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

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

On 11/22/23 18:03, Laszlo Ersek wrote:
> 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.

sorry, small mistake: when writing this, I was already looking at the
final state of the tree. Right after this patch is applied, only
ApInitializeSync() exists!

But that fact only makes my argument stronger -- so my R-b for this
patch stands.

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

Thanks
Laszlo



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