net: ena: fix driver when PAGE_SIZE == 64kB

BugLink: http://bugs.launchpad.net/bugs/1792044

The buffer length field in the ena rx descriptor is 16 bit, and the
current driver passes a full page in each ena rx descriptor.
When PAGE_SIZE equals 64kB or more, the buffer length field becomes
zero.
To solve this issue, limit the ena Rx descriptor to use 16kB even
when allocating 64kB kernel pages. This change would not impact ena
device functionality, as 16kB is still larger than maximum MTU.
Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit ef5b0771 linux-next)
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

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

@@ -468,7 +468,7 @@ static inline int ena_alloc_rx_page(struct ena_ring *rx_ring,
 		return -ENOMEM;
 	}
 
-	dma = dma_map_page(rx_ring->dev, page, 0, PAGE_SIZE,
+	dma = dma_map_page(rx_ring->dev, page, 0, ENA_PAGE_SIZE,
 			   DMA_FROM_DEVICE);
 	if (unlikely(dma_mapping_error(rx_ring->dev, dma))) {
 		u64_stats_update_begin(&rx_ring->syncp);
@@ -485,7 +485,7 @@ static inline int ena_alloc_rx_page(struct ena_ring *rx_ring,
 	rx_info->page_offset = 0;
 	ena_buf = &rx_info->ena_buf;
 	ena_buf->paddr = dma;
-	ena_buf->len = PAGE_SIZE;
+	ena_buf->len = ENA_PAGE_SIZE;
 
 	return 0;
 }
@@ -502,7 +502,7 @@ static void ena_free_rx_page(struct ena_ring *rx_ring,
 		return;
 	}
 
-	dma_unmap_page(rx_ring->dev, ena_buf->paddr, PAGE_SIZE,
+	dma_unmap_page(rx_ring->dev, ena_buf->paddr, ENA_PAGE_SIZE,
 		       DMA_FROM_DEVICE);
 
 	__free_page(page);
@@ -923,10 +923,10 @@ static struct sk_buff *ena_rx_skb(struct ena_ring *rx_ring,
 	do {
 		dma_unmap_page(rx_ring->dev,
 			       dma_unmap_addr(&rx_info->ena_buf, paddr),
-			       PAGE_SIZE, DMA_FROM_DEVICE);
+			       ENA_PAGE_SIZE, DMA_FROM_DEVICE);
 
 		skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags, rx_info->page,
-				rx_info->page_offset, len, PAGE_SIZE);
+				rx_info->page_offset, len, ENA_PAGE_SIZE);
 
 		netif_dbg(rx_ring->adapter, rx_status, rx_ring->netdev,
 			  "rx skb updated. len %d. data_len %d\n",

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

@@ -353,4 +353,15 @@ void ena_dump_stats_to_buf(struct ena_adapter *adapter, u8 *buf);
 
 int ena_get_sset_count(struct net_device *netdev, int sset);
 
+/* The ENA buffer length fields is 16 bit long. So when PAGE_SIZE == 64kB the
+ * driver passas 0.
+ * Since the max packet size the ENA handles is ~9kB limit the buffer length to
+ * 16kB.
+ */
+#if PAGE_SIZE > SZ_16K
+#define ENA_PAGE_SIZE SZ_16K
+#else
+#define ENA_PAGE_SIZE PAGE_SIZE
+#endif
+
 #endif /* !(ENA_H) */