linux-kernel - Re: [PATCH 04/23] x86, tlb: make CR4-based TLB flushes more robust

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Message-ID: <CALCETrW06XjaWYD1O_HPXPDrHS96FZz9=OkPCQ3vsKrAxnr8+A@mail.gmail.com>
Date:   Wed, 1 Nov 2017 01:01:45 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at, daniel.gruss@...k.tugraz.at,
        michael.schwarz@...k.tugraz.at,
        Andrew Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 04/23] x86, tlb: make CR4-based TLB flushes more robust

On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> Our CR4-based TLB flush currently requries global pages to be
> supported *and* enabled.  But, we really only need for them to be
> supported.  Make the code more robust by alllowing X86_CR4_PGE to
> clear as well as set.
>
> This change was suggested by Kirill Shutemov.

I may have missed something, but why would be ever have CR4.PGE off?