[PATCH net-next v13 6/9] net: enable driver support for netmem TX

Mina Almasry
2025-04-29T03:26:59Z

Drivers need to make sure not to pass netmem dma-addrs to the
dma-mapping API in order to support netmem TX.

Add helpers and netmem_dma_*() helpers that enables special handling of
netmem dma-addrs that drivers can use.

Document in netmem.rst what drivers need to do to support netmem TX.

Signed-off-by: Mina Almasry <almasrymina@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>

---

v8:
- use spaces instead of tabs (Paolo)

v5:
- Fix netmet TX documentation (Stan).

v4:
- New patch
---
.../networking/net_cachelines/net_device.rst | 1 +
Documentation/networking/netdev-features.rst | 5 ++++
Documentation/networking/netmem.rst | 23 +++++++++++++++++--
include/linux/netdevice.h | 2 ++
include/net/netmem.h | 20 ++++++++++++++++
5 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
index ca8605eb82ffc..c69cc89c958e0 100644
--- a/Documentation/networking/net_cachelines/net_device.rst
+++ b/Documentation/networking/net_cachelines/net_device.rst
@@ -10,6 +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
char name[16]
struct netdev_name_node* name_node
struct dev_ifalias* ifalias
diff --git a/Documentation/networking/netdev-features.rst b/Documentation/networking/netdev-features.rst
index 5014f7cc1398b..02bd7536fc0ca 100644
--- a/Documentation/networking/netdev-features.rst
+++ b/Documentation/networking/netdev-features.rst
@@ -188,3 +188,8 @@ Redundancy) frames from one port to another in hardware.
This should be set for devices which duplicate outgoing HSR (High-availability
Seamless Redundancy) or PRP (Parallel Redundancy Protocol) tags automatically
frames in hardware.
+
+* netmem-tx
+
+This should be set for devices which support netmem TX. See
+Documentation/networking/netmem.rst
diff --git a/Documentation/networking/netmem.rst b/Documentation/networking/netmem.rst
index 7de21ddb54129..b63aded463370 100644
--- a/Documentation/networking/netmem.rst
+++ b/Documentation/networking/netmem.rst
@@ -19,8 +19,8 @@ Benefits of Netmem :
* Simplified Development: Drivers interact with a consistent API,
regardless of the underlying memory implementation.

-Driver Requirements
-===================
+Driver RX Requirements
+======================

1. The driver must support page_pool.

@@ -77,3 +77,22 @@ Driver Requirements
that purpose, but be mindful that some netmem types might have longer
circulation times, such as when userspace holds a reference in zerocopy
scenarios.
+
+Driver TX Requirements
+======================
+
+1. The Driver must not pass the netmem dma_addr to any of the dma-mapping APIs
+ directly. This is because netmem dma_addrs may come from a source like
+ dma-buf that is not compatible with the dma-mapping APIs.
+
+ Helpers like netmem_dma_unmap_page_attrs() & netmem_dma_unmap_addr_set()
+ should be used in lieu of dma_unmap_page[_attrs](), dma_unmap_addr_set().
+ The netmem variants will handle netmem dma_addrs correctly regardless of the
+ source, delegating to the dma-mapping APIs when appropriate.
+
+ Not all dma-mapping APIs have netmem equivalents at the moment. If your
+ driver relies on a missing netmem API, feel free to add and propose to
+ netdev@, or reach out to the maintainers and/or almasrymina@google.com for
+ help adding the netmem API.
+
+2. Driver should declare support by setting `netdev->netmem_tx = true`
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 0321fd952f708..a661820a26c44 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1772,6 +1772,7 @@ 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.
*
* @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
@@ -2087,6 +2088,7 @@ struct net_device {
struct_group(priv_flags_fast,
unsigned long priv_flags:32;
unsigned long lltx:1;
+ unsigned long netmem_tx:1;
);
const struct net_device_ops *netdev_ops;
const struct header_ops *header_ops;
diff --git a/include/net/netmem.h b/include/net/netmem.h
index ecb6b29c93f61..386164fb9c185 100644
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -8,6 +8,7 @@
#ifndef _NET_NETMEM_H
#define _NET_NETMEM_H

+#include <linux/dma-mapping.h>
#include <linux/mm.h>
#include <net/net_debug.h>

@@ -276,4 +277,23 @@ static inline unsigned long netmem_get_dma_addr(netmem_ref netmem)
void get_netmem(netmem_ref netmem);
void put_netmem(netmem_ref netmem);

+#define netmem_dma_unmap_addr_set(NETMEM, PTR, ADDR_NAME, VAL) \
+ do { \
+ if (!netmem_is_net_iov(NETMEM)) \
+ dma_unmap_addr_set(PTR, ADDR_NAME, VAL); \
+ else \
+ dma_unmap_addr_set(PTR, ADDR_NAME, 0); \
+ } while (0)
+
+static inline void netmem_dma_unmap_page_attrs(struct device *dev,
+ dma_addr_t addr, size_t size,
+ enum dma_data_direction dir,
+ unsigned long attrs)
+{
+ if (!addr)
+ return;
+
+ dma_unmap_page_attrs(dev, addr, size, dir, attrs);
+}
+
#endif /* _NET_NETMEM_H */
--
2.49.0.901.g37484f566f-goog