On Fri, 2018-02-16 at 11:17 -0800, Dave Hansen wrote:
> +static bool cpu_has_rsb_override(void)
> +{
> +       u64 ia32_cap = 0;
> +
> +        if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
> +               rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> +
> +        /* RSBO == RSB Override */
> +        if (ia32_cap & ARCH_CAP_RSBO)
> +               return true;

That would be the third such construct. As some point we should
probably put the bits of MSR_IA32_ARCH_CAPABILITIES into cpufeatures a
bit like the 'scattered' CPUID bits.