EPYC 7003/7002 shows only 255 CPUs online

Solution Unverified - Updated -

Issue

  • System has 256 logical processors (0 - 255)
  • However, lscpu shows only 255 CPUs are online, 1 CPU is offline
# lscpu
...
CPU(s):                256
On-line CPU(s) list:   0-254
Off-line CPU(s) list:  255
...

Environment

  • Red Hat Enterprise Linux 7
  • EPYC 7003/7002 Series Processors
  • Input-Output Memory Management Unit (IOMMU) disabled

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