netdev - Re: [PATCH net-next v4 7/7] net: devmem: allow binding on rx queues with same DMA devices

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Message-ID: <CAHS8izOQ=G-wVo5UXPyof+U=sxB-27Rv8UBfnVkvgtoOTW7Cdw@mail.gmail.com>
Date: Wed, 20 Aug 2025 15:57:32 -0700
From: Mina Almasry <almasrymina@...gle.com>
To: Dragos Tatulea <dtatulea@...dia.com>
Cc: asml.silence@...il.com, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Simon Horman <horms@...nel.org>, cratiu@...dia.com, parav@...dia.com, 
	netdev@...r.kernel.org, sdf@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v4 7/7] net: devmem: allow binding on rx queues
 with same DMA devices

On Wed, Aug 20, 2025 at 10:14 AM Dragos Tatulea <dtatulea@...dia.com> wrote:
>
> Multi-PF netdevs have queues belonging to different PFs which also means
> different DMA devices. This means that the binding on the DMA buffer can
> be done to the incorrect device.
>
> This change allows devmem binding to multiple queues only when the
> queues have the same DMA device. Otherwise an error is returned.
>
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> ---
>  net/core/netdev-genl.c | 34 +++++++++++++++++++++++++++++++++-
>  1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index 0df9c159e515..a8c27f636453 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -906,6 +906,33 @@ static int netdev_nl_read_rxq_bitmap(struct genl_info *info,
>         return 0;
>  }
>
> +static struct device *netdev_nl_get_dma_dev(struct net_device *netdev,
> +                                           unsigned long *rxq_bitmap,
> +                                           struct netlink_ext_ack *extack)
> +{
> +       struct device *dma_dev = NULL;
> +       u32 rxq_idx, prev_rxq_idx;
> +
> +       for_each_set_bit(rxq_idx, rxq_bitmap, netdev->real_num_rx_queues) {
> +               struct device *rxq_dma_dev;
> +
> +               rxq_dma_dev = netdev_queue_get_dma_dev(netdev, rxq_idx);
> +               /* Multi-PF netdev queues can belong to different DMA devoces.
> +                * Block this case.
> +                */
> +               if (dma_dev && rxq_dma_dev != dma_dev) {
> +                       NL_SET_ERR_MSG_FMT(extack, "Queue %u has a different dma device than queue %u",
> +                                          rxq_idx, prev_rxq_idx);
> +                       return ERR_PTR(-EOPNOTSUPP);
> +               }
> +
> +               dma_dev = rxq_dma_dev;
> +               prev_rxq_idx = rxq_idx;
> +       }
> +
> +       return dma_dev;
> +}
> +
>  int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>  {
>         struct net_devmem_dmabuf_binding *binding;
> @@ -969,7 +996,12 @@ int netdev_nl_bind_rx_doit(struct sk_buff *skb, struct genl_info *info)
>         if (err)
>                 goto err_rxq_bitmap;
>
> -       dma_dev = netdev_queue_get_dma_dev(netdev, 0);
> +       dma_dev = netdev_nl_get_dma_dev(netdev, rxq_bitmap, info->extack);
> +       if (IS_ERR(dma_dev)) {

Does this need to be IS_ERR_OR_NULL? AFAICT if all the ndos return
NULL, then dma_dev will also be NULL, and NULL is not a valid value to
pass to bind_dmabuf below.


-- 
Thanks,
Mina