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Date: Wed, 22 Mar 2017 13:21:38 -0700
From: "H. Peter Anvin" <>
To: Thomas Garnier <>
Cc: Andy Lutomirski <>, Ingo Molnar <>,
        Martin Schwidefsky <>,
        Heiko Carstens <>,
        David Howells <>, Arnd Bergmann <>,
        Al Viro <>, Dave Hansen <>,
        René Nyffenegger <>,
        Andrew Morton <>,
        Kees Cook
        "Paul E . McKenney" <>,
        Andy Lutomirski <>,
        Ard Biesheuvel
        Nicolas Pitre <>,
        Petr Mladek <>,
        Sebastian Andrzej Siewior <>,
        Sergey Senozhatsky <>,
        Helge Deller <>, Rik van Riel <>,
        John Stultz <>,
        Thomas Gleixner <>, Oleg Nesterov <>,
        Stephen Smalley <>,
        Pavel Tikhomirov <>,
        Frederic Weisbecker <>,
        Stanislav Kinsburskiy <>,
        Ingo Molnar <>, Paolo Bonzini <>,
        Dmitry Safonov <>,
        Borislav Petkov <>, Josh Poimboeuf <>,
        Brian Gerst <>, Jan Beulich <>,
        Christian Borntraeger <>,
        Fenghua Yu <>, He Chen <>,
        Russell King <>,
        Vladimir Murzin <>,
        Will Deacon
        Catalin Marinas <>,
        Mark Rutland <>, James Morse <>,
        "David A . Long" <>,
        Pratyush Anand <>, Laura Abbott <>,
        Andre Przywara <>,
        Chris Metcalf <>,
        linux-s390 <>,
        Linux API <>,
        the arch/x86 maintainers <>,
        Kernel Hardening <>
Subject: Re: [PATCH v3 2/4] x86/syscalls: Specific usage of

On 03/22/17 12:15, Thomas Garnier wrote:
> On Wed, Mar 15, 2017 at 10:43 AM, Thomas Garnier <> wrote:
>> Thanks for the feedback. I will look into inlining by default (looking
>> at code size on different arch), the updated patch for x86 in the
>> meantime:
> I did couple checks and it doesn't seem worth it. I will send a v4
> with the change below for additional feedback.

Can you specify what that means?

On x86, where there is only one caller of this, it really seems like it
ought to reduce the overhead to almost zero (since it most likely is
hidden in the pipeline.)

I would like to suggest defining it inline if
care about an architecture which doesn't have it.

Note that the upcoming 5-level paging (LA57) support will make
TASK_SIZE_MAX dependent on the CPU.  The best way to handle that is
probably to tag this immediate with an assembly alternative rather than
loading it from a memory variable (most likely taking a cache hit.)


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