Re: [PATCH 29/35] x86/speculation: Add IPBP support

[Borislav Petkov]

On Thu, Jan 18, 2018 at 12:35:23PM -0600, Josh Poimboeuf wrote:
> Maybe I missed the memo, why do we need both X86_FEATURE_IBPB and
> X86_FEATURE_AMD_IBPB?

So AMD_IBPB is a different CPUID bit in a different CPUID function
and on Intel, IBPB is set only when X86_FEATURE_SPEC_CTRL - see
specctrl_init_ibpb() in that same patch.

IOW, CPUID(7).EDAC[26] means both IBRS and IBPB on Intel.

So, in the end of the day, X86_FEATURE_IBPB is the feature bit we'll be
testing and X86_FEATURE_AMD_IBPB is used only to set X86_FEATURE_IBPB.

:-)

More confused?

-- 
Regards/Gruss,
    Boris.

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