tcp: RX path for devmem TCP

In tcp_recvmsg_locked(), detect if the skb being received by the user
is a devmem skb. In this case - if the user provided the MSG_SOCK_DEVMEM
flag - pass it to tcp_recvmsg_devmem() for custom handling.

tcp_recvmsg_devmem() copies any data in the skb header to the linear
buffer, and returns a cmsg to the user indicating the number of bytes
returned in the linear buffer.

tcp_recvmsg_devmem() then loops over the unaccessible devmem skb frags,
and returns to the user a cmsg_devmem indicating the location of the
data in the dmabuf device memory. cmsg_devmem contains this information:

1. the offset into the dmabuf where the payload starts. 'frag_offset'.
2. the size of the frag. 'frag_size'.
3. an opaque token 'frag_token' to return to the kernel when the buffer
is to be released.

The pages awaiting freeing are stored in the newly added
sk->sk_user_frags, and each page passed to userspace is get_page()'d.
This reference is dropped once the userspace indicates that it is
done reading this page.  All pages are released when the socket is
destroyed.

Signed-off-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://patch.msgid.link/20240910171458.219195-10-almasrymina@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/net/core/devmem.h b/net/core/devmem.h
index b1db4877cff9..76099ef9c482 100644
--- a/net/core/devmem.h
+++ b/net/core/devmem.h
@@ -91,6 +91,19 @@ net_iov_binding(const struct net_iov *niov)
 	return net_iov_owner(niov)->binding;
 }
 
+static inline unsigned long net_iov_virtual_addr(const struct net_iov *niov)
+{
+	struct dmabuf_genpool_chunk_owner *owner = net_iov_owner(niov);
+
+	return owner->base_virtual +
+	       ((unsigned long)net_iov_idx(niov) << PAGE_SHIFT);
+}
+
+static inline u32 net_iov_binding_id(const struct net_iov *niov)
+{
+	return net_iov_owner(niov)->binding->id;
+}
+
 static inline void
 net_devmem_dmabuf_binding_get(struct net_devmem_dmabuf_binding *binding)
 {
@@ -153,6 +166,15 @@ static inline void net_devmem_free_dmabuf(struct net_iov *ppiov)
 {
 }
 
+static inline unsigned long net_iov_virtual_addr(const struct net_iov *niov)
+{
+	return 0;
+}
+
+static inline u32 net_iov_binding_id(const struct net_iov *niov)
+{
+	return 0;
+}
 #endif
 
 #endif /* _NET_DEVMEM_H */