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Pinned CPUs must be sequential starting from boot vCPU0

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Abstract

The PowerPC (PPC) architecture enforces a strict sequential ordering constraint for virtual central processing unit (CPU) allocation. Non hot-pluggable CPUs must occupy contiguous positions beginning at vCPU 0, with hot-pluggable CPUs that are allocated sequentially thereafter. Deviation from this contiguous arrangement, specifically, the introduction of gaps or staggered positioning among non hot-pluggable CPUs undermines fundamental architectural assumptions and might precipitate critical system failures. To ensure system stability, you can keep non hot-pluggable or pinned CPUs in sequential ordering from vCPU 1. vCPU 0 is non hot-pluggable by default.

Content

Linux Releases Affected

All

IBM Systems Affected

KVM on PowerVM

Symptoms

Non-contiguous hot-pluggable vCPU configuration triggers assertion failure.

Workaround

Contiguous sequential ordering of pinned vCPUs from boot vCPU 1 can prevent this issue.

Fix Outlook

The fix for this issue will be included in a later release.

I/O device impacted

N/A

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Document Information

Modified date:
04 May 2026

UID

ibm17269908

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