Re: [edk2-devel] [Patch V2 2/3] UefiCpuPkg/MpInitLib: Detect microcode and store MTRR when CpuCount > 1

["Laszlo Ersek" <lersek@redhat.com>]

On 11/21/23 08:39, Yuanhao Xie wrote:
> Detect and apply Microcode on BSP, store BSP's MTRR setting only when
> CpuCount > 1.
> 
> The purpose of this patch is to enhance the review process.
> The separation in this patch is aimed at facilitating a more
> straightforward review, with the ultimate goal of eliminating the
> microcode loading functionality for the second time Mp initialization
> 
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Rahul Kumar <rahul1.kumar@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Yuanhao Xie <yuanhao.xie@intel.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index e8ffb99874..bb5d4188f0 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -2236,19 +2236,19 @@ MpInitLibInitialize (
>      ShadowMicrocodeUpdatePatch (CpuMpData);
>    }
>  
> -  //
> -  // Detect and apply Microcode on BSP
> -  //
> -  MicrocodeDetect (CpuMpData, CpuMpData->BspNumber);
> -  //
> -  // Store BSP's MTRR setting
> -  //
> -  MtrrGetAllMtrrs (&CpuMpData->MtrrTable);
> -
>    //
>    // Wakeup APs to do some AP initialize sync (Microcode & MTRR)
>    //
>    if (CpuMpData->CpuCount > 1) {
> +    //
> +    // Detect and apply Microcode on BSP
> +    //
> +    MicrocodeDetect (CpuMpData, CpuMpData->BspNumber);
> +    //
> +    // Store BSP's MTRR setting
> +    //
> +    MtrrGetAllMtrrs (&CpuMpData->MtrrTable);
> +
>      if (MpHandOff != NULL) {
>        //
>        // Only needs to use this flag for DXE phase to update the wake up

I can't very well gauge the effect that this patch has on
MicrocodeDetect(). MicrocodeDetect() is a function that is not obvious
to me. However, microcode detection is disabled on OVMF, both via HOB
and via PCD (zero region size). So, I have nothing against *restricting*
microcode detection "further".

Regarding MtrrTable: it seems that this field is only consumed in
ApMtrrSync() and ApInitializeSync(). I suppose those functions never run
when CpuMpData->CpuCount is 1. Thus restricting MtrrGetAllMtrrs() should
be fine as well.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>



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