Re: [edk2-devel] [Patch V3 1/3] UefiCpuPkg/MpInitLib: Eliminate redundant microcode loading in DXE.

["Ni, Ray" <ray.ni@intel.com>]

> -  MicrocodeDetect (CpuMpData, ProcessorNumber);
> -  //
> -  // Sync BSP's MTRR table to AP
> +  // Synchronizing the MTRR table to the AP is always essential.
> +  // During the DXE phase, it cannot be omitted like loading microcode,
> +  // as the PEI and DXE may be in different bit modes.


"as the PEI and DXE may be in different bit modes" is not the reason that
MTRR sync needs to be performed in DXE phase.

The reason is some code might change MTRR on BSP only after CpuMp PPI
service is not available and before CpuMp Protocol is available.
That is in early DXE phase before CpuMp protocol is installed.

>    //
>    MtrrSetAllMtrrs (&CpuMpData->MtrrTable);
>  }


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