amd-xgbe: Fix race between access of desc and desc index

During Tx cleanup it's still possible for the descriptor data to be
read ahead of the descriptor index. A memory barrier is required between
the read of the descriptor index and the start of the Tx cleanup loop.
This allows a change to a lighter-weight barrier in the Tx transmit
routine just before updating the current descriptor index.

Since the memory barrier does result in extra overhead on arm64, keep
the previous change to not chase the current descriptor value. This
prevents the execution of the barrier for each loop performed.

Suggested-by: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
index e9ab8b9f3b9cb8835f7df479a75f9e94666d608b..f672dba345f7f73b028741ec60befa6ab012fd04 100644 (file)
--- a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c
@@ -1595,7 +1595,7 @@ static void xgbe_dev_xmit(struct xgbe_channel *channel)
                                  packet->rdesc_count, 1);
 
        /* Make sure ownership is written to the descriptor */
-       wmb();
+       smp_wmb();
 
        ring->cur = cur_index + 1;
        if (!packet->skb->xmit_more ||

diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
index d2b77d985441f2b1e82889db57eaca6ae133cc55..dde0486667e0cfab87c593283d80a71f873977d3 100644 (file)
--- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
+++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c
@@ -1816,6 +1816,10 @@ static int xgbe_tx_poll(struct xgbe_channel *channel)
                return 0;
 
        cur = ring->cur;
+
+       /* Be sure we get ring->cur before accessing descriptor data */
+       smp_rmb();
+
        txq = netdev_get_tx_queue(netdev, channel->queue_index);
 
        while ((processed < XGBE_TX_DESC_MAX_PROC) &&