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.
-- 
2.21.0.windows.1


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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

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