[Firmware Bug]: CPU52: APIC id mismatch. Firmware: 34 APIC: 40

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Environment

SUSE Linux Enterprise Server 12 SP4 (LTSS)
Microsoft Azure Virtual Machines

Situation

System is running on top of Microsoft Azure and these messages can be seen in the logs:

2020-11-08T09:32:59.603656+00:00 hec45v122410 kernel: [0.004000] [Firmware Bug]: CPU52: APIC id mismatch. Firmware: 34 APIC: 40
2020-11-08T09:32:59.603656+00:00 hec45v122410 kernel: [0.120329] #53
2020-11-08T09:32:59.603657+00:00 hec45v122410 kernel: [0.004000] [Firmware Bug]: CPU53: APIC id mismatch. Firmware: 35 APIC: 41
2020-11-08T09:32:59.603660+00:00 hec45v122410 kernel: [0.125622] #54
2020-11-08T09:32:59.603661+00:00 hec45v122410 kernel: [0.004000] [Firmware Bug]: CPU54: APIC id mismatch. Firmware: 36 APIC: 42
2020-11-08T09:32:59.603661+00:00 hec45v122410 kernel: [0.130967] #55
2020-11-08T09:32:59.603661+00:00 hec45v122410 kernel: [0.004000] [Firmware Bug]: CPU55: APIC id mismatch. Firmware: 37 APIC: 43
2020-11-08T09:32:59.603662+00:00 hec45v122410 kernel: [0.134924] #56
2020-11-08T09:32:59.603662+00:00 hec45v122410 kernel: [0.004000] [Firmware Bug]: CPU56: APIC id mismatch. Firmware: 38 APIC: 44

Resolution

The reported kernel messages are harmless.

Cause

These errors are benign and can be ignored:

 [Firmware Bug]: CPU52: APIC id mismatch. Firmware: 34 APIC: 40

They occur in any Azure VM that has multiple NUMA nodes and where the number of vCPUs in a NUMA node is not a power of 2.
In this case the M208ms_v2 VM size has 208 vCPUs, with 52 vCPUs in each of 4 NUMA nodes. 52 is not a power of 2, so the errors are generated.
The root cause is the way Hyper-V sets up some ACPI tables in the guest VM.

Disclaimer

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