Re: [PATCH net-next 00/10] net/mlx5e: Add netdev support for data direct

[Mina Almasry]

On Thu, Oct 8, 2026 at 6:28 AM Tariq Toukan <tariqt@xxxxxxxxxx> wrote:
>
> Hi,
>
> This patch series by Dragos adds data direct support for netdev devices,
> allowing a mlx5 netdev to issue DMA commands through multiple paths.
> This feature is critical for improving performance and reaching line
> rate in certain environments where issuing PCI transactions over one
> path may be significantly faster than over another. These differences
> can arise from various PCI generations in the system or the specific
> system topology.
>
> Data direct for netdev will work with devmem by returning the data
> direct DMA device instead of the DMA device of the NIC. Each PF netdev
> registers its own data direct device and support for RX and TX datapath
> is added. The feature is selected through a new data direct priv flag.
>
> The feature is enabled though a ethtool private flag. When this flag
> is enabled, the driver will return the data direct device in the
> ndo_queue_get_dma_dev op.
>
> During data_direct device unbind, a re-creation of the channels is
> triggered.
>
> A note about the unbind: it does not does not tear down dmabuf bindings
> attached to the data direct device; the recreated channels will still
> pick up the binding via rxq->mp_params and post DMA addresses from the
> data direct IOMMU domain to the PF, causing IOMMU faults. A devmem
> revoke hook is needed to close those bindings before the switch. This is
> out of scope for this series.
>

Elaborate on this please. Are you referring to the fact that on
page_pool_scrub we unmap the netmems dma-mapped by the page-pool, but
we don't unmap the netmems dma-mapped by the memory provider?

What's the impact of leaving this unfixed? Is the machine going to
crash if the device goes away but we don't unmap the dmabuf?
-- 
Thanks,
Mina