net/ena: use READ_ONCE to access completion descriptors

BugLink: http://bugs.launchpad.net/bugs/1664312

Completion descriptors are accessed from the driver and from the device.
To avoid reading the old value, use READ_ONCE macro.
Signed-off-by: Netanel Belgazal <netanel@annapurnalabs.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit a8496eb8)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/net/ethernet/amazon/ena/ena_com.h

@@ -33,6 +33,7 @@
 #ifndef ENA_COM
 #define ENA_COM
 
+#include <linux/compiler.h>
 #include <linux/delay.h>
 #include <linux/dma-mapping.h>
 #include <linux/gfp.h>

drivers/net/ethernet/amazon/ena/ena_eth_com.c

@@ -45,7 +45,7 @@ static inline struct ena_eth_io_rx_cdesc_base *ena_com_get_next_rx_cdesc(
 	cdesc = (struct ena_eth_io_rx_cdesc_base *)(io_cq->cdesc_addr.virt_addr
 			+ (head_masked * io_cq->cdesc_entry_size_in_bytes));
 
-	desc_phase = (cdesc->status & ENA_ETH_IO_RX_CDESC_BASE_PHASE_MASK) >>
+	desc_phase = (READ_ONCE(cdesc->status) & ENA_ETH_IO_RX_CDESC_BASE_PHASE_MASK) >>
 			ENA_ETH_IO_RX_CDESC_BASE_PHASE_SHIFT;
 
 	if (desc_phase != expected_phase)
@@ -141,7 +141,7 @@ static inline u16 ena_com_cdesc_rx_pkt_get(struct ena_com_io_cq *io_cq,
 
 		ena_com_cq_inc_head(io_cq);
 		count++;
-		last = (cdesc->status & ENA_ETH_IO_RX_CDESC_BASE_LAST_MASK) >>
+		last = (READ_ONCE(cdesc->status) & ENA_ETH_IO_RX_CDESC_BASE_LAST_MASK) >>
 			ENA_ETH_IO_RX_CDESC_BASE_LAST_SHIFT;
 	} while (!last);
 
@@ -489,13 +489,13 @@ int ena_com_tx_comp_req_id_get(struct ena_com_io_cq *io_cq, u16 *req_id)
 	 * expected, it mean that the device still didn't update
 	 * this completion.
 	 */
-	cdesc_phase = cdesc->flags & ENA_ETH_IO_TX_CDESC_PHASE_MASK;
+	cdesc_phase = READ_ONCE(cdesc->flags) & ENA_ETH_IO_TX_CDESC_PHASE_MASK;
 	if (cdesc_phase != expected_phase)
 		return -EAGAIN;
 
 	ena_com_cq_inc_head(io_cq);
 
-	*req_id = cdesc->req_id;
+	*req_id = READ_ONCE(cdesc->req_id);
 
 	return 0;
 }