Re: [PATCH] UefiCpuPkg CpuCommonFeaturesLib: Remove CPU generation check

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

Hi Star,

On 05/16/19 12:33, Star Zeng wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1679
> 
> The checking to CpuInfo->CpuIdVersionInfoEcx.Bits.AESNI is enough,
> the checking to CPU generation could be removed, then the code
> could be reused by more platforms.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Eric Dong <eric.dong@intel.com>
> Cc: Ruiyu Ni <ruiyu.ni@intel.com>
> Cc: Chandana Kumar <chandana.c.kumar@intel.com>
> Signed-off-by: Star Zeng <star.zeng@intel.com>
> ---
>  UefiCpuPkg/Library/CpuCommonFeaturesLib/Aesni.c | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/CpuCommonFeaturesLib/Aesni.c b/UefiCpuPkg/Library/CpuCommonFeaturesLib/Aesni.c
> index b79446ba3ca9..4a56eec1b267 100644
> --- a/UefiCpuPkg/Library/CpuCommonFeaturesLib/Aesni.c
> +++ b/UefiCpuPkg/Library/CpuCommonFeaturesLib/Aesni.c
> @@ -57,15 +57,9 @@ AesniSupport (
>    MSR_SANDY_BRIDGE_FEATURE_CONFIG_REGISTER   *MsrFeatureConfig;
>  
>    if (CpuInfo->CpuIdVersionInfoEcx.Bits.AESNI == 1) {
> -    if (IS_SANDY_BRIDGE_PROCESSOR (CpuInfo->DisplayFamily, CpuInfo->DisplayModel) ||
> -        IS_SILVERMONT_PROCESSOR (CpuInfo->DisplayFamily, CpuInfo->DisplayModel) ||
> -        IS_XEON_5600_PROCESSOR (CpuInfo->DisplayFamily, CpuInfo->DisplayModel) ||
> -        IS_XEON_E7_PROCESSOR (CpuInfo->DisplayFamily, CpuInfo->DisplayModel) ||
> -        IS_XEON_PHI_PROCESSOR (CpuInfo->DisplayFamily, CpuInfo->DisplayModel)) {
> -      MsrFeatureConfig = (MSR_SANDY_BRIDGE_FEATURE_CONFIG_REGISTER *) ConfigData;
> -      ASSERT (MsrFeatureConfig != NULL);
> -      MsrFeatureConfig[ProcessorNumber].Uint64 = AsmReadMsr64 (MSR_SANDY_BRIDGE_FEATURE_CONFIG);
> -    }
> +    MsrFeatureConfig = (MSR_SANDY_BRIDGE_FEATURE_CONFIG_REGISTER *) ConfigData;
> +    ASSERT (MsrFeatureConfig != NULL);
> +    MsrFeatureConfig[ProcessorNumber].Uint64 = AsmReadMsr64 (MSR_SANDY_BRIDGE_FEATURE_CONFIG);
>      return TRUE;
>    }
>    return FALSE;
> 

the patch and the bugzilla ticket claim that the AESNI bit's presence in
CPUID guarantees that MSR 0x13C is available.

I don't see what guarantees this. According to the latest Intel SDM Vol
4, which I just downloaded (335592-069US, January 2019),
MSR_FEATURE_CONFIG is available on the following (DisplayFamily,
DisplayModel) pairs:

- 06_37H, 06_4AH, 06_4DH, 06_5AH, 06_5DH, 06_5CH, 06_7AH
- 06_25H, 06_2CH
- 06_2FH
- 06_2AH, 06_2DH
- 06_57H

Which seems to indicate that at least *the approach* of the original
code -- i.e. the family/model checking -- is correct. (It's possible
that the family/model list has to be extended from time to time, of course.)

Anyway, I don't intend to block this patch; OVMF does not use
CpuCommonFeaturesLib, so this change cannot regress it. I will let other
UefiCpuPkg reviewers decide about this patch.

Thanks!
Laszlo