MdePkg/Library/BaseLib/Ia32/WriteMsr64.c

   1 /** @file
   2   AsmWriteMsr64 function
   3
   4   Copyright (c) 2006 - 2021, Intel Corporation. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 #include <Library/RegisterFilterLib.h>
  10
  11 /**
  12   Writes a 64-bit value to a Machine Specific Register(MSR), and returns the
  13   value.
  14
  15   Writes the 64-bit value specified by Value to the MSR specified by Index. The
  16   64-bit value written to the MSR is returned. No parameter checking is
  17   performed on Index or Value, and some of these may cause CPU exceptions. The
  18   caller must either guarantee that Index and Value are valid, or the caller
  19   must establish proper exception handlers. This function is only available on
  20   IA-32 and x64.
  21
  22   @param  Index The 32-bit MSR index to write.
  23   @param  Value The 64-bit value to write to the MSR.
  24
  25   @return Value
  26
  27 **/
  28 UINT64
  29 EFIAPI
  30 AsmWriteMsr64 (
  31   IN UINT32  Index,
  32   IN UINT64  Value
  33   )
  34 {
  35   BOOLEAN  Flag;
  36
  37   Flag = FilterBeforeMsrWrite (Index, &Value);
  38   if (Flag) {
  39     _asm {
  40       mov     edx, dword ptr [Value + 4]
  41       mov     eax, dword ptr [Value + 0]
  42       mov     ecx, Index
  43       wrmsr
  44     }
  45   }
  46
  47   FilterAfterMsrWrite (Index, &Value);
  48
  49   return Value;
  50 }