Re: [PATCH 01/19] x86/cpufreatures: add AMD CPPC extension feature flag

Huang Rui
2021-09-13T09:49:04Z

Hi Boris,

On Fri, Sep 10, 2021 at 01:58:19AM +0800, Borislav Petkov wrote:
> On Wed, Sep 08, 2021 at 10:59:43PM +0800, Huang Rui wrote:
> > Add Collaborative Processor Performance Control Extension feature flag
> > for AMD processors.
> >
> > Signed-off-by: Huang Rui <ray.huang@amd.com>
> > ---
> > arch/x86/include/asm/cpufeatures.h | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index d0ce5cfd3ac1..f7aea50e3371 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -313,6 +313,7 @@
> > #define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
> > #define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative Store Bypass Disable */
> > #define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store Bypass is fixed in hardware. */
> > +#define X86_FEATURE_AMD_CPPC_EXT (13*32+27) /* Collaborative Processor Performance Control Extension */
>
> Why not simply X86_FEATURE_AMD_CPPC ?

This feature flag indicates the full MSR hardware solution of AMD P-States,
if it is not set, that means we will go with in shared memory hardware
solution. So we name this as extension. I will explain the details in the
commit log at V2. ;-)

Thanks,
Ray