[PATCH 4.9 06/45] ibmvnic: Ensure that SCRQ entry reads are correctly ordered

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Thomas Falcon <tlfalcon@linux.ibm.com>

[ Upstream commit b71ec952234610b4f90ef17a2fdcb124d5320070 ]

Ensure that received Subordinate Command-Response Queue (SCRQ)
entries are properly read in order by the driver. These queues
are used in the ibmvnic device to process RX buffer and TX completion
descriptors. dma_rmb barriers have been added after checking for a
pending descriptor to ensure the correct descriptor entry is checked
and after reading the SCRQ descriptor to ensure the entire
descriptor is read before processing.

Fixes: 032c5e82847a ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/ibm/ibmvnic.c |   18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -985,6 +985,12 @@ restart_poll:
 
 		if (!pending_scrq(adapter, adapter->rx_scrq[scrq_num]))
 			break;
+		/* The queue entry at the current index is peeked at above
+		 * to determine that there is a valid descriptor awaiting
+		 * processing. We want to be sure that the current slot
+		 * holds a valid descriptor before reading its contents.
+		 */
+		dma_rmb();
 		next = ibmvnic_next_scrq(adapter, adapter->rx_scrq[scrq_num]);
 		rx_buff =
 		    (struct ibmvnic_rx_buff *)be64_to_cpu(next->
@@ -1373,6 +1379,13 @@ restart_loop:
 	while (pending_scrq(adapter, scrq)) {
 		unsigned int pool = scrq->pool_index;
 
+		/* The queue entry at the current index is peeked at above
+		 * to determine that there is a valid descriptor awaiting
+		 * processing. We want to be sure that the current slot
+		 * holds a valid descriptor before reading its contents.
+		 */
+		dma_rmb();
+
 		next = ibmvnic_next_scrq(adapter, scrq);
 		for (i = 0; i < next->tx_comp.num_comps; i++) {
 			if (next->tx_comp.rcs[i]) {
@@ -1707,6 +1720,11 @@ static union sub_crq *ibmvnic_next_scrq(
 	}
 	spin_unlock_irqrestore(&scrq->lock, flags);
 
+	/* Ensure that the entire buffer descriptor has been
+	 * loaded before reading its contents
+	 */
+	dma_rmb();
+
 	return entry;
 }