diff --git a/Documentation/networking/rxrpc.txt b/Documentation/networking/rxrpc.txt
index bce8e10a2a8e..8c70ba5dee4d 100644
--- a/Documentation/networking/rxrpc.txt
+++ b/Documentation/networking/rxrpc.txt
@@ -327,6 +327,7 @@ calls, to invoke certain actions and to report certain conditions.  These are:
 	RXRPC_ACCEPT		s-- n/a		Accept new call
 	RXRPC_EXCLUSIVE_CALL	s-- n/a		Make an exclusive client call
 	RXRPC_UPGRADE_SERVICE	s-- n/a		Client call can be upgraded
+	RXRPC_TX_LENGTH		s-- data len	Total length of Tx data
 
 	(SRT = usable in Sendmsg / delivered by Recvmsg / Terminal message)
 
@@ -406,6 +407,19 @@ calls, to invoke certain actions and to report certain conditions.  These are:
      future communication to that server and RXRPC_UPGRADE_SERVICE should no
      longer be set.
 
+ (*) RXRPC_TX_LENGTH
+
+     This is used to inform the kernel of the total amount of data that is
+     going to be transmitted by a call (whether in a client request or a
+     service response).  If given, it allows the kernel to encrypt from the
+     userspace buffer directly to the packet buffers, rather than copying into
+     the buffer and then encrypting in place.  This may only be given with the
+     first sendmsg() providing data for a call.  EMSGSIZE will be generated if
+     the amount of data actually given is different.
+
+     This takes a parameter of __s64 type that indicates how much will be
+     transmitted.  This may not be less than zero.
+
 The symbol RXRPC__SUPPORTED is defined as one more than the highest control
 message type supported.  At run time this can be queried by means of the
 RXRPC_SUPPORTED_CMSG socket option (see below).
@@ -577,6 +591,9 @@ A client would issue an operation by:
      MSG_MORE should be set in msghdr::msg_flags on all but the last part of
      the request.  Multiple requests may be made simultaneously.
 
+     An RXRPC_TX_LENGTH control message can also be specified on the first
+     sendmsg() call.
+
      If a call is intended to go to a destination other than the default
      specified through connect(), then msghdr::msg_name should be set on the
      first request message of that call.
@@ -764,6 +781,7 @@ The kernel interface functions are as follows:
 				struct sockaddr_rxrpc *srx,
 				struct key *key,
 				unsigned long user_call_ID,
+				s64 tx_total_len,
 				gfp_t gfp);
 
      This allocates the infrastructure to make a new RxRPC call and assigns
@@ -780,6 +798,11 @@ The kernel interface functions are as follows:
      control data buffer.  It is entirely feasible to use this to point to a
      kernel data structure.
 
+     tx_total_len is the amount of data the caller is intending to transmit
+     with this call (or -1 if unknown at this point).  Setting the data size
+     allows the kernel to encrypt directly to the packet buffers, thereby
+     saving a copy.  The value may not be less than -1.
+
      If this function is successful, an opaque reference to the RxRPC call is
      returned.  The caller now holds a reference on this and it must be
      properly ended.
@@ -931,6 +954,17 @@ The kernel interface functions are as follows:
 
      This is used to find the remote peer address of a call.
 
+ (*) Set the total transmit data size on a call.
+
+	void rxrpc_kernel_set_tx_length(struct socket *sock,
+					struct rxrpc_call *call,
+					s64 tx_total_len);
+
+     This sets the amount of data that the caller is intending to transmit on a
+     call.  It's intended to be used for setting the reply size as the request
+     size should be set when the call is begun.  tx_total_len may not be less
+     than zero.
+
 
 =======================
 CONFIGURABLE PARAMETERS
diff --git a/fs/afs/rxrpc.c b/fs/afs/rxrpc.c
index d5990eb160bd..02781e78ffb6 100644
--- a/fs/afs/rxrpc.c
+++ b/fs/afs/rxrpc.c
@@ -341,6 +341,7 @@ int afs_make_call(struct in_addr *addr, struct afs_call *call, gfp_t gfp,
 	struct msghdr msg;
 	struct kvec iov[1];
 	size_t offset;
+	s64 tx_total_len;
 	u32 abort_code;
 	int ret;
 
