linux-kernel - Re: [PATCH 00/35 v5] PTI support for x32

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Message-ID: <CA+55aFzrYbTMXyZBVqRV875HwQJNxD+822RGeeDb7BLDLU8aWA@mail.gmail.com>
Date:   Mon, 16 Apr 2018 09:13:22 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Joerg Roedel <joro@...tes.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>, Jiri Kosina <jkosina@...e.cz>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Brian Gerst <brgerst@...il.com>,
        David Laight <David.Laight@...lab.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Eduardo Valentin <eduval@...zon.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Will Deacon <will.deacon@....com>,
        "Liguori, Anthony" <aliguori@...zon.com>,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        Hugh Dickins <hughd@...gle.com>,
        Kees Cook <keescook@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <llong@...hat.com>, Pavel Machek <pavel@....cz>,
        "David H . Gutteridge" <dhgutteridge@...patico.ca>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 00/35 v5] PTI support for x32

On Mon, Apr 16, 2018 at 9:01 AM, Joerg Roedel <joro@...tes.org> wrote:
>
> Okay, I verify if there are any global bits left in the page-tables.
> According to the PTDUMP_X86 the cpu_entry_area is mapped with G=1 (which
> should be fine?) and another 4M range in the kernel mapping. I need to
> check what that is.

All the kernel entry code that is both in the user mapping and the
kernel mapping should be marked G.

We had missed a lot of it (and the impact is very small with PCID),
but if you rebased on top of 4.17-rc1 you should have it fixed at
least on 64-bit.

See for example commit 8c06c7740d19 ("x86/pti: Leave kernel text
global for !PCID") and in particular the performance numbers (that's
an Atom microserver, but it was chosen due to lack of PCID).

                  Linus