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 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 | 11 +-
net/core/dev.c | 5 +-
net/core/devmem.c | 6 +-
net/core/devmem.h | 9 +-
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, 549 insertions(+), 138 deletions(-)
---
base-commit: 790ead9394860e7d70c5e0e50a35b243e909a618
change-id: 20260423-tcp-dm-netkit-2bd78b638d30
Best regards,
--
Bobby Eshleman <[email protected]>
