Patch "net: ll_temac: Add memory-barriers for TX BD access" has been added to the 5.12-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    net: ll_temac: Add memory-barriers for TX BD access

to the 5.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-ll_temac-add-memory-barriers-for-tx-bd-access.patch
and it can be found in the queue-5.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 57b344acdcfbf41e4008672ebd00e340fc4c7582
Author: Esben Haabendal <esben@xxxxxxxxxx>
Date:   Fri Jun 18 12:52:28 2021 +0200

    net: ll_temac: Add memory-barriers for TX BD access
    
    [ Upstream commit 28d9fab458b16bcd83f9dd07ede3d585c3e1a69e ]
    
    Add a couple of memory-barriers to ensure correct ordering of read/write
    access to TX BDs.
    
    In xmit_done, we should ensure that reading the additional BD fields are
    only done after STS_CTRL_APP0_CMPLT bit is set.
    
    When xmit_done marks the BD as free by setting APP0=0, we need to ensure
    that the other BD fields are reset first, so we avoid racing with the xmit
    path, which writes to the same fields.
    
    Finally, making sure to read APP0 of next BD after the current BD, ensures
    that we see all available buffers.
    
    Signed-off-by: Esben Haabendal <esben@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/xilinx/ll_temac_main.c b/drivers/net/ethernet/xilinx/ll_temac_main.c
index 01bb36e7cff0..b105e1d35d15 100644
--- a/drivers/net/ethernet/xilinx/ll_temac_main.c
+++ b/drivers/net/ethernet/xilinx/ll_temac_main.c
@@ -774,12 +774,15 @@ static void temac_start_xmit_done(struct net_device *ndev)
 	stat = be32_to_cpu(cur_p->app0);
 
 	while (stat & STS_CTRL_APP0_CMPLT) {
+		/* Make sure that the other fields are read after bd is
+		 * released by dma
+		 */
+		rmb();
 		dma_unmap_single(ndev->dev.parent, be32_to_cpu(cur_p->phys),
 				 be32_to_cpu(cur_p->len), DMA_TO_DEVICE);
 		skb = (struct sk_buff *)ptr_from_txbd(cur_p);
 		if (skb)
 			dev_consume_skb_irq(skb);
-		cur_p->app0 = 0;
 		cur_p->app1 = 0;
 		cur_p->app2 = 0;
 		cur_p->app3 = 0;
@@ -788,6 +791,12 @@ static void temac_start_xmit_done(struct net_device *ndev)
 		ndev->stats.tx_packets++;
 		ndev->stats.tx_bytes += be32_to_cpu(cur_p->len);
 
+		/* app0 must be visible last, as it is used to flag
+		 * availability of the bd
+		 */
+		smp_mb();
+		cur_p->app0 = 0;
+
 		lp->tx_bd_ci++;
 		if (lp->tx_bd_ci >= lp->tx_bd_num)
 			lp->tx_bd_ci = 0;
@@ -814,6 +823,9 @@ static inline int temac_check_tx_bd_space(struct temac_local *lp, int num_frag)
 		if (cur_p->app0)
 			return NETDEV_TX_BUSY;
 
+		/* Make sure to read next bd app0 after this one */
+		rmb();
+
 		tail++;
 		if (tail >= lp->tx_bd_num)
 			tail = 0;