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

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

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.


(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