Re: [PATCH 38/39] x86/mm/pti: Add Warning when booting on a PCID capable CPU

[Andy Lutomirski]

On Wed, Jul 11, 2018 at 4:29 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:
> From: Joerg Roedel <jroedel@xxxxxxx>
>
> Warn the user in case the performance can be significantly
> improved by switching to a 64-bit kernel.

...

> +#ifdef CONFIG_X86_32
> +       if (boot_cpu_has(X86_FEATURE_PCID)) {

I'm a bit confused. Wouldn't the setup_clear_cpu_cap() call in
early_identify_cpu() prevent this from working?

Boris, do we have a straightforward way to ask "does the CPU advertise
this feature in CPUID regardless of whether we have it enabled right
now"?

--Andy