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

["Ni, Ray" <ray.ni@intel.com>]

Star,
I think the discussion is about providing the evidence to support removing the generation check.
Not just the benefit of that.

Thanks,
Ray

> -----Original Message-----
> From: Zeng, Star
> Sent: Thursday, May 16, 2019 10:52 PM
> To: devel@edk2.groups.io; lersek@redhat.com
> Cc: Dong, Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Kumar,
> Chandana C <chandana.c.kumar@intel.com>; Zeng, Star
> <star.zeng@intel.com>
> Subject: RE: [edk2-devel] [PATCH] UefiCpuPkg CpuCommonFeaturesLib:
> Remove CPU generation check
> 
> 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
> >
> >