Re: [PATCH net] net: sgi: ioc3-eth: fix split TX DMA mapping lengths

[Thomas Bogendoerfer <tsbogend@alpha.franken.de>]

On Mon, Jun 29, 2026 at 04:06:23PM +0800, raoxu wrote:
> From: Xu Rao <raoxu@uniontech.com>
> 
> When a linear skb crosses a 16 KiB boundary, ioc3_start_xmit()
> splits it into two buffers of lengths s1 and s2.  The descriptor
> advertises those lengths through B1CNT and B2CNT.
> 
> The first buffer is mapped with s1, but the second buffer is also
> mapped with s1 even though the device is told to fetch s2 bytes from
> it.  When the lengths differ, the DMA mapping does not cover the same
> region as the second descriptor buffer, which can result in incorrect
> cache maintenance or a DMA fault on implementations that enforce the
> mapped range.
> 
> There is a separate mismatch in the error path.  If mapping the second
> buffer fails, only d1 needs to be unmapped.  d1 was mapped for s1 bytes,
> but the driver unmaps it using the full packet length.  Streaming DMA
> mappings must be unmapped with the same size used for the corresponding
> map operation.
> 
> Map the second buffer with s2 and unmap the first buffer with s1 when
> the second mapping fails.
> 
> Fixes: ed870f6a7aa2 ("net: sgi: ioc3-eth: use dma-direct for dma allocations")
> Cc: stable@vger.kernel.org
> Signed-off-by: Xu Rao <raoxu@uniontech.com>
> ---
>  drivers/net/ethernet/sgi/ioc3-eth.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/sgi/ioc3-eth.c b/drivers/net/ethernet/sgi/ioc3-eth.c
> index 3973106..261f2d3 100644
> --- a/drivers/net/ethernet/sgi/ioc3-eth.c
> +++ b/drivers/net/ethernet/sgi/ioc3-eth.c
> @@ -1061,9 +1061,9 @@ static netdev_tx_t ioc3_start_xmit(struct sk_buff *skb, struct net_device *dev)
>  		d1 = dma_map_single(ip->dma_dev, skb->data, s1, DMA_TO_DEVICE);
>  		if (dma_mapping_error(ip->dma_dev, d1))
>  			goto drop_packet;
> -		d2 = dma_map_single(ip->dma_dev, (void *)b2, s1, DMA_TO_DEVICE);
> +		d2 = dma_map_single(ip->dma_dev, (void *)b2, s2, DMA_TO_DEVICE);
>  		if (dma_mapping_error(ip->dma_dev, d2)) {
> -			dma_unmap_single(ip->dma_dev, d1, len, DMA_TO_DEVICE);
> +			dma_unmap_single(ip->dma_dev, d1, s1, DMA_TO_DEVICE);
>  			goto drop_packet;
>  		}
>  		desc->p1     = cpu_to_be64(ioc3_map(d1, PCI64_ATTR_PREF));
> -- 
> 2.47.3

Reviewed-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

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