@@ -364,9 +365,20 @@ int afs_make_call(struct in_addr *addr, struct afs_call *call, gfp_t gfp,
 	srx.transport.sin.sin_port = call->port;
 	memcpy(&srx.transport.sin.sin_addr, addr, 4);
 
+	/* Work out the length we're going to transmit.  This is awkward for
+	 * calls such as FS.StoreData where there's an extra injection of data
+	 * after the initial fixed part.
+	 */
+	tx_total_len = call->request_size;
+	if (call->send_pages) {
+		tx_total_len += call->last_to - call->first_offset;
+		tx_total_len += (call->last - call->first) * PAGE_SIZE;
+	}
+
 	/* create a call */
 	rxcall = rxrpc_kernel_begin_call(afs_socket, &srx, call->key,
-					 (unsigned long) call, gfp,
+					 (unsigned long)call,
+					 tx_total_len, gfp,
 					 (async ?
 					  afs_wake_up_async_call :
 					  afs_wake_up_call_waiter));
@@ -738,6 +750,8 @@ void afs_send_empty_reply(struct afs_call *call)
 
 	_enter("");
 
+	rxrpc_kernel_set_tx_length(afs_socket, call->rxcall, 0);
+
 	msg.msg_name		= NULL;
 	msg.msg_namelen		= 0;
 	iov_iter_kvec(&msg.msg_iter, WRITE | ITER_KVEC, NULL, 0, 0);
@@ -772,6 +786,8 @@ void afs_send_simple_reply(struct afs_call *call, const void *buf, size_t len)
 
 	_enter("");
 
+	rxrpc_kernel_set_tx_length(afs_socket, call->rxcall, len);
+
 	iov[0].iov_base		= (void *) buf;
 	iov[0].iov_len		= len;
 	msg.msg_name		= NULL;
diff --git a/include/linux/rxrpc.h b/include/linux/rxrpc.h
index bdd3175b9a48..7343f71783dc 100644
--- a/include/linux/rxrpc.h
+++ b/include/linux/rxrpc.h
@@ -57,6 +57,7 @@ enum rxrpc_cmsg_type {
 	RXRPC_ACCEPT		= 9,	/* s-: [Service] accept request */
 	RXRPC_EXCLUSIVE_CALL	= 10,	/* s-: Call should be on exclusive connection */
 	RXRPC_UPGRADE_SERVICE	= 11,	/* s-: Request service upgrade for client call */
+	RXRPC_TX_LENGTH		= 12,	/* s-: Total length of Tx data */
 	RXRPC__SUPPORTED
 };
 
diff --git a/include/net/af_rxrpc.h b/include/net/af_rxrpc.h
index b5f5187f488c..c172709787af 100644
--- a/include/net/af_rxrpc.h
+++ b/include/net/af_rxrpc.h
@@ -33,6 +33,7 @@ struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *,
 					   struct sockaddr_rxrpc *,
 					   struct key *,
 					   unsigned long,
+					   s64,
 					   gfp_t,
 					   rxrpc_notify_rx_t);
 int rxrpc_kernel_send_data(struct socket *, struct rxrpc_call *,
@@ -46,5 +47,6 @@ void rxrpc_kernel_get_peer(struct socket *, struct rxrpc_call *,
 			   struct sockaddr_rxrpc *);
 int rxrpc_kernel_charge_accept(struct socket *, rxrpc_notify_rx_t,
 			       rxrpc_user_attach_call_t, unsigned long, gfp_t);
+void rxrpc_kernel_set_tx_length(struct socket *, struct rxrpc_call *, s64);
 
