On Mon, May 4, 2026 at 5:27 PM Bobby Eshleman <[email protected]> wrote: > > From: Bobby Eshleman <[email protected]> > > Devices that support netmem TX previously set dev->netmem_tx = true. > This was checked in validate_xmit_unreadable_skb() to drop unreadable > skbs (skbs with dmabuf-backed frags) before they reach drivers that > would mishandle them or devices that would not have the iommu mappings > for them. > > Some virtual devices like netkit (or ifb) never DMA and never touch frag > contents, as they essentially just forward the skb to another device. > They are unable to forward unreadable skbs, however, because they fail > to pass TX validation checks on dev->netmem_tx. This single bit flag > doesn't give the TX validator enough information to differentiate > devices that will attempt DMA on the unreadable skb and those that will > simply route it untouched. > > This patch fixes this issue by adding an additional bit to netmem_tx, so > that drivers can indicate 1) if they have netmem support, and 2) if they > do, are they DMA-capable or not? > > Replace the boolean with a 2-bit enum: > > NETMEM_TX_NONE - no netmem TX support (drop unreadable skbs) > NETMEM_TX_DMA - full support, device does DMA > NETMEM_TX_NO_DMA - pass-through, device never DMAs > > Update drivers to reflect these definitions. NIC drivers use > NETMEM_TX_DMA, and netkit uses NETMEM_TX_NO_DMA. > > Signed-off-by: Bobby Eshleman <[email protected]> > --- > Changes in v2: > - Squash driver conversion patches (2-5) into patch 1 (Jakub) > --- > Documentation/networking/net_cachelines/net_device.rst | 2 +- > Documentation/networking/netmem.rst | 8 +++++++- > Documentation/translations/zh_CN/networking/netmem.rst | 7 ++++++- > drivers/net/ethernet/broadcom/bnxt/bnxt.c | 2 +- > drivers/net/ethernet/google/gve/gve_main.c | 2 +- > drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 2 +- > drivers/net/ethernet/meta/fbnic/fbnic_netdev.c | 2 +- > drivers/net/netkit.c | 1 + > include/linux/netdevice.h | 11 +++++++++-- > 9 files changed, 28 insertions(+), 9 deletions(-) > > diff --git a/Documentation/networking/net_cachelines/net_device.rst > b/Documentation/networking/net_cachelines/net_device.rst > index 1c19bb7705df..c85784259544 100644 > --- a/Documentation/networking/net_cachelines/net_device.rst > +++ b/Documentation/networking/net_cachelines/net_device.rst > @@ -10,7 +10,7 @@ Type Name > fastpath_tx_acce > =================================== =========================== > =================== =================== > =================================================================================== > unsigned_long:32 priv_flags read_mostly > __dev_queue_xmit(tx) > unsigned_long:1 lltx read_mostly > HARD_TX_LOCK,HARD_TX_TRYLOCK,HARD_TX_UNLOCK(tx) > -unsigned long:1 netmem_tx:1; read_mostly > +unsigned long:2 netmem_tx:2; read_mostly > char name[16] > struct netdev_name_node* name_node > struct dev_ifalias* ifalias > diff --git a/Documentation/networking/netmem.rst > b/Documentation/networking/netmem.rst > index b63aded46337..217869d1108d 100644 > --- a/Documentation/networking/netmem.rst > +++ b/Documentation/networking/netmem.rst > @@ -95,4 +95,10 @@ Driver TX Requirements > netdev@, or reach out to the maintainers and/or [email protected] for > help adding the netmem API. > > -2. Driver should declare support by setting `netdev->netmem_tx = true` > +2. Driver should declare support by setting `netdev->netmem_tx` to the > + appropriate mode: > + > + - `NETMEM_TX_DMA`: for physical devices that perform DMA. > + > + - `NETMEM_TX_NO_DMA`: for virtual or passthrough devices that do > + not DMA, but still support handling of netmem-backed skbs. > diff --git a/Documentation/translations/zh_CN/networking/netmem.rst > b/Documentation/translations/zh_CN/networking/netmem.rst > index fe351a240f02..320f3eacf51b 100644 > --- a/Documentation/translations/zh_CN/networking/netmem.rst > +++ b/Documentation/translations/zh_CN/networking/netmem.rst > @@ -89,4 +89,9 @@ dma-mapping API 去处理。 > 使用某个还不存在的 netmem API，你可以自行添加并提交到 netdev@，也可以联系维护 > 人员或者发送邮件至 [email protected] 寻求帮助。 > > -2. 驱动程序应通过设置 netdev->netmem_tx = true 来表明自身支持 netmem 功能。 > +2. 驱动程序应将 `netdev->netmem_tx` 设置为适当的模式： > + > + - `NETMEM_TX_DMA`：适用于执行 DMA 的物理设备。 > + > + - `NETMEM_TX_NO_DMA`：适用于不执行 DMA 的虚拟或透传设备，但仍支持 > + 处理 netmem 支持的 skb。 > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c > b/drivers/net/ethernet/broadcom/bnxt/bnxt.c > index 8c55874f44ca..ed9c22dc4a5a 100644 > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c > @@ -17120,7 +17120,7 @@ static int bnxt_init_one(struct pci_dev *pdev, const > struct pci_device_id *ent) > dev->queue_mgmt_ops = &bnxt_queue_mgmt_ops_unsupp; > if (BNXT_SUPPORTS_QUEUE_API(bp)) > dev->queue_mgmt_ops = &bnxt_queue_mgmt_ops; > - dev->netmem_tx = true; > + dev->netmem_tx = NETMEM_TX_DMA; > > rc = register_netdev(dev); > if (rc) > diff --git a/drivers/net/ethernet/google/gve/gve_main.c > b/drivers/net/ethernet/google/gve/gve_main.c > index 424d973c97f2..dd2b8f087163 100644 > --- a/drivers/net/ethernet/google/gve/gve_main.c > +++ b/drivers/net/ethernet/google/gve/gve_main.c > @@ -2894,7 +2894,7 @@ static int gve_probe(struct pci_dev *pdev, const struct > pci_device_id *ent) > goto abort_with_wq; > > if (!gve_is_gqi(priv) && !gve_is_qpl(priv)) > - dev->netmem_tx = true; > + dev->netmem_tx = NETMEM_TX_DMA;
Acked-by: Harshitha Ramamurthy <[email protected]> > > err = register_netdev(dev); > if (err) > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > index 5a46870c4b74..fc49aae38807 100644 > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c > @@ -5924,7 +5924,7 @@ static void mlx5e_build_nic_netdev(struct net_device > *netdev) > > netdev->priv_flags |= IFF_UNICAST_FLT; > > - netdev->netmem_tx = true; > + netdev->netmem_tx = NETMEM_TX_DMA; > > netif_set_tso_max_size(netdev, GSO_MAX_SIZE); > mlx5e_set_xdp_feature(priv); > diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_netdev.c > b/drivers/net/ethernet/meta/fbnic/fbnic_netdev.c > index c406a3b56b37..138e522ef9b9 100644 > --- a/drivers/net/ethernet/meta/fbnic/fbnic_netdev.c > +++ b/drivers/net/ethernet/meta/fbnic/fbnic_netdev.c > @@ -752,7 +752,7 @@ struct net_device *fbnic_netdev_alloc(struct fbnic_dev > *fbd) > netdev->netdev_ops = &fbnic_netdev_ops; > netdev->stat_ops = &fbnic_stat_ops; > netdev->queue_mgmt_ops = &fbnic_queue_mgmt_ops; > - netdev->netmem_tx = true; > + netdev->netmem_tx = NETMEM_TX_DMA; > > fbnic_set_ethtool_ops(netdev); > > diff --git a/drivers/net/netkit.c b/drivers/net/netkit.c > index 5e2eecc3165d..0ad6a806d7d5 100644 > --- a/drivers/net/netkit.c > +++ b/drivers/net/netkit.c > @@ -466,6 +466,7 @@ static void netkit_setup(struct net_device *dev) > dev->priv_flags |= IFF_NO_QUEUE; > dev->priv_flags |= IFF_DISABLE_NETPOLL; > dev->lltx = true; > + dev->netmem_tx = NETMEM_TX_NO_DMA; > > dev->netdev_ops = &netkit_netdev_ops; > dev->ethtool_ops = &netkit_ethtool_ops; > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h > index 0e1e581efc5a..11d68e75eb4f 100644 > --- a/include/linux/netdevice.h > +++ b/include/linux/netdevice.h > @@ -1788,6 +1788,12 @@ enum netdev_stat_type { > NETDEV_PCPU_STAT_DSTATS, /* struct pcpu_dstats */ > }; > > +enum netmem_tx_mode { > + NETMEM_TX_NONE, /* no netmem TX support */ > + NETMEM_TX_DMA, /* DMA-capable netmem TX (real HW) */ > + NETMEM_TX_NO_DMA, /* no DMA, e.g. passthrough for virtual devs > */ > +}; > + > enum netdev_reg_state { > NETREG_UNINITIALIZED = 0, > NETREG_REGISTERED, /* completed register_netdevice */ > @@ -1809,7 +1815,8 @@ enum netdev_reg_state { > * @lltx: device supports lockless Tx. Deprecated for real HW > * drivers. Mainly used by logical interfaces, such as > * bonding and tunnels > - * @netmem_tx: device support netmem_tx. > + * @netmem_tx: device netmem TX mode (NETMEM_TX_NONE, NETMEM_TX_DMA, > + * or NETMEM_TX_NO_DMA). > * > * @name: This is the first field of the "visible" part of this > structure > * (i.e. as seen by users in the "Space.c" file). It is the name > @@ -2132,7 +2139,7 @@ struct net_device { > struct_group(priv_flags_fast, > unsigned long priv_flags:32; > unsigned long lltx:1; > - unsigned long netmem_tx:1; > + unsigned long netmem_tx:2; > ); > const struct net_device_ops *netdev_ops; > const struct header_ops *header_ops; > > -- > 2.52.0 >
