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Update Viridian instructions #416

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16 changes: 16 additions & 0 deletions docs/troubleshooting/windows-pv-tools.md
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Expand Up @@ -188,3 +188,19 @@ See the [XenClean guide](/vms/#fully-removing-xen-pv-drivers-with-xenclean) for
:::note
You will need to reinstall the management agent.
:::

## Windows Server 2025 hangs randomly with 0% CPU

### Cause

This can be due to the Viridian synthetic timer feature being disabled on the guest.

### Solution

First, check that [Viridian extensions are all enabled on your VM](/vms/#enabling-viridian-extensions).
If you've set boot parameters to disable the synthetic timer, they need to be reverted:

```
bcdedit /deletevalue "{current}" useplatformclock
bcdedit /deletevalue "{current}" useplatformtick
```
23 changes: 9 additions & 14 deletions docs/vms/vms.md
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Expand Up @@ -340,20 +340,15 @@ Viridian extensions —referred to as "Viridian enlightenments" by Microsoft—

Viridian enlightenments are enabled by default on Windows VM templates included with XCP-ng.

To enable Viridian enlightenments for other non-Windows VM templates, you need to:

1. **Enable Viridian**. To do this, run `xe vm-param-set uuid=<vm uuid> platform:viridian=true` in your VM.
2. **Enable the extra Viridian parameters** necessary for your template to run optimally with Windows. To do this, run the same `xe` command in your VM, but change the arguments with the following:

```
"device_id": "0002", // ID used by XCP-ng to detect Windows VMs
"viridian": "true",
"viridian_time_ref_count": "true",
"viridian_reference_tsc": "true",
"viridian_apic_assist": "true",
"viridian_crash_ctl": "true",
"viridian_stimer": "true"
```
To enable Viridian enlightenments for other non-Windows VM templates, simply run the following command:

```
xe vm-param-set uuid=<vm-uuid> platform:device_id=0002 platform:viridian=true platform:viridian_time_ref_count=true platform:viridian_reference_tsc=true platform:viridian_apic_assist=true platform:viridian_crash_ctl=true platform:viridian_stimer=true
```

:::warning
Do not set the device ID on VMs with Xen PV drivers installed. Changing the device ID may cause old Xen PV drivers to fail booting.
:::

:::

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