On 10.03.26 10:26, Paolo Abeni wrote:
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
---
@@ -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.
Yes, this is on purpose. Instead of having bi-modality based on whether
the vhost_vsock kernel module is loaded, we now clearly define that with
the sysctl off, you get the same mode that "vhost_vsock is loaded" gave
you before. The oddball case of "vhost_vsock is not loaded" that meant
everything goes to the G2H transport and confused users is really not
worth keeping IMHO. It's replaced by the auto-fallback logic.
Broadcom also mentioned that G2H for CID > 2 does not exist. IIUC
Hyper-V also does not support CID > 2.
Alex
Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christof Hellmis, Andreas Stieger
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