Re: [PATCH 14/29] x86/ibt: Add IBT feature, MSR and #CP handling

[Edgecombe, Rick P]

On Fri, 2022-02-18 at 17:49 +0100, Peter Zijlstra wrote:
> +       cr4_set_bits(X86_CR4_CET);
> +
> +       rdmsrl(MSR_IA32_S_CET, msr);
> +       if (cpu_feature_enabled(X86_FEATURE_IBT))
> +               msr |= CET_ENDBR_EN;
> +       wrmsrl(MSR_IA32_S_CET, msr);

So I guess implicit in all of this is that MSR_IA32_S_CET will not be
managed by xsaves (makes sense).

But it still might be good to add the supervisor cet xfeature number to
XFEATURE_MASK_SUPERVISOR_UNSUPPORTED, with analogous reasoning to
XFEATURE_MASK_PT.