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Subject: Re: [Patch v2 3/6] UefiCpuPkg/PiSmmCpuDxeSmm: Supports test then write new value logic.
To: Eric Dong <eric.dong@intel.com>, devel@edk2.groups.io
Cc: Ray Ni <ray.ni@intel.com>
References: <20190812103152.35164-1-eric.dong@intel.com>
 <20190812103152.35164-4-eric.dong@intel.com>
From: "Laszlo Ersek" <lersek@redhat.com>
Message-ID: <26c00f3a-dbf4-0f33-0a36-7c9700516f77@redhat.com>
Date: Mon, 12 Aug 2019 16:13:46 +0200
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On 08/12/19 12:31, Eric Dong wrote:
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2040
> 
> Supports new logic which test current value before write new value.
> Only write new value when current value not same as new value.
> 
> Signed-off-by: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> ---
>  UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
> 
> diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
> index b20992d5ab..61541838e8 100644
> --- a/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
> +++ b/UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c
> @@ -241,6 +241,7 @@ ProgramProcessorRegister (
>    UINTN                     ValidThreadCount;
>    UINT32                    *ValidCoreCountPerPackage;
>    EFI_STATUS                Status;
> +  UINT64                    CurrentValue;
>  
>    //
>    // Traverse Register Table of this logical processor
> @@ -263,6 +264,16 @@ ProgramProcessorRegister (
>        if (EFI_ERROR (Status)) {
>          continue;
>        }
> +      if (RegisterTableEntry->TestThenWrite) {
> +        CurrentValue = BitFieldRead64 (
> +                         Value,
> +                         RegisterTableEntry->ValidBitStart,
> +                         RegisterTableEntry->ValidBitStart + RegisterTableEntry->ValidBitLength - 1
> +                         );
> +        if (CurrentValue == RegisterTableEntry->Value) {
> +          continue;
> +        }
> +      }
>        Value = (UINTN) BitFieldWrite64 (
>                          Value,
>                          RegisterTableEntry->ValidBitStart,
> @@ -275,6 +286,24 @@ ProgramProcessorRegister (
>      // The specified register is Model Specific Register
>      //
>      case Msr:
> +      if (RegisterTableEntry->TestThenWrite) {
> +        Value = (UINTN)AsmReadMsr64 (RegisterTableEntry->Index);
> +        if (RegisterTableEntry->ValidBitLength >= 64) {
> +          if (Value == RegisterTableEntry->Value) {
> +            continue;
> +          }
> +        } else {
> +          CurrentValue = BitFieldRead64 (
> +                           Value,
> +                           RegisterTableEntry->ValidBitStart,
> +                           RegisterTableEntry->ValidBitStart + RegisterTableEntry->ValidBitLength - 1
> +                           );
> +          if (CurrentValue == RegisterTableEntry->Value) {
> +            continue;
> +          }
> +        }
> +      }
> +
>        //
>        // If this function is called to restore register setting after INIT signal,
>        // there is no need to restore MSRs in register table.
> 

I assume that "RegisterTableEntry->Value" has all bits clear that fall
outside of the bitmask defined by ValidBitStart and ValidBitLength.

With that assumption:

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

Thanks
Laszlo