Xen Hypervisor Does Not Boot with 255 or more CPUs (threads)

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Environment

SUSE Linux Enterprise Server 15 SP1

Situation

The Xen Hypervisor does not boot on machines with 255 or more CPUs (threads) such as the

AMD EPYC™ 7002 Series Processors.

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Resolution

Work is currently on going in the upstream open source Xen project to permanently address the issue with new processors that have more than 255 CPUs and will be addressed in a future update to SUSE Linux Enterprise Server.

A temporary solution is to disable AMD SMT in the BIOS of systems. This will result in at most 128 CPUs (cores) being seen by the Xen Hypervisor.

Note: This is as long as in this reduced core mode that the BIOS does not put the system into x2APIC mode. This may vary between hardware system vendors.

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Additional Information

Disclaimer

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