linux-kernel - Re: [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits

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Date:   Fri, 26 Jan 2018 19:49:15 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     x86-ml <x86@...nel.org>, linux-tip-commits@...r.kernel.org,
        hpa@...or.com, gregkh@...uxfoundation.org, tglx@...utronix.de,
        thomas.lendacky@....com, linux-kernel@...r.kernel.org,
        mingo@...nel.org
Subject: Re: [PATCH] x86/cpufeatures: Cleanup AMD speculation feature bits

On Fri, Jan 26, 2018 at 06:45:18PM +0000, David Woodhouse wrote:
> On Fri, 2018-01-26 at 19:41 +0100, Borislav Petkov wrote:
> > +#define X86_FEATURE_AMD_IBPB           (13*32+12) /* "" Indirect Branch Prediction Barrier MSR */
> 
> Stray quotes.

No no, those quotes are magical. :)

They don't show the string in /proc/cpuinfo, see arch/x86/kernel/cpu/mkcapflags.sh

> > +#define X86_FEATURE_IBRS               (13*32+14) /* Indirect Branch Restricted Speculation */
> 
> Please don't call it that. Call it X86_FEATURE_AMD_IBRS and leave
> X86_FEATURE_IBRS to parallel X86_FEATURE_IBPB as the *software* bit
> which is vendor-independent.

Do we have a X86_FEATURE_IBRS bit?

If so, then this bit should become

#define X86_FEATURE_AMD_IBRS      (13*32+14) /* "" Speculation Control MSR only (AMD) */

*with* the magic quotes.

-- 
Regards/Gruss,
    Boris.

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