From mboxrd@z Thu Jan  1 00:00:00 1970
Subject: MP services reports incorrect number of CPUs under QEMU without KVM
To: devel@edk2.groups.io
From: nicholasbishop@gmail.com
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Date: Sat, 05 Mar 2022 12:33:17 -0800
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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 a=
lways reported as 1.

With debug logging enabled, I noticed a difference in the output from MaxCp=
uCountInitialization.

With `-enable-kvm -smp 4` it logs this:
MaxCpuCountInitialization: BootCpuCount=3D4 mMaxCpuCount=3D4

But with just `-smp 4`, it logs this:
MaxCpuCountInitialization: QEMU v2.7 reset bug: BootCpuCount=3D4 Present=3D=
0
MaxCpuCountInitialization: BootCpuCount=3D0 mMaxCpuCount=3D1

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

Test code: https://github.com/nicholasbishop/edk2/blob/af920578e822cdeef020=
4e39df560f4a1f4bb537/Bug/Bug.c

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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 a=
lways reported as 1.<br /><br />With debug logging enabled, I noticed a dif=
ference in the output from MaxCpuCountInitialization.<br /><br />With `-ena=
ble-kvm -smp 4` it logs this:<br />MaxCpuCountInitialization: BootCpuCount=
=3D4 mMaxCpuCount=3D4<br /><br />But with just `-smp 4`, it logs this:<br /=
>MaxCpuCountInitialization: QEMU v2.7 reset bug: BootCpuCount=3D4 Present=
=3D0<br />MaxCpuCountInitialization: BootCpuCount=3D0 mMaxCpuCount=3D1<br /=
><br />I'm not sure if this indicates a bug in QEMU or OVMF. Incidentally t=
he "QEMU v2.7" is hardcoded in OvmfPkg/PlatformPei/Platform.c, I'm actually=
 testing under QEMU 6.1.0.<br /><br />Test code: https://github.com/nichola=
sbishop/edk2/blob/af920578e822cdeef0204e39df560f4a1f4bb537/Bug/Bug.c

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