diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index ba488a36dca0..2a9327f5c14c 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -528,35 +528,6 @@ static bool mptcp_check_data_fin(struct sock *sk)
 	return ret;
 }
 
-static bool mptcp_validate_data_checksum(struct sock *ssk)
-{
-	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
-	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
-	struct csum_pseudo_header header;
-	__wsum csum;
-
-	if (__mptcp_check_fallback(msk))
-		goto out;
-
-	if (subflow->csum_len < subflow->map_data_len)
-		goto out;
-
-	header.data_seq = subflow->map_seq;
-	header.subflow_seq = subflow->map_subflow_seq;
-	header.data_len = subflow->map_data_len;
-	header.csum = subflow->map_csum;
-
-	csum = csum_partial(&header, sizeof(header), subflow->data_csum);
-
-	if (csum_fold(csum))
-		return false;
-	subflow->data_csum = 0;
-	subflow->csum_len = 0;
-
-out:
-	return true;
-}
-
 static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 					   struct sock *ssk,
 					   unsigned int *bytes)
@@ -625,12 +596,6 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
 			if (tp->urg_data)
 				done = true;
 
-			if (READ_ONCE(msk->csum_enabled)) {
-				subflow->data_csum = skb_checksum(skb, offset, len,
-								  subflow->data_csum);
-				subflow->csum_len += len;
-				mptcp_validate_data_checksum(ssk);
-			}
 			if (__mptcp_move_skb(msk, ssk, skb, offset, len))
 				moved += len;
 			seq += len;
@@ -1320,7 +1285,7 @@ static bool mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk)
 static void mptcp_update_data_checksum(struct sk_buff *skb, int added)
 {
 	struct mptcp_ext *mpext = mptcp_get_ext(skb);
-	__wsum csum = csum_unfold(mpext->csum);
+	__wsum csum = ~csum_unfold(mpext->csum);
 	int offset = skb->len - added;
 
 	mpext->csum = csum_fold(csum_block_add(csum, skb_checksum(skb, offset, added, 0), offset));
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index f1d9657eb6ce..39ba2efc60e9 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -399,9 +399,8 @@ struct mptcp_subflow_context {
 	u32	map_subflow_seq;
 	u32	ssn_offset;
 	u32	map_data_len;
-	__wsum	data_csum;
-	u32	csum_len;
-	__sum16	map_csum;
+	__wsum	map_data_csum;
+	u32	map_csum_len;
 	u32	request_mptcp : 1,  /* send MP_CAPABLE */
 		request_join : 1,   /* send MP_JOIN */
 		request_bkup : 1,
@@ -411,6 +410,8 @@ struct mptcp_subflow_context {
 		pm_notified : 1,    /* PM hook called for established status */
 		conn_finished : 1,
 		map_valid : 1,
+		map_csum_reqd : 1,
+		map_data_fin : 1,
 		mpc_map : 1,
 		backup : 1,
 		send_mp_prio : 1,
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 8648d25190e1..2d7579ba1536 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -829,10 +829,90 @@ static bool validate_mapping(struct sock *ssk, struct sk_buff *skb)
 	return true;
 }
 
