Re: [RFC PATCH v2 4/6] x86/boot: Set 5-level paging CPU cap before entering C code

[Ingo Molnar <mingo@kernel.org>]

* Ard Biesheuvel <ardb@kernel.org> wrote:

> > > -     if (IS_ENABLED(CONFIG_X86_5LEVEL) && (native_read_cr4() & X86_CR4_LA57))
> > > -             setup_force_cpu_cap(X86_FEATURE_5LEVEL_PAGING);
> 
> Note that at this point, we'll likely still have to force clear the 
> original X86_FEATURE_LA57 bit, to address the issue that Kirill 
> raised that user space is now likely to conflate the "la57" cpuinfo 
> string with 5-level paging being in use.

No, I think the general outcome of your series is fine and clean in 
terms of kernel-internal logic, and I wouldn't mess up that clarity 
with user ABI quirks: and we can solve the /proc/cpuinfo ABI 
compatibility requirement by exposing X86_FEATURE_5LEVEL_PAGING as 
'la57', and renaming X86_FEATURE_LA57 to X86_FEATURE_LA57_HW and 
exposing it as a (new) la57_hw flag, or so.

Thanks,

	Ingo