Trigger SMI to Do CpuIo Cause System Hangs Up Under Windows

We would like to use CpuIo protocol and must locate it first.

Status = gBS->LocateProtocol (&gEfiCpuIoProtocolGuid, NULL, &CpuIo);
There is a question here, system is entered windows that has exited boot service.
Therefore, we locate this protocol will cause system hangs up.
To avoid this, we should create a global variable to save the CpuIo pointer when system during POST phase.

EFI_CPU_IO_PROTOCOL   *mCpuIo = NULL;

EFI_DRIVER_ENTRY_POINT (SctCpuIoPointSave)
EFI_STATUS
SctCpuIoPointSave (
  IN EFI_HANDLE ImageHandle,
  IN EFI_SYSTEM_TABLE *SystemTable
  )
{
  EFI_STATUS Status;
  EFI_HANDLE Handle;
  DxeInitializeDriverLib (ImageHandle, SystemTable);

  //
  // Locate CpuIo protocol.
  //
  Status = gBS->LocateProtocol ( &gEfiCpuIoProtocolGuid, NULL, &mCpuIo ) ;
       
  return Status;
} // EnteyPoint.


Just need to call your function in SMI code to use CpuIo.
For example,

VOID
ShowPort80 (VOID)
{
  EFI_STATUS    Status ;
  UINT8                Data ;
  Data = 0x99;
  Status = mCpuIo->Io.Write (
                        mCpuIo,
                        EfiCpuIoWidthUint8,
                        0x80,
                        1,
                        &Data);
  ASSERT_EFI_ERROR (Status);
}