Re: [edk2-devel] [PATCH v2 1/1] UefiCpuPkg/MpInitLib: Reduce reset vector memory pressure

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 9/25/20 11:09 AM, Brian J. Johnson wrote:
> On 9/24/20 1:22 AM, Laszlo Ersek wrote:
>> - I don't remember if it's required that the APIC ID space be densely
>> populated. For example, if we have a topology with 7 possible (=
>> maximum) logical CPUs, I'm unsure if a spec forbids any of those CPUs
>> from having APIC ID 7. That could cause a problem in
>> MpInitLibSevEsAPReset(), I assume.
> 
> FWIW, there are many bare metal processors with non-contiguous APIC IDs. 
>   Intel puts the socket ID in the upper bits of the APIC ID.  So if the 
> socket doesn't have a power-of-two number of cores, there is always a 
> gap.  Plus, the BSP doesn't always have APIC ID 0 -- it depends on which 
> physical cores passed the manufacturing tests for that particular part. 
> That has broken various kernels, BIOSes, and other software at times. So 
> it's best not to make assumptions.
> 
> I don't know if that applies to VMs, though.  The standards may be 
> different (if there are any standards at all in that area.)

Yes, I'm working on a patch to use GetProcessorNumber() instead of using 
the APIC ID.

Thanks,
Tom

>