Re: [edk2-devel] [PATCH V2] UefiCpuPkg PiSmmCpuDxeSmm: Reduce SMRAM consumption in CpuS3.c

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

On 01/06/21 18:56, Laszlo Ersek wrote:
> On 01/06/21 07:48, Zeng, Star wrote:
>> This patch makes two refinements to reduce SMRAM consumption in CpuS3.c.
>> 1. Only do CopyRegisterTable() when register table is not empty,
>>   IsRegisterTableEmpty() is created to check whether the register table
>>   is empty or not.
>>
>>   Take empty PreSmmInitRegisterTable as example, about 24K SMRAM consumption
>>   could be reduced when mAcpiCpuData.NumberOfCpus=1024.
>>   sizeof (CPU_REGISTER_TABLE) = 24
>>   mAcpiCpuData.NumberOfCpus = 1024 = 1K
>>   mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE) = 24K
>>
>> 2. Only copy table entries buffer instead of whole buffer.
>>   AllocatedSize in SourceRegisterTableList is the whole buffer size.
>>   Actually, only the table entries buffer needs to be copied, and the size
>>   is TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY).
>>
>>   Take AllocatedSize=0x1000=4096, TableLength=100 and NumberOfCpus=1024 as example,
>>   about 1696K SMRAM consumption could be reduced.
>>   sizeof (CPU_REGISTER_TABLE_ENTRY) = 24
>>   TableLength = 100
>>   TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY) = 2400
>>   AllocatedSize = 0x1000 = 4096
>>   AllocatedSize - TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY) = 4096 - 2400 = 1696
>>   NumberOfCpus = 1024 = 1K
>>   NumberOfCpus * (AllocatedSize - TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY)) = 1696K
>>
>> This patch also corrects the CopyRegisterTable() function description.
>>
>> Signed-off-by: Star Zeng <star.zeng@intel.com>
>> Cc: Ray Ni <ray.ni@intel.com>
>> Cc: Eric Dong <eric.dong@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> ---
>>  UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c | 71 +++++++++++++++++++++++--------
>>  1 file changed, 54 insertions(+), 17 deletions(-)
>>
>> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
>> index 9592430636ec..9b1f952c8a74 100644
>> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
>> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
>> @@ -1,7 +1,7 @@
>>  /** @file
>>  Code for Processor S3 restoration
>>  
>> -Copyright (c) 2006 - 2020, Intel Corporation. All rights reserved.<BR>
>> +Copyright (c) 2006 - 2021, Intel Corporation. All rights reserved.<BR>
>>  SPDX-License-Identifier: BSD-2-Clause-Patent
>>  
>>  **/
>> @@ -487,6 +487,9 @@ SetRegister (
>>    } else {
>>      RegisterTables = (CPU_REGISTER_TABLE *)(UINTN)mAcpiCpuData.RegisterTable;
>>    }
>> +  if (RegisterTables == NULL) {
>> +    return;
>> +  }
>>  
>>    InitApicId = GetInitialApicId ();
>>    RegisterTable = NULL;
>> @@ -948,7 +951,7 @@ InitSmmS3ResumeState (
>>  }
>>  
>>  /**
>> -  Copy register table from ACPI NVS memory into SMRAM.
>> +  Copy register table from non-SMRAM into SMRAM.
>>  
>>    @param[in] DestinationRegisterTableList  Points to destination register table.
>>    @param[in] SourceRegisterTableList       Points to source register table.
>> @@ -967,7 +970,8 @@ CopyRegisterTable (
>>  
>>    CopyMem (DestinationRegisterTableList, SourceRegisterTableList, NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
>>    for (Index = 0; Index < NumberOfCpus; Index++) {
>> -    if (DestinationRegisterTableList[Index].AllocatedSize != 0) {
>> +    if (DestinationRegisterTableList[Index].TableLength != 0) {
>> +      DestinationRegisterTableList[Index].AllocatedSize = DestinationRegisterTableList[Index].TableLength * sizeof (CPU_REGISTER_TABLE_ENTRY);
>>        RegisterTableEntry = AllocateCopyPool (
>>          DestinationRegisterTableList[Index].AllocatedSize,
>>          (VOID *)(UINTN)SourceRegisterTableList[Index].RegisterTableEntry
>> @@ -978,6 +982,31 @@ CopyRegisterTable (
>>    }
>>  }
>>  
>> +/**
>> +  Check whether the register table is empty or not.
>> +
>> +  @param[in] RegisterTable  Point to the register table.
>> +
>> +  @retval TRUE              The register table is empty.
>> +  @retval FALSE             The register table is not empty.
