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]>
