Re: [PATCH 2/2] x86/mm: Introduce 'no5lvl' kernel parameter

[Thomas Gleixner]

On Fri, 11 May 2018, Kirill A. Shutemov wrote:
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1008,6 +1008,12 @@ static void __init early_identify_cpu(struct 
> cpuinfo_x86 *c)
>        */
>       setup_clear_cpu_cap(X86_FEATURE_PCID);
>  #endif
> +
> +#ifdef CONFIG_X86_5LEVEL
> +     /* Clear the 5-level paging feature if user asked for 'no5lvl' */

no5lvl is only one reason why 5 level paging is not available.

> +     if (!__pgtable_l5_enabled)
> +             setup_clear_cpu_cap(X86_FEATURE_LA57);
> +#endif

And that #ifdeffery can be avoided by simply doing:

        if (IS_ENABLED(CONFIG_X86_5LEVEL) && !pgtable_l5_enabled)
                setup_clear_cpu_cap(X86_FEATURE_LA57);

Hmm?

Thanks,

        tglx