[PATCH net-next v7 8/9] net: check for driver support in netmem TX

[Mina Almasry <almasrymina@google.com>]

We should not enable netmem TX for drivers that don't declare support.

Check for driver netmem TX support during devmem TX binding and fail if
the driver does not have the functionality.

Check for driver support in validate_xmit_skb as well.

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

---

v5: https://lore.kernel.org/netdev/20250227041209.2031104-8-almasrymina@google.com/
- Check that the dmabuf mappings belongs to the specific device the TX
  is being sent from (Jakub)

v4:
- New patch

---
 net/core/dev.c         | 33 +++++++++++++++++++++++++++++++++
 net/core/devmem.h      |  6 ++++++
 net/core/netdev-genl.c |  7 +++++++
 3 files changed, 46 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 1cb134ff7327..5553947123a0 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3868,10 +3868,43 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
 }
 EXPORT_SYMBOL(skb_csum_hwoffload_help);
 
+static struct sk_buff *validate_xmit_unreadable_skb(struct sk_buff *skb,
+						    struct net_device *dev)
+{
+	struct skb_shared_info *shinfo;
+	struct net_iov *niov;
+
+	if (likely(skb_frags_readable(skb)))
+		goto out;
+
+	if (likely(!dev->netmem_tx))
+		goto out_free;
+
+	shinfo = skb_shinfo(skb);
+
+	if (shinfo->nr_frags > 0) {
+		niov = netmem_to_net_iov(skb_frag_netmem(&shinfo->frags[0]));
+		if (net_is_devmem_iov(niov) &&
+		    net_devmem_iov_binding(niov)->dev != dev)
+			goto out_free;
+	}
+
+out:
+	return skb;
+
+out_free:
+	kfree_skb(skb);
+	return NULL;
+}
+
 static struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device *dev, bool *again)
 {
 	netdev_features_t features;
 
+	skb = validate_xmit_unreadable_skb(skb, dev);
+	if (unlikely(!skb))
+		goto out_null;
+
 	features = netif_skb_features(skb);
 	skb = validate_xmit_vlan(skb, features);
 	if (unlikely(!skb))
diff --git a/net/core/devmem.h b/net/core/devmem.h
index 67168aae5e5b..919e6ed28fdc 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -229,6 +229,12 @@ net_devmem_get_niov_at(struct net_devmem_dmabuf_binding *binding, size_t addr,
 {
 	return NULL;
 }
+
+static inline struct net_devmem_dmabuf_binding *
+net_devmem_iov_binding(const struct net_iov *niov)
+{
+	return NULL;
+}
 #endif
 
 #endif /* _NET_DEVMEM_H */
diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
index 6e7cd6a5c177..6c5d62df0d65 100644
--- a/net/core/netdev-genl.c
+++ b/net/core/netdev-genl.c
@@ -972,6 +972,13 @@ int netdev_nl_bind_tx_doit(struct sk_buff *skb, struct genl_info *info)
 		goto err_unlock;
 	}
 
+	if (!netdev->netmem_tx) {
+		err = -EOPNOTSUPP;
+		NL_SET_ERR_MSG(info->extack,
+			       "Driver does not support netmem TX");
+		goto err_unlock;
+	}
+
 	binding = net_devmem_bind_dmabuf(netdev, DMA_TO_DEVICE, dmabuf_fd,
 					 info->extack);
 	if (IS_ERR(binding)) {
-- 
2.49.0.rc0.332.g42c0ae87b1-goog