[edk2-devel] [PATCH V7 25/37] MdeModulePkg: EFER should not be changed in TDX

[Min Xu]

On March 3, 2022 11:12 AM, Wang Jian wrote:
> 
> Hi Min,
> 
> I think the PCD should not be dynamic. Dynamic PCD is used for those
> features which can be changed at boot time. But, for Intel processor, it
> should always stay as FALSE. So there's no need to make it dynamic.
> FixedAtBuild should be fine.
> 
I realize this PCD is not necessary. According to [TDX] Sec 10.1.5, IA32_EFER.NXE is initialized to 1. So in the function EnableExecuteDisableBit @ MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c, we can check if BIT11 is set before calling AsmWriteMsr64. It looks like:
VOID EnableExecuteDisableBit (  VOID )
{
  UINT64  MsrRegisters;

  MsrRegisters = AsmReadMsr64 (0xC0000080);
  if ((MsrRegisters & BIT11) == 0) {
    MsrRegisters |= BIT11;
    AsmWriteMsr64 (0xC0000080, MsrRegisters);
  }
}

[TDX] https://www.intel.com/content/dam/develop/external/us/en/documents/tdx-module-1.0-public-spec-v0.931.pdf

Thanks
Min


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