XEN: Fully virtual DomU's fail to load or Windows "blue screens"

This document (7000036) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 10 Support Pack 1

SUSE Virtual Machine Driver Pack for Xen

Situation

Fully virtual DomU's, such as Windows, fail to load with out any error messages.
Windows "blue screens" with "lost ticks" message with or without the Virtual Machine Driver Pack loaded
Windows "blue screens" with other messages with the Virtual Machine Driver Pack loaded

Resolution

Fully virtual Windows DomU's may fail to load if they have multiprocessors enabled in their configuration file. Unlike other operating systems, Windows queries a register on the front side bus in order to determine whether or not there are multiple processors. In some cases fully-virtual Windows machines, especially Windows Server 2003 R2, will load up only to blue screen later in the load process.

In SLES 10 SP1, multiple vCPU (i.e. SMP) are NOT supported. However in SLES 10 SP2, multiple vCPU's are supported.

recommendation: update to SLES 10 SP2

SLES 10 SP2 introduced SMP vCPU support for fully-virtual DomU's. This support allows users wishing to have more than a single vCPU with out the blue screen and boot issues. Per the documentation, SUSE supports up to 4 vCPUs. However, SUSE strongly recommends the use of the Virtual Machine Driver Pack when using multiple vCPU's for Windows systems that have been virtualized. SUSE also introduced significant features that are attractive for enterprise customers making the update attractive.

Please see TID 7000608, XEN: Critical considerations when updating from SLES 10 SP1 to SLES 10 SP2 when updating.

If you are unable to update to SLES 10 SP2, or elect to remain on SLES 10 SP1, the following methods will aide you in recovering from the error. However, please be aware that SUSE will not offer full support, including bug fixes and problem determination for SLES 10 SP1 systems in early November 2008. Those who seek support from SUSE may be required to update to SLES 10 SP2 after early November 2008.

method 1: unmanaged domains and domains managed by a cluster
This method assumes that the configuration file is read each time a virtual machine is started. The virtual machine is not started using "xm start", YaST or "virt-manager". This is the only option for DomU's that are managed by Cluster Services and Linux Heartbeat.

Go to /etc/xen/vm
Locate the configuration file
Back it up (in case you need it again)
Open the file for editing
Locate the line reading:
vcpus=2
Change the vpcu's to 1
vcpus=1
Save the file and close it
Test to make sure that the VM starts
xm create NAME_OF_FILE

method 2: use method 1 and import the changes
This method assumes that the DomU configuration has not been modified or altered using "xm" commands, YaST, or "virt-manager." If you follow this method and you have manipulated the configuration via one of the mentioned methods, the virtual machines hardware profile will be lost

Delete the configuration from the Xen store
xm delete NAME_OF_DOMU
Follow method 1.
Once you are satisfied that the DomU starts in method 1, import the configuration
xm new -f NAME_OF_DOMU

method 3: export configuration from Xen store
This method is only recommended when you have made configuration changes using "xm" commands, YaST, or "virt-manager"; if you have not made changes since the initial installation, FOLLOW METHOD 2. This method involves exporting the Python configuration from the Xen store, changing it and reimporting it. This method does take longer to implement and cannot be tested with out reimporting the configuration back into the Xen store.
Replace "SLES10" with the name of the DomU

Export the configuration of the DomU to a file
xm list -l SLES10 > SLES10.py
Backup the file, in case an error happens
Open the file for editing
Locate the following line (or similar line)
(vcpus 2)
Change it to:
(vcpus 1)
Save the file and close it
Re-import the changes. The capital -F is important.
xm new -F SLES10.py
Start the DomU

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.