Hi,

On 3/10/26 10:18 AM, Paolo Abeni wrote:

This is an AI-generated review of your patch. The human sending this
email has considered the AI review valid, or at least plausible.

For local reproduction steps see https://netdev-ai.bots.linux.dev/ai-local.html
---

quoted

@@ -581,11 +585,21 @@ int vsock_assign_transport(struct vsock_sock *vsk, struct vsock_sock *psk)
 	case SOCK_SEQPACKET:
 		if (vsock_use_local_transport(remote_cid))
 			new_transport = transport_local;
-		else if (remote_cid <= VMADDR_CID_HOST || !transport_h2g ||
+		else if (remote_cid <= VMADDR_CID_HOST ||
 			 (remote_flags & VMADDR_FLAG_TO_HOST))
 			new_transport = transport_g2h;
-		else
+		else if (transport_h2g &&
+			 (!transport_h2g->has_remote_cid ||
+			  transport_h2g->has_remote_cid(vsk, remote_cid)))
+			new_transport = transport_h2g;
+		else if (sock_net(sk)->vsock.g2h_fallback &&
+			 transport_g2h && transport_g2h->has_remote_cid &&
+			 transport_g2h->has_remote_cid(vsk, remote_cid)) {
+			vsk->remote_addr.svm_flags |= VMADDR_FLAG_TO_HOST;
+			new_transport = transport_g2h;
+		} else {
 			new_transport = transport_h2g;
+		}
 		break;

The old code had `!transport_h2g` in the second else-if condition at line
-583, which routed all CID > VMADDR_CID_HOST traffic to transport_g2h when
no H2G transport was loaded. The new code removes this check.

When transport_h2g is NULL (no H2G transport loaded) and the G2H transport
does not implement has_remote_cid (as is the case for VMCI and Hyper-V
transports), what happens?

The G2H fallback branch at line +596 requires
`transport_g2h->has_remote_cid` to be non-NULL. If it's NULL, the
short-circuit evaluation skips this branch and executes the final else at
line +601, setting `new_transport = transport_h2g` (which is NULL),
ultimately returning -ENODEV.

The commit message explicitly states the intent to preserve the existing
no-H2G fallback behavior. Does this implementation break it for G2H
transports that do not implement the new optional has_remote_cid callback?

This affects VMCI and Hyper-V environments: when no H2G transport is
loaded, CID > 2 connections that previously fell back to G2H now get
ENODEV.

Other comments from AI looked like nit picking to me, but the above one
looks relevant. I forwarded verbatim all the feedback for completeness.

/P