Some virtual servers crash with kernel panics on startup on Xen compute resources to get access to all CPUs of the compute resource despite the configuration made in the UI.
Compute resources - Xen
All Linux-based virtual servers with kernel < 2.6.32
Install a newer kernel >= 2.6.32. To install the newer kernel, boot the virtual server in the recovery mode. Refer to the Change Windows Virtual Server Password From Recovery Mode page to prepare a chroot environment. Follow steps 1–6.
Switching to use the libvirt toolstack instead of xl on Xen compute resources. The XML config is formed in the way that virtual servers get access to all CPUs available on the compute resource but limited to a number set in the UI. It allows supporting hot resize features. However, old kernels are unable to serve more than 32 vCPUs that are passed to them.
A virtual server was configured with one core
<vcpu current=\"1\">32</vcpu>, but you may see that the virtual server got 32 vCPUs on the compute resource:
[root@xenhv~]# xl list Name ID Mem VCPUs State Time(s) ioz4zf4wczatn0 6 1024 32 -b---- 13058.3