Re: [PATCH v2] Drivers: hv: vmbus: add VTL2 redirect connection ID

On 7/17/2026 5:48 AM, Hardik Garg wrote:
> VMBus sends CHANNELMSG_INITIATE_CONTACT through a Hyper-V message
> connection ID. Older protocol versions use VMBUS_MESSAGE_CONNECTION_ID,
> while protocol version 5.0 and newer normally use
> VMBUS_MESSAGE_CONNECTION_ID_4.
> 
> For a VTL2 kernel using VMBus protocol 5.0 or newer, the host
> may expect INITIATE_CONTACT on either the redirect connection ID or
> VMBUS_MESSAGE_CONNECTION_ID_4. There is no capability indication that
> identifies which ID is active, so the driver must determine it at runtime.
> 
> During VMBus negotiation, the redirect ID is tried first because it is
> used by VTL2 configurations with VMBus redirection enabled. If the
> redirect ID is unavailable, the host rejects it synchronously with
> HV_STATUS_INVALID_CONNECTION_ID, allowing fallback to the standard ID.
> 
> Return a distinct error for an invalid Initiate Contact connection ID so
> this fallback does not mask other post-message failures or
> protocol-version rejections. Preserve the existing connection ID
> selection for older protocol versions or when running below VTL2.
> 
> Signed-off-by: Hardik Garg <[email protected]>
> ---
> 

Reviewed-by: Naman Jain <[email protected]>