(DO NOT MERGE: WILL UPSTREAM THIS CHANGE FIRST) get connection-id from device tree

[hargar19]

The connection-id determines which hypervisor communication channel the guest should use to talk to the VMBus host. Get this value from device tree instead of kernel boot arguments.

Below data shows already existing property under the vmbus device tree node with the compatible id "microsoft,message-connection-id":

cd /sys/firmware/devicetree/base/bus/vmbus

/sys/firmware/devicetree/base/bus/vmbus # hexdump microsoft,message-connection-i
d
0000000 8000 7400
0000004

connection-id value from dmesg logs after the code change:
0.630151] hv_vmbus: VMBus message connection ID: 8388724

The hexdump shows: 00 80 00 74
0x00800074 = 8388724 (decimal)

[Copilot]

Pull Request Overview

This PR updates the VMBus driver to source the connection ID from the device tree rather than using a module parameter, ensuring consistency with device configuration.

• Updated vmbus_drv.c to read the connection ID property from the device tree.
• Revised vmbus_connection handling in connection.c by removing the module parameter and adding default logic.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
drivers/hv/vmbus_drv.c	Added code to read and log the connection ID from the device tree.
drivers/hv/connection.c	Removed outdated module parameter and updated default connection ID assignment logic.

[hargar19]

Work-item for this PR https://microsoft.visualstudio.com/OS/_workitems/edit/48864356/

[romank-msft]

@hargar19 we should merge this. Without it, this commit microsoft/openvmm#1501 breaks guests with VMBus relay due to

    // If we're isolated we can't trust the host-provided cmdline
    if can_trust_host {
        let old_cmdline = &partition_info.cmdline;

        // HACK: See if we should set the vmbus connection id via kernel
        // commandline. It may already be set, and we don't want to set it again.
        //
        // This code will be removed when the kernel supports setting connection id
        // via device tree.
        if !old_cmdline.contains("hv_vmbus.message_connection_id=") {
            write!(
                cmdline,
                "hv_vmbus.message_connection_id=0x{:x} ",
                partition_info.vmbus_vtl2.connection_id
            )?;
        }

        // Prepend the computed parameters to the original command line.
        cmdline.write_str(old_cmdline)?;
    }
``` in the bootshim.

[hargar19]

@romank-msft I have sent this patch upstream https://lore.kernel.org/all/SN6PR02MB4157F2C0674B85C7206E6047D47CA@SN6PR02MB4157.namprd02.prod.outlook.com/
Once the patch is accepted, we will upgrade the HCL kernel to include it. This PR will be discarded.