On Tue, Aug 6, 2019 at 2:38 AM Firo Yang <firo.y...@suse.com> wrote:
>
> In Xen environment, if Xen-swiotlb is enabled, ixgbe driver
> could possibly allocate a page, DMA memory buffer, for the first
> fragment which is not suitable for Xen-swiotlb to do DMA operations.
> Xen-swiotlb will internally allocate another page for doing DMA
> operations. It requires syncing between those two pages. Otherwise,
> we may get an incomplete skb. To fix this problem, sync the first
> fragment no matter the first fargment is makred as "page_released"
> or not.
>
> Signed-off-by: Firo Yang <firo.y...@suse.com>
>From what I can tell the code below is fine. However the patch
description isn't very clear about the issue.
Specifically since we are mapping the frame with
DMA_ATTR_SKIP_CPU_SYNC we have to unmap with that as well. As a result
a sync is not performed on an unmap and must be done manually as we
skipped it for the first frag. As such we need to always sync before
possibly performing a page unmap operation.
Also you can probably add the following to your patch description"
Fixes: f3213d932173 ("ixgbe: Update driver to make use of DMA
attributes in Rx path")
Reviewed-by: Alexander Duyck <alexander.h.du...@linux.intel.com>
> ---
> drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index cbaf712d6529..200de9838096 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -1825,13 +1825,7 @@ static void ixgbe_pull_tail(struct ixgbe_ring *rx_ring,
> static void ixgbe_dma_sync_frag(struct ixgbe_ring *rx_ring,
> struct sk_buff *skb)
> {
> - /* if the page was released unmap it, else just sync our portion */
> - if (unlikely(IXGBE_CB(skb)->page_released)) {
> - dma_unmap_page_attrs(rx_ring->dev, IXGBE_CB(skb)->dma,
> - ixgbe_rx_pg_size(rx_ring),
> - DMA_FROM_DEVICE,
> - IXGBE_RX_DMA_ATTR);
> - } else if (ring_uses_build_skb(rx_ring)) {
> + if (ring_uses_build_skb(rx_ring)) {
> unsigned long offset = (unsigned long)(skb->data) &
> ~PAGE_MASK;
>
> dma_sync_single_range_for_cpu(rx_ring->dev,
> @@ -1848,6 +1842,14 @@ static void ixgbe_dma_sync_frag(struct ixgbe_ring
> *rx_ring,
> skb_frag_size(frag),
> DMA_FROM_DEVICE);
> }
> +
> + /* If the page was released, just unmap it. */
> + if (unlikely(IXGBE_CB(skb)->page_released)) {
> + dma_unmap_page_attrs(rx_ring->dev, IXGBE_CB(skb)->dma,
> + ixgbe_rx_pg_size(rx_ring),
> + DMA_FROM_DEVICE,
> + IXGBE_RX_DMA_ATTR);
> + }
> }
>
> /**
> --
> 2.16.4
>
