[edk2-devel] MP services reports incorrect number of CPUs under QEMU without KVM

[nicholasbishop at gmail.com]

When using EFI_MP_SERVICES_PROTOCOL.GetNumberOfProcessors to get the number of processors, I've found that when running in QEMU I only get the correct value if KVM is enabled. If KVM is disabled, the number of processors is always reported as 1.

With debug logging enabled, I noticed a difference in the output from MaxCpuCountInitialization.

With `-enable-kvm -smp 4` it logs this:
MaxCpuCountInitialization: BootCpuCount=4 mMaxCpuCount=4

But with just `-smp 4`, it logs this:
MaxCpuCountInitialization: QEMU v2.7 reset bug: BootCpuCount=4 Present=0
MaxCpuCountInitialization: BootCpuCount=0 mMaxCpuCount=1

I'm not sure if this indicates a bug in QEMU or OVMF. Incidentally the "QEMU v2.7" is hardcoded in OvmfPkg/PlatformPei/Platform.c, I'm actually testing under QEMU 6.1.0.

Test code: https://github.com/nicholasbishop/edk2/blob/af920578e822cdeef0204e39df560f4a1f4bb537/Bug/Bug.c


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