linux-kernel - Re: [RFC, PATCHv1 15/28] x86: detect 5-level paging support

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Date:   Thu, 15 Dec 2016 12:57:43 -0800
From:   hpa@...or.com
To:     Andi Kleen <ak@...ux.intel.com>, Borislav Petkov <bp@...en8.de>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCHv1 15/28] x86: detect 5-level paging support

On December 15, 2016 11:20:17 AM PST, Andi Kleen <ak@...ux.intel.com> wrote:
>
>The code is not calling CPUID in any performance critical path, only
>at initialization. So any discussion about saving a few instructions
>is a complete waste of time.
>
>-Andi

NB: the chief offender is Loadlin, which is still used in some manufacturing flows that depends on a mix of legacy DOS and Linux applications; however, older versions of LILO also have this problem.
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