This series enables TCP devmem TX through netkit devices. Netkit now supports queue leasing. A physical NIC's RX queue can be leased to a netkit guest interface inside a container namespace. This gives the container a devmem-capable data path on the RX side (bind-rx, etc...). On the TX side, the container process binds to its netkit guest interface and sends traffic that netkit redirects (via BPF or ip forwarding) to the physical NIC for DMA.
Two things in the existing devmem TX path prevent this from working: 1. validate_xmit_unreadable_skb() requires dev->netmem_tx before it will forward a dmabuf-backed (unreadable) skb. This protects skbs from landing on devices that don't have the IOMMU mappings for the backing dmabuf or that don't speak netmem. Netkit, however, does not support DMA, doesn't attempt to read unreadable skb pages and so doesn't break netmem (it is pure skb routing and redirection). It is functionally capable of routing unreadable skbs, but there is no way for the TX validation pathway to distinguish between a device that will actually attempt DMA-ing the skb and another device (like netkit) that does not DMA but also does not break netmem. 2. bind_tx_doit uses the bound device as the DMA device. When the user binds devmem TX to the netkit guest, the bind handler attempts to create DMA mappings against netkit, which has no DMA capability and no IOMMU mappings. This series solves these problems as follows: 1. Extend netmem_tx to two bits, assigned to one of three values: NETMEM_TX_NONE - netmem not supported NETMEM_TX_DMA - netmem supported and performs DMA NETMEM_TX_NO_DMA - netmem supported, but does not DMA With these bits, phys devices can set NETMEM_TX_DMA and devices like netkit set NETMEM_TX_NO_DMA. The validation TX path ensures that any DMA-capable netdev exactly matches the bound device, guarantee the correct mapping of the bound dmabuf. The validation TX path also allows devices with NETMEM_TX_NO_DMA to pass, knowing these devices will not misuse netmem or run into IOMMU faults. After redirection or routing and the skb finally makes its way through the stack to a physical device's TX path, the above NETMEM_TX_DMA check is performed again to guarantee the device has the appropriate binding/mappings. 2. On TX bind, the bind handler recognizes NETMEM_TX_NO_DMA devices and finds the phys TX device and binds to that instead. For the netkit case, if it has been leased a queue from a DMA-capable device already, then the bind action is performed on the DMA-capable device instead and the dmabuf is mapped correctly. Signed-off-by: Bobby Eshleman <[email protected]> --- Bobby Eshleman (11): net: add netmem_tx modes that indicate dma capability net: bnxt: convert netmem_tx from bool to NETMEM_TX_DMA enum gve: convert netmem_tx from bool to NETMEM_TX_DMA enum net/mlx5e: convert netmem_tx from bool to NETMEM_TX_DMA enum eth: fbnic: convert netmem_tx from bool to NETMEM_TX_DMA enum netkit: set NETMEM_TX_NO_DMA for unreadable skb passthrough net: devmem: support TX over NETMEM_TX_NO_DMA devices selftests: drv-net: ncdevmem: add -n flag to skip NIC configuration selftests: drv-net: refactor devmem command builders into lib module selftests: drv-net: add primary_rx_redirect support to NetDrvContEnv selftests: drv-net: add netkit devmem tests .../networking/net_cachelines/net_device.rst | 2 +- Documentation/networking/netmem.rst | 8 +- .../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 +- net/core/dev.c | 24 ++- net/core/devmem.c | 6 +- net/core/devmem.h | 9 +- net/core/netdev-genl.c | 53 ++++- tools/testing/selftests/drivers/net/hw/devmem.py | 73 +------ .../selftests/drivers/net/hw/lib/py/devmem.py | 215 +++++++++++++++++++++ tools/testing/selftests/drivers/net/hw/ncdevmem.c | 58 +++--- .../testing/selftests/drivers/net/hw/nk_devmem.py | 40 ++++ .../drivers/net/hw/nk_primary_rx_redirect.bpf.c | 41 ++++ tools/testing/selftests/drivers/net/lib/py/env.py | 67 +++++-- 19 files changed, 498 insertions(+), 125 deletions(-) --- base-commit: 790ead9394860e7d70c5e0e50a35b243e909a618 change-id: 20260423-tcp-dm-netkit-2bd78b638d30 Best regards, -- Bobby Eshleman <[email protected]>