+static enum mapping_status validate_data_csum(struct sock *ssk, struct sk_buff *skb,
+					      bool csum_reqd)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	struct csum_pseudo_header header;
+	u32 offset, seq, delta;
+	__wsum csum;
+	int len;
+
+	if (!csum_reqd)
+		return MAPPING_OK;
+
+	/* mapping already validated on previous traversal */
+	if (subflow->map_csum_len == subflow->map_data_len)
+		return MAPPING_OK;
+
+	/* traverse the receive queue, ensuring it contains a full
+	 * DSS mapping and accumulating the related csum.
+	 * Preserve the accoumlate csum across multiple calls, to compute
+	 * the csum only once
+	 */
+	delta = subflow->map_data_len - subflow->map_csum_len;
+	for (;;) {
+		seq = tcp_sk(ssk)->copied_seq + subflow->map_csum_len;
+		offset = seq - TCP_SKB_CB(skb)->seq;
+
+		/* if the current skb has not been accounted yet, csum its contents
+		 * up to the amount covered by the current DSS
+		 */
+		if (offset < skb->len) {
+			__wsum csum;
+
+			len = min(skb->len - offset, delta);
+			csum = skb_checksum(skb, offset, len, 0);
+			subflow->map_data_csum = csum_block_add(subflow->map_data_csum, csum,
+								subflow->map_csum_len);
+
+			delta -= len;
+			subflow->map_csum_len += len;
+		}
+		if (delta == 0)
+			break;
+
+		if (skb_queue_is_last(&ssk->sk_receive_queue, skb)) {
+			/* if this subflow is closed, the partial mapping
+			 * will be never completed; flush the pending skbs, so
+			 * that subflow_sched_work_if_closed() can kick in
+			 */
+			if (unlikely(ssk->sk_state == TCP_CLOSE))
+				while ((skb = skb_peek(&ssk->sk_receive_queue)))
+					sk_eat_skb(ssk, skb);
+
+			/* not enough data to validate the csum */
+			return MAPPING_EMPTY;
+		}
+
+		/* the DSS mapping for next skbs will be validated later,
+		 * when a get_mapping_status call will process such skb
+		 */
+		skb = skb->next;
+	}
+
+	/* note that 'map_data_len' accounts only for the carried data, does
+	 * not include the eventual seq increment due to the data fin,
+	 * while the pseudo header requires the original DSS data len,
+	 * including that
+	 */
+	header.data_seq = cpu_to_be64(subflow->map_seq);
+	header.subflow_seq = htonl(subflow->map_subflow_seq);
+	header.data_len = htons(subflow->map_data_len + subflow->map_data_fin);
+	header.csum = 0;
+
+	csum = csum_partial(&header, sizeof(header), subflow->map_data_csum);
+	if (unlikely(csum_fold(csum)))
+		return subflow->mp_join ? MAPPING_INVALID : MAPPING_DUMMY;
+
+	return MAPPING_OK;
+}
+
 static enum mapping_status get_mapping_status(struct sock *ssk,
 					      struct mptcp_sock *msk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
+	bool csum_reqd = READ_ONCE(msk->csum_enabled);
 	struct mptcp_ext *mpext;
 	struct sk_buff *skb;
 	u16 data_len;
@@ -926,9 +1006,10 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 		/* Allow replacing only with an identical map */
 		if (subflow->map_seq == map_seq &&
 		    subflow->map_subflow_seq == mpext->subflow_seq &&
-		    subflow->map_data_len == data_len) {
+		    subflow->map_data_len == data_len &&
+		    subflow->map_csum_reqd == mpext->csum_reqd) {
 			skb_ext_del(skb, SKB_EXT_MPTCP);
-			return MAPPING_OK;
+			goto validate_csum;
 		}
 
 		/* If this skb data are fully covered by the current mapping,
@@ -940,20 +1021,27 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 		}
 
 		/* will validate the next map after consuming the current one */
-		return MAPPING_OK;
+		goto validate_csum;
 	}
 
 	subflow->map_seq = map_seq;
 	subflow->map_subflow_seq = mpext->subflow_seq;
 	subflow->map_data_len = data_len;
 	subflow->map_valid = 1;
+	subflow->map_data_fin = mpext->data_fin;
 	subflow->mpc_map = mpext->mpc_map;
-	subflow->data_csum = 0;
-	subflow->csum_len = 0;
-	subflow->map_csum = mpext->csum;
-	pr_debug("new map seq=%llu subflow_seq=%u data_len=%u csum=%u",
+	subflow->map_csum_reqd = mpext->csum_reqd;
+	subflow->map_csum_len = 0;
+	subflow->map_data_csum = csum_unfold(mpext->csum);
+
+	/* Cfr RFC 8684 Section 3.3.0 */
+	if (unlikely(subflow->map_csum_reqd != csum_reqd))
+		return MAPPING_INVALID;
+
+	pr_debug("new map seq=%llu subflow_seq=%u data_len=%u csum=%d:%u",
 		 subflow->map_seq, subflow->map_subflow_seq,
-		 subflow->map_data_len, subflow->map_csum);
+		 subflow->map_data_len, subflow->map_csum_reqd,
+		 subflow->map_data_csum);
 
 validate_seq:
 	/* we revalidate valid mapping on new skb, because we must ensure
@@ -963,7 +1051,9 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 		return MAPPING_INVALID;
 
 	skb_ext_del(skb, SKB_EXT_MPTCP);
-	return MAPPING_OK;
+
+validate_csum:
+	return validate_data_csum(ssk, skb, csum_reqd);
 }
 
 static void mptcp_subflow_discard_data(struct sock *ssk, struct sk_buff *skb,
