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, guaranteeing 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. --- Changes in v4: - remove enum list from netmem_tx comment (Stan) - fold NETMEM_TX_NO_DMA check in validate_xmit_unreadable_skb() into skb_frags_readable check (Stan, Jakub) - change binding->vdev to void ptr cookie with comment (Jakub) - Fixed the bad change list version number (Stan) - Link to v3: https://lore.kernel.org/r/[email protected] Changes in v3: - Fix validate_xmit_unreadable_skb() logic for non-devmem unreadable niovs (should not be dropped) (Sashiko) - Simplify lock handling in bind_tx, no premature release (Jakub) - split NO_DMA changes into separate patch (Jakub) - fixed some pylint issues, one required an additional patch ("selftests: drv-net: make attr _nk_guest_ifname public") to rename a variable from private to public - see per-patch changelist for more detailed changes - Link to v2: https://lore.kernel.org/r/[email protected] Changes in v2: - Squash driver conversion patches (2-5) into patch 1 (Jakub) - In validate_xmit_unreadable_skb() to check netmem_tx mode before inspecting frags (Jakub) - Lock bind_dev around netdev_queue_get_dma_dev() when bind_dev != netdev to fix lockdep (Sashiko) - Move require_devmem() into individual test functions so KsftSkipEx goes up to ksft_run() (Sashiko) - Add nk_devmem.py to TEST_PROGS in Makefile (Sashiko) - Link to v1: https://lore.kernel.org/all/[email protected]/ Signed-off-by: Bobby Eshleman <[email protected]> --- Bobby Eshleman (8): net: convert netmem_tx flag to enum net: netkit: declare NETMEM_TX_NO_DMA mode net: devmem: support TX over NETMEM_TX_NO_DMA devices selftests: drv-net: ncdevmem: add -n flag to skip NIC configuration selftests: drv-net: make attr _nk_guest_ifname public 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 | 10 +- net/core/dev.c | 5 +- net/core/devmem.c | 6 +- net/core/devmem.h | 10 +- net/core/netdev-genl.c | 65 +++++- tools/testing/selftests/drivers/net/hw/Makefile | 1 + tools/testing/selftests/drivers/net/hw/devmem.py | 77 ++------ .../selftests/drivers/net/hw/lib/py/devmem.py | 218 +++++++++++++++++++++ tools/testing/selftests/drivers/net/hw/ncdevmem.c | 58 +++--- .../testing/selftests/drivers/net/hw/nk_devmem.py | 55 ++++++ .../drivers/net/hw/nk_primary_rx_redirect.bpf.c | 39 ++++ .../testing/selftests/drivers/net/hw/nk_qlease.py | 8 +- tools/testing/selftests/drivers/net/lib/py/env.py | 109 ++++++++--- 21 files changed, 548 insertions(+), 139 deletions(-) --- base-commit: 790ead9394860e7d70c5e0e50a35b243e909a618 change-id: 20260423-tcp-dm-netkit-2bd78b638d30 Best regards, -- Bobby Eshleman <[email protected]>
