sfc: Properly sync RX DMA buffer when it is not the last in the page

We may currently allocate two RX DMA buffers to a page, and only unmap
the page when the second is completed.  We do not sync the first RX
buffer to be completed; this can result in packet loss or corruption
if the last RX buffer completed in a NAPI poll is the first in a page
and is not DMA-coherent.  (In the middle of a NAPI poll, we will
handle the following RX completion and unmap the page *before* looking
at the content of the first buffer.)

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 10 insertions, 5 deletions

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index d780a0d096b..a5754916478 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -236,7 +236,8 @@ static int efx_init_rx_buffers_page(struct efx_rx_queue *rx_queue)
 }
 
 static void efx_unmap_rx_buffer(struct efx_nic *efx,
-                                struct efx_rx_buffer *rx_buf)
+                                struct efx_rx_buffer *rx_buf,
+                                unsigned int used_len)
 {
         if ((rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.page) {
                 struct efx_rx_page_state *state;
@@ -247,6 +248,10 @@ static void efx_unmap_rx_buffer(struct efx_nic *efx,
                                        state->dma_addr,
                                        efx_rx_buf_size(efx),
                                        DMA_FROM_DEVICE);
+                } else if (used_len) {
+                        dma_sync_single_for_cpu(&efx->pci_dev->dev,
+                                                rx_buf->dma_addr, used_len,
+                                                DMA_FROM_DEVICE);
                 }
         } else if (!(rx_buf->flags & EFX_RX_BUF_PAGE) && rx_buf->u.skb) {
                 dma_unmap_single(&efx->pci_dev->dev, rx_buf->dma_addr,
@@ -269,7 +274,7 @@ static void efx_free_rx_buffer(struct efx_nic *efx,
 static void efx_fini_rx_buffer(struct efx_rx_queue *rx_queue,
                                struct efx_rx_buffer *rx_buf)
 {
-        efx_unmap_rx_buffer(rx_queue->efx, rx_buf);
+        efx_unmap_rx_buffer(rx_queue->efx, rx_buf, 0);
         efx_free_rx_buffer(rx_queue->efx, rx_buf);
 }
 
@@ -535,10 +540,10 @@ void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,
                 goto out;
         }
 
-        /* Release card resources - assumes all RX buffers consumed in-order
-         * per RX queue
+        /* Release and/or sync DMA mapping - assumes all RX buffers
+         * consumed in-order per RX queue
          */
-        efx_unmap_rx_buffer(efx, rx_buf);
+        efx_unmap_rx_buffer(efx, rx_buf, len);
 
         /* Prefetch nice and early so data will (hopefully) be in cache by
          * the time we look at it.