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SubjectRe: [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@amazon.co.uk>
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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


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