linux-kernel - Re: [PATCH 01/11] x86/mm: factor out pageattr _PAGE

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Message-ID: <CA+55aFw7mLJrr+VqvEY-T3KqR2-xaYSoyU2Jg7VY1Sb1cu1L-w@mail.gmail.com>
Date:   Mon, 2 Apr 2018 10:52:34 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jürgen Groß <jgross@...e.com>,
        "the arch/x86 maintainers" <x86@...nel.org>, namit@...are.com
Subject: Re: [PATCH 01/11] x86/mm: factor out pageattr _PAGE_GLOBAL setting

On Mon, Apr 2, 2018 at 10:27 AM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> Aside: _PAGE_GLOBAL is ignored when CR4.PGE=1, so why do we
> even go to the trouble of filtering it anywhere?

I'm assuming this is a typo, and you mean "when CR4.PGE=0".

The question you raise may be valid, but within the particular context
of *this* patch it is not.

In the context of this particular patch, the issue is that we use
_PAGE_GLOBAL as _PAGE_BIT_PROTNONE when the present bit isn't set.

       Linus