platform/mellanox: mlxbf-tmfifo: Fix a memory barrier issue

The virtio framework uses wmb() when updating avail->idx. It
guarantees the write order, but not necessarily loading order
for the code accessing the memory. This commit adds a load barrier
after reading the avail->idx to make sure all the data in the
descriptor is visible. It also adds a barrier when returning the
packet to virtio framework to make sure read/writes are visible to
the virtio code.

Fixes: 1357dfd7261f ("platform/mellanox: Add TmFifo driver for Mellanox BlueField Soc")
Signed-off-by: Liming Sun <limings@nvidia.com>
Reviewed-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/1620433812-17911-1-git-send-email-limings@nvidia.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/drivers/platform/mellanox/mlxbf-tmfifo.c b/drivers/platform/mellanox/mlxbf-tmfifo.c
index bbc4e71..38800e8 100644 (file)
--- a/drivers/platform/mellanox/mlxbf-tmfifo.c
+++ b/drivers/platform/mellanox/mlxbf-tmfifo.c
@@ -294,6 +294,9 @@ mlxbf_tmfifo_get_next_desc(struct mlxbf_tmfifo_vring *vring)
        if (vring->next_avail == virtio16_to_cpu(vdev, vr->avail->idx))
                return NULL;
 
+       /* Make sure 'avail->idx' is visible already. */
+       virtio_rmb(false);
+
        idx = vring->next_avail % vr->num;
        head = virtio16_to_cpu(vdev, vr->avail->ring[idx]);
        if (WARN_ON(head >= vr->num))
@@ -322,7 +325,7 @@ static void mlxbf_tmfifo_release_desc(struct mlxbf_tmfifo_vring *vring,
         * done or not. Add a memory barrier here to make sure the update above
         * completes before updating the idx.
         */
-       mb();
+       virtio_mb(false);
        vr->used->idx = cpu_to_virtio16(vdev, vr_idx + 1);
 }
 
@@ -733,6 +736,12 @@ static bool mlxbf_tmfifo_rxtx_one_desc(struct mlxbf_tmfifo_vring *vring,
                desc = NULL;
                fifo->vring[is_rx] = NULL;
 
+               /*
+                * Make sure the load/store are in order before
+                * returning back to virtio.
+                */
+               virtio_mb(false);
+
                /* Notify upper layer that packet is done. */
                spin_lock_irqsave(&fifo->spin_lock[is_rx], flags);
                vring_interrupt(0, vring->vq);