Re: [PATCH] UefiCpuPkg/MpInitLib: Skip reading PlatformId on AMD processors.

["Laszlo Ersek" <lersek@redhat.com>]

On 02/28/20 19:58, Leo Duran wrote:
> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2556
> 
> This patch uses CPUID signature check to skip reading the PlatformId MSR,
> which is not implemented on AMD processors.
> 
> The PlatformId is used for loading microcode patches, which is also not
> supported and AMD-based platforms. To mitigate the PlatformId dependency,
> PcdCpuMicrocodePatchAddress and PcdCpuMicrodePatchRegionSize must be set
> to 0 (default value), in order to bypass microcode loading code paths.
> 
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Signed-off-by: Leo Duran <leo.duran@amd.com>
> ---
>  UefiCpuPkg/Library/MpInitLib/MpLib.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/MpInitLib/MpLib.c b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> index d0fbc17..d2200c3 100644
> --- a/UefiCpuPkg/Library/MpInitLib/MpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/MpLib.c
> @@ -2,6 +2,8 @@
>    CPU MP Initialize Library common functions.
>  
>    Copyright (c) 2016 - 2020, Intel Corporation. All rights reserved.<BR>
> +  Copyright (c) 2020, AMD Inc. All rights reserved.<BR>
> +
>    SPDX-License-Identifier: BSD-2-Clause-Patent
>  
>  **/
> @@ -10,6 +12,29 @@
>  
>  EFI_GUID mCpuInitMpLibHobGuid = CPU_INIT_MP_LIB_HOB_GUID;
>  
> +
> +/**
> +  Determine if the standard CPU signature is "AuthenticAMD".
> +
> +  @retval TRUE  The CPU signature matches.
> +  @retval FALSE The CPU signature does not match.
> +
> +**/
> +BOOLEAN
> +StandardSignatureIsAuthenticAMD (
> +  VOID
> +  )
> +{
> +  UINT32  RegEbx;
> +  UINT32  RegEcx;
> +  UINT32  RegEdx;
> +
> +  AsmCpuid (CPUID_SIGNATURE, NULL, &RegEbx, &RegEcx, &RegEdx);
> +  return (RegEbx == CPUID_SIGNATURE_AUTHENTIC_AMD_EBX &&
> +          RegEcx == CPUID_SIGNATURE_AUTHENTIC_AMD_ECX &&
> +          RegEdx == CPUID_SIGNATURE_AUTHENTIC_AMD_EDX);
> +}
> +
>  /**
>    The function will check if BSP Execute Disable is enabled.
>  
> @@ -564,8 +589,13 @@ InitializeApData (
>    CpuMpData->CpuData[ProcessorNumber].Waiting    = FALSE;
>    CpuMpData->CpuData[ProcessorNumber].CpuHealthy = (BistData == 0) ? TRUE : FALSE;
>  
> -  PlatformIdMsr.Uint64 = AsmReadMsr64 (MSR_IA32_PLATFORM_ID);
> -  CpuMpData->CpuData[ProcessorNumber].PlatformId = (UINT8) PlatformIdMsr.Bits.PlatformId;
> +  //
> +  // NOTE: PlatformId is not relevant on AMD platforms.
> +  //
> +  if (!StandardSignatureIsAuthenticAMD ()) {
> +    PlatformIdMsr.Uint64 = AsmReadMsr64 (MSR_IA32_PLATFORM_ID);
> +    CpuMpData->CpuData[ProcessorNumber].PlatformId = (UINT8)PlatformIdMsr.Bits.PlatformId;
> +  }
>  
>    AsmCpuid (
>      CPUID_VERSION_INFO,
> 

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