>> +**/
>> +BOOLEAN
>> +IsRegisterTableEmpty (
>> +  IN CPU_REGISTER_TABLE     *RegisterTable,
>> +  IN UINT32                 NumberOfCpus
>> +  )
>> +{
>> +  UINTN                     Index;
>> +
>> +  for (Index = 0; Index < NumberOfCpus; Index++) {
>> +    if (RegisterTable[Index].TableLength != 0) {
>> +      return FALSE;
>> +    }
>> +  }
>> +
>> +  return TRUE;
>> +}
>> +
>>  /**
>>    Get ACPI CPU data.
>>  
>> @@ -1032,23 +1061,31 @@ GetAcpiCpuData (
>>  
>>    CopyMem ((VOID *)(UINTN)mAcpiCpuData.IdtrProfile, (VOID *)(UINTN)AcpiCpuData->IdtrProfile, sizeof (IA32_DESCRIPTOR));
>>  
>> -  mAcpiCpuData.PreSmmInitRegisterTable = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePool (mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
>> -  ASSERT (mAcpiCpuData.PreSmmInitRegisterTable != 0);
>> +  if (!IsRegisterTableEmpty ((CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->PreSmmInitRegisterTable, mAcpiCpuData.NumberOfCpus)) {
>> +    mAcpiCpuData.PreSmmInitRegisterTable = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePool (mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
>> +    ASSERT (mAcpiCpuData.PreSmmInitRegisterTable != 0);
>>  
>> -  CopyRegisterTable (
>> -    (CPU_REGISTER_TABLE *)(UINTN)mAcpiCpuData.PreSmmInitRegisterTable,
>> -    (CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->PreSmmInitRegisterTable,
>> -    mAcpiCpuData.NumberOfCpus
>> -    );
>> +    CopyRegisterTable (
>> +      (CPU_REGISTER_TABLE *)(UINTN)mAcpiCpuData.PreSmmInitRegisterTable,
>> +      (CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->PreSmmInitRegisterTable,
>> +      mAcpiCpuData.NumberOfCpus
>> +      );
>> +  } else {
>> +    mAcpiCpuData.PreSmmInitRegisterTable = 0;
>> +  }
>>  
>> -  mAcpiCpuData.RegisterTable = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePool (mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
>> -  ASSERT (mAcpiCpuData.RegisterTable != 0);
>> +  if (!IsRegisterTableEmpty ((CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->RegisterTable, mAcpiCpuData.NumberOfCpus)) {
>> +    mAcpiCpuData.RegisterTable = (EFI_PHYSICAL_ADDRESS)(UINTN)AllocatePool (mAcpiCpuData.NumberOfCpus * sizeof (CPU_REGISTER_TABLE));
>> +    ASSERT (mAcpiCpuData.RegisterTable != 0);
>>  
>> -  CopyRegisterTable (
>> -    (CPU_REGISTER_TABLE *)(UINTN)mAcpiCpuData.RegisterTable,
>> -    (CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->RegisterTable,
>> -    mAcpiCpuData.NumberOfCpus
>> -    );
>> +    CopyRegisterTable (
>> +      (CPU_REGISTER_TABLE *)(UINTN)mAcpiCpuData.RegisterTable,
>> +      (CPU_REGISTER_TABLE *)(UINTN)AcpiCpuData->RegisterTable,
>> +      mAcpiCpuData.NumberOfCpus
>> +      );
>> +  } else {
>> +    mAcpiCpuData.RegisterTable = 0;
>> +  }
>>  
>>    //
>>    // Copy AP's GDT, IDT and Machine Check handler into SMRAM.
>>
> 
> This patch is a step in the right direction, but, IMO, it can be improved.
> 
> The IsRegisterTableEmpty() function should also handle the case when the
> "RegisterTable" parameter is NULL. The function should then also return
> TRUE.
> 
> And then, two more patches would be nice:
> 
> 
> (2) The register table allocation in
> "UefiCpuPkg/CpuS3DataDxe/CpuS3Data.c" should be removed.
> 
> Right now, the code there allocates memory just so it can set the
> "TableLength" and "AllocatedSize" fields to zero, for each "InitialApicId".
> 
> It's a waste -- the memory is allocated only for ensuring that
> PiSmmCpuDxeSmm does not program any CPU registers during S3 resume.
> 
> Setting "AcpiCpuData->RegisterTable" and
> "AcpiCpuData->PreSmmInitRegisterTable" should have the same effect.

... sorry, I meant: setting "AcpiCpuData->RegisterTable" and
"AcpiCpuData->PreSmmInitRegisterTable" *TO NULL* should have the same
effect.

Thanks,
Laszlo

> 
> 
> (3) The same simplification should be then mirrored to
> "OvmfPkg/CpuS3DataDxe/CpuS3Data.c".
> 
> I can write the OvmfPkg patch myself, of course, but first I'd like to
> see this use case confirmed / supported.
> 
> This patch looks OK otherwise.
> 
> Thanks!
> Laszlo
> 
> 
> 
> 
> 
>