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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 16 Apr 2018 09:13:22 -0700
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Subject: Re: [PATCH 00/35 v5] PTI support for x32
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
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        Dave Hansen <dave.hansen@intel.com>,
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        Borislav Petkov <bp@alien8.de>, Jiri Kosina <jkosina@suse.cz>,
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        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
        Denys Vlasenko <dvlasenk@redhat.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Greg KH <gregkh@linuxfoundation.org>,
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        Kees Cook <keescook@google.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        "David H . Gutteridge" <dhgutteridge@sympatico.ca>,
        Joerg Roedel <jroedel@suse.de>
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On Mon, Apr 16, 2018 at 9:01 AM, Joerg Roedel <joro@8bytes.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