linux-kernel - Re: [tip:x86/mm] x86/boot/compressed/64: Describe the logic behind the LA57 check

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Message-ID: <20180312174120.wtopp54bskk5a5fu@gmail.com>
Date:   Mon, 12 Mar 2018 18:41:20 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Peter Zijlstra <peterz@...radead.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Anvin <hpa@...or.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jürgen Groß <jgross@...e.com>,
        linux-tip-commits@...r.kernel.org,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [tip:x86/mm] x86/boot/compressed/64: Describe the logic behind
 the LA57 check


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> But regardless, I think we're better off with a "wait and see" approach.
> 
> IOW, try to use 5-level whenever possible for now, and _if_ somebody actually 
> can show that 4-level page tables perform better or have some other advantage, 
> we can then try to be clever later when it's all tested and it's just an 
> optimization, not a "that code won't even run normally and gets basically zero 
> coverage".

Ok, fair enough - and the testing argument makes sense as well.

Thanks,

	Ingo