 #endif /* _NET_RXRPC_H */
diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 44a52b82bb5d..58ae0db52ea1 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -262,6 +262,7 @@ static int rxrpc_listen(struct socket *sock, int backlog)
  * @srx: The address of the peer to contact
  * @key: The security context to use (defaults to socket setting)
  * @user_call_ID: The ID to use
+ * @tx_total_len: Total length of data to transmit during the call (or -1)
  * @gfp: The allocation constraints
  * @notify_rx: Where to send notifications instead of socket queue
  *
@@ -276,6 +277,7 @@ struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 					   struct sockaddr_rxrpc *srx,
 					   struct key *key,
 					   unsigned long user_call_ID,
+					   s64 tx_total_len,
 					   gfp_t gfp,
 					   rxrpc_notify_rx_t notify_rx)
 {
@@ -303,7 +305,8 @@ struct rxrpc_call *rxrpc_kernel_begin_call(struct socket *sock,
 	cp.security_level	= 0;
 	cp.exclusive		= false;
 	cp.service_id		= srx->srx_service;
-	call = rxrpc_new_client_call(rx, &cp, srx, user_call_ID, gfp);
+	call = rxrpc_new_client_call(rx, &cp, srx, user_call_ID, tx_total_len,
+				     gfp);
 	/* The socket has been unlocked. */
 	if (!IS_ERR(call))
 		call->notify_rx = notify_rx;
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index e9b536cb0acf..adbf37946450 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -528,6 +528,7 @@ struct rxrpc_call {
 	struct rb_node		sock_node;	/* Node in rx->calls */
 	struct sk_buff		*tx_pending;	/* Tx socket buffer being filled */
 	wait_queue_head_t	waitq;		/* Wait queue for channel or Tx */
+	s64			tx_total_len;	/* Total length left to be transmitted (or -1) */
 	__be32			crypto_buf[2];	/* Temporary packet crypto buffer */
 	unsigned long		user_call_ID;	/* user-defined call ID */
 	unsigned long		flags;
@@ -683,7 +684,7 @@ struct rxrpc_call *rxrpc_alloc_call(gfp_t);
 struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *,
 					 struct rxrpc_conn_parameters *,
 					 struct sockaddr_rxrpc *,
-					 unsigned long, gfp_t);
+					 unsigned long, s64, gfp_t);
 void rxrpc_incoming_call(struct rxrpc_sock *, struct rxrpc_call *,
 			 struct sk_buff *);
 void rxrpc_release_call(struct rxrpc_sock *, struct rxrpc_call *);
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index 692110808baa..423030fd93be 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -127,6 +127,7 @@ struct rxrpc_call *rxrpc_alloc_call(gfp_t gfp)
 	rwlock_init(&call->state_lock);
 	atomic_set(&call->usage, 1);
 	call->debug_id = atomic_inc_return(&rxrpc_debug_id);
+	call->tx_total_len = -1;
 
 	memset(&call->sock_node, 0xed, sizeof(call->sock_node));
 
@@ -201,6 +202,7 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
 					 struct rxrpc_conn_parameters *cp,
 					 struct sockaddr_rxrpc *srx,
 					 unsigned long user_call_ID,
+					 s64 tx_total_len,
 					 gfp_t gfp)
 	__releases(&rx->sk.sk_lock.slock)
 {
@@ -219,6 +221,7 @@ struct rxrpc_call *rxrpc_new_client_call(struct rxrpc_sock *rx,
 		return call;
 	}
 
+	call->tx_total_len = tx_total_len;
 	trace_rxrpc_call(call, rxrpc_call_new_client, atomic_read(&call->usage),
 			 here, (const void *)user_call_ID);
 
diff --git a/net/rxrpc/sendmsg.c b/net/rxrpc/sendmsg.c
index d939a5b1abc3..2e636a525a65 100644
--- a/net/rxrpc/sendmsg.c
+++ b/net/rxrpc/sendmsg.c
@@ -29,6 +29,7 @@ enum rxrpc_command {
 };
 
 struct rxrpc_send_params {
+	s64			tx_total_len;	/* Total Tx data length (if send data) */
 	unsigned long		user_call_ID;	/* User's call ID */
 	u32			abort_code;	/* Abort code to Tx (if abort) */
 	enum rxrpc_command	command : 8;	/* The command to implement */
@@ -207,6 +208,13 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 
 	more = msg->msg_flags & MSG_MORE;
 
