net: prepare for non devmem TCP memory providers

There is a good bunch of places in generic paths assuming that the only
page pool memory provider is devmem TCP. As we want to reuse the net_iov
and provider infrastructure, we need to patch it up and explicitly check
the provider type when we branch into devmem TCP code.

Reviewed-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Wei <dw@davidwei.uk>
Link: https://patch.msgid.link/20250204215622.695511-9-dw@davidwei.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/devmem.c

@@ -30,6 +30,11 @@ static DEFINE_XARRAY_FLAGS(net_devmem_dmabuf_bindings, XA_FLAGS_ALLOC1);
 
 static const struct memory_provider_ops dmabuf_devmem_ops;
 
+bool net_is_devmem_iov(struct net_iov *niov)
+{
+	return niov->pp->mp_ops == &dmabuf_devmem_ops;
+}
+
 static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool,
 					       struct gen_pool_chunk *chunk,
 					       void *not_used)

net/core/devmem.h

@@ -115,6 +115,8 @@ struct net_iov *
 net_devmem_alloc_dmabuf(struct net_devmem_dmabuf_binding *binding);
 void net_devmem_free_dmabuf(struct net_iov *ppiov);
 
+bool net_is_devmem_iov(struct net_iov *niov);
+
 #else
 struct net_devmem_dmabuf_binding;
 
@@ -163,6 +165,11 @@ static inline u32 net_devmem_iov_binding_id(const struct net_iov *niov)
 {
 	return 0;
 }
+
+static inline bool net_is_devmem_iov(struct net_iov *niov)
+{
+	return false;
+}
 #endif
 
 #endif /* _NET_DEVMEM_H */

net/ipv4/tcp.c

@@ -2476,6 +2476,11 @@ static int tcp_recvmsg_dmabuf(struct sock *sk, const struct sk_buff *skb,
 			}
 
 			niov = skb_frag_net_iov(frag);
+			if (!net_is_devmem_iov(niov)) {
+				err = -ENODEV;
+				goto out;
+			}
+
 			end = start + skb_frag_size(frag);
 			copy = end - offset;