
 ## Xen support
 
 Supporting Xen requires special handling while mapping the guest memory. The