Re: [edk2-devel] [PATCH] UefiCpuPkg CpuCommonFeaturesLib: Remove CPU generation check

["Zeng, Star" <star.zeng@intel.com>]

Laszlo,

> -----Original Message-----
> From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of
> Laszlo Ersek
> Sent: Thursday, May 16, 2019 9:06 PM
> To: Zeng, Star <star.zeng@intel.com>; devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Kumar,
> Chandana C <chandana.c.kumar@intel.com>
> Subject: Re: [edk2-devel] [PATCH] UefiCpuPkg CpuCommonFeaturesLib:
> Remove CPU generation check
> 
> 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.

That is the case we met. The purpose of this patch is to make the code more usable.

> 
> 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

Yes, right.

Let me show some examples for the generations not in the list above.

1. MSR 0x13C is available: our some internal generations are in this case.
Without the patch, code needs to use function level override method in a CpuSpecificFeaturesLib.
    Status = RegisterCpuFeature (
               "AESNI",
               NULL,                                         // Use core function
               SpecificAesniSupport,                         // Override core function
               NULL,                                         // Use core function
               CPU_FEATURE_AESNI,
               CPU_FEATURE_END
               );
With the patch, the function level override will be not needed. The benefit of this patch is here.

2. MSR 0x13C is not available: let's assume some other MSR will be available for the case.
Without or with the patch, codes both need to use function level override method in a CpuSpecificFeaturesLib.
    Status = RegisterCpuFeature (
               "AESNI",
               NULL,                                         // Use core function
               SpecificAesniSupport,                         // Override core function
               SpecificAesniInitialize,                         // Override core function
               CPU_FEATURE_AESNI,
               CPU_FEATURE_END
               );


Thanks,
Star

> 
> 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
> 
>