On 02/21, Mina Almasry wrote:
> On Thu, Feb 20, 2025 at 11:13 AM Stanislav Fomichev
> <stfomichev@xxxxxxxxx> wrote:
> >
> > On 02/20, Mina Almasry wrote:
> > > 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@xxxxxxxxxx>
> > >
> > > ---
> > >
> > > v4:
> > > - New patch
> > > ---
> > > .../networking/net_cachelines/net_device.rst | 1 +
> > > Documentation/networking/netdev-features.rst | 5 +++++
> > > Documentation/networking/netmem.rst | 14 +++++++++++--
> > > include/linux/netdevice.h | 2 ++
> > > include/net/netmem.h | 20 +++++++++++++++++++
> > > 5 files changed, 40 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/Documentation/networking/net_cachelines/net_device.rst b/Documentation/networking/net_cachelines/net_device.rst
> > > index 15e31ece675f..e3043b033647 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 5014f7cc1398..02bd7536fc0c 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 7de21ddb5412..43054d44c407 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 +77,13 @@ 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. Driver should use netmem_dma_unmap_page_attrs() in lieu of
> > > + dma_unmap_page[_attrs](), and netmem_dma_unmap_addr_set() in lieu of
> > > + dma_unmap_addr_set(). The netmem variants will handle netmems that should
> > > + not be dma-unmapped by the driver, such as dma-buf netmems.
> >
> > Not all drivers use dma_unmap_addr_xxx APIs (looking at mlx5). Might
> > be worth mentioning that for the drivers managing the mappings
> > differently, care might be taken to not unmap netmems?
> >
>
> Yes now that I take a closer look, it's poorly worded to imply the
> issue is limited to dma_unmap. I will reword to say that all
> dma_map*() APIs must be avoided, and we have helpers for
> dma_unmap_*(), and more helpers can be added if needed (similar to
> wording in the Driver RX requirements).
>
> > > +2. Driver should declare support by setting `netdev->netmem_tx = true`
> > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > index fccc03cd2164..d8cfd5d69ddf 100644
> > > --- a/include/linux/netdevice.h
> > > +++ b/include/linux/netdevice.h
> > > @@ -1753,6 +1753,7 @@ 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
> > > @@ -2061,6 +2062,7 @@ 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 a2148ffb203d..1fb39ad63290 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>
> > >
> > > @@ -267,4 +268,23 @@ 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)
> >
> > Any reason not do to static inline instaed?
>
> Because the args passed to dma_unmap_addr_set are quite unique,
> AFAICT. PTR is a pointer to any struct that has a field (anywhere)
> inside of it called ADDR_NAME, then dma_unmap_addr_set does something
> like:
>
> PTR->ADDR_NAME = VAL;
>
> A static inline needs well defined types, and I couldn't figure out
> how to do that (or if it is possible), so a macro it is I guess.
>
> Where I could, I went with static inline.
Ah dma_unmap_addr_set itself is an ugly define :-( Makes sense.
