Re: [edk2-devel] [PATCH v1 2/2] UefiCpuPkg/BaseXApicX2ApicLib: Implements AMD extended cpu topology

["Gerd Hoffmann" <kraxel@redhat.com>]

On Tue, Jan 16, 2024 at 12:31:21PM +0530, Abdul Lateef Attar wrote:
> From: Abdul Lateef Attar <AbdulLateef.Attar@amd.com>
> 
> This patch adds support for AMD's new extended topology.
> If processor supports CPUID 80000026 leaf then obtain
> the topology information using new method.

> +  /// Check if extended toplogy supported
> +  AsmCpuid (CPUID_EXTENDED_FUNCTION, &MaxExtendedCpuIdIndex, NULL, NULL, NULL);
> +  if (MaxExtendedCpuIdIndex < AMD_CPUID_EXTENDED_TOPOLOGY) {
> +    GetProcessorLocationByApicId (InitialApicId, Package, Core, Thread);
> +    return;
> +  }

Sure this is correct?

On Intel processors checking MaxExtendedCpuIdIndex alone is not enough,
see commit 170d4ce8e90a ("UefiCpuPkg/BaseXApicX2ApicLib: fix
CPUID_V2_EXTENDED_TOPOLOGY detection")

Especially in virtual machines it can happen that the vCPU supports
extended cpuid leaf N but does not support N-1, so checking
MaxExtendedCpuIdIndex alone looks rather fragile to me.

take care,
  Gerd



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