+	if (call->tx_total_len != -1) {
+		if (len > call->tx_total_len)
+			return -EMSGSIZE;
+		if (!more && len != call->tx_total_len)
+			return -EMSGSIZE;
+	}
+
 	skb = call->tx_pending;
 	call->tx_pending = NULL;
 	rxrpc_see_skb(skb, rxrpc_skb_tx_seen);
@@ -299,6 +307,8 @@ static int rxrpc_send_data(struct rxrpc_sock *rx,
 			sp->remain -= copy;
 			skb->mark += copy;
 			copied += copy;
+			if (call->tx_total_len != -1)
+				call->tx_total_len -= copy;
 		}
 
 		/* check for the far side aborting the call or a network error
@@ -436,6 +446,14 @@ static int rxrpc_sendmsg_cmsg(struct msghdr *msg, struct rxrpc_send_params *p)
 				return -EINVAL;
 			break;
 
+		case RXRPC_TX_LENGTH:
+			if (p->tx_total_len != -1 || len != sizeof(__s64))
+				return -EINVAL;
+			p->tx_total_len = *(__s64 *)CMSG_DATA(cmsg);
+			if (p->tx_total_len < 0)
+				return -EINVAL;
+			break;
+
 		default:
 			return -EINVAL;
 		}
@@ -443,6 +461,8 @@ static int rxrpc_sendmsg_cmsg(struct msghdr *msg, struct rxrpc_send_params *p)
 
 	if (!got_user_ID)
 		return -EINVAL;
+	if (p->tx_total_len != -1 && p->command != RXRPC_CMD_SEND_DATA)
+		return -EINVAL;
 	_leave(" = 0");
 	return 0;
 }
@@ -481,7 +501,8 @@ rxrpc_new_client_call_for_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg,
 	cp.exclusive		= rx->exclusive | p->exclusive;
 	cp.upgrade		= p->upgrade;
 	cp.service_id		= srx->srx_service;
-	call = rxrpc_new_client_call(rx, &cp, srx, p->user_call_ID, GFP_KERNEL);
+	call = rxrpc_new_client_call(rx, &cp, srx, p->user_call_ID,
+				     p->tx_total_len, GFP_KERNEL);
 	/* The socket is now unlocked */
 
 	_leave(" = %p\n", call);
@@ -501,6 +522,7 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
 	int ret;
 
 	struct rxrpc_send_params p = {
+		.tx_total_len	= -1,
 		.user_call_ID	= 0,
 		.abort_code	= 0,
 		.command	= RXRPC_CMD_SEND_DATA,
@@ -555,6 +577,15 @@ int rxrpc_do_sendmsg(struct rxrpc_sock *rx, struct msghdr *msg, size_t len)
 			ret = -ERESTARTSYS;
 			goto error_put;
 		}
+
+		if (p.tx_total_len != -1) {
+			ret = -EINVAL;
+			if (call->tx_total_len != -1 ||
+			    call->tx_pending ||
+			    call->tx_top != 0)
+				goto error_put;
+			call->tx_total_len = p.tx_total_len;
+		}
 	}
 
 	state = READ_ONCE(call->state);
@@ -672,5 +703,24 @@ bool rxrpc_kernel_abort_call(struct socket *sock, struct rxrpc_call *call,
 	mutex_unlock(&call->user_mutex);
 	return aborted;
 }
-
 EXPORT_SYMBOL(rxrpc_kernel_abort_call);
+
+/**
+ * rxrpc_kernel_set_tx_length - Set the total Tx length on a call
+ * @sock: The socket the call is on
+ * @call: The call to be informed
+ * @tx_total_len: The amount of data to be transmitted for this call
+ *
+ * Allow a kernel service to set the total transmit length on a call.  This
+ * allows buffer-to-packet encrypt-and-copy to be performed.
+ *
+ * This function is primarily for use for setting the reply length since the
+ * request length can be set when beginning the call.
+ */
+void rxrpc_kernel_set_tx_length(struct socket *sock, struct rxrpc_call *call,
+				s64 tx_total_len)
+{
+	WARN_ON(call->tx_total_len != -1);
+	call->tx_total_len = tx_total_len;
+}
+EXPORT_SYMBOL(rxrpc_kernel_set_tx_length);