linux-kernel - Re: [PATCH v5 3/7] x86/cpufeatures: Add AMD feature bits for Speculation Control

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Date:   Thu, 25 Jan 2018 22:37:30 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     David Woodhouse <dwmw@...zon.co.uk>,
        Tom Lendacky <thomas.lendacky@....com>, arjan@...ux.intel.com,
        karahmed@...zon.de, x86@...nel.org, linux-kernel@...r.kernel.org,
        tim.c.chen@...ux.intel.com, peterz@...radead.org,
        pbonzini@...hat.com, ak@...ux.intel.com,
        torvalds@...ux-foundation.org, gregkh@...ux-foundation.org,
        dave.hansen@...el.com, gnomes@...rguk.ukuu.org.uk,
        ashok.raj@...el.com, mingo@...nel.org
Subject: Re: [PATCH v5 3/7] x86/cpufeatures: Add AMD feature bits for
 Speculation Control

On Thu, 25 Jan 2018, Borislav Petkov wrote:

> + Tom.
> 
> On Thu, Jan 25, 2018 at 04:14:11PM +0000, David Woodhouse wrote:
> > AMD exposes the PRED_CMD/SPEC_CTRL MSRs slightly differently to Intel.
> > See http://lkml.kernel.org/r/2b3e25cc-286d-8bd0-aeaf-9ac4aae39de8@amd.com
> > 
> > Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > ---
> >  arch/x86/include/asm/cpufeatures.h | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index 0a51070..ae3212f 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -269,6 +269,9 @@
> >  #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
> >  #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
> >  #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
> > +#define X86_FEATURE_AMD_PRED_CMD	(13*32+12) /* Prediction Command MSR (AMD) */
> > +#define X86_FEATURE_AMD_SPEC_CTRL	(13*32+14) /* Speculation Control MSR only (AMD) */
> > +#define X86_FEATURE_AMD_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors (AMD) */
> 
> So this leaf is AMD-specific so you can drop the AMD strings above.
> Also, let's simplify this as those flags appear in /proc/cpuinfo:
> 
> #define X86_FEATURE_IBPB		(13*32+12) /* Indirect Branch Prediction Barrier: Prediction Command MSR */
> #define X86_FEATURE_IBRS		(13*32+14) /* Speculation Control MSR only */
> #define X86_FEATURE_STIBP		(13*32+15) /* Single Thread Indirect Branch Predictors */
> 
> so that we have "ibpb", "ibrs" and "stibp" respectively.

That wont work as the intel bits are at a different leave and we cant
define the same thing twice....

Thanks,

	tglx