linux-kernel - Re: [RFC PATCH for 4.18 3/5] rseq: uapi: declare rseq

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Date:   Fri, 6 Jul 2018 15:38:51 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Dave Watson <davejwatson@...com>, Paul Turner <pjt@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Russell King <linux@....linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
        Chris Lameter <cl@...ux.com>, Ben Maurer <bmaurer@...com>,
        rostedt <rostedt@...dmis.org>,
        Josh Triplett <josh@...htriplett.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [RFC PATCH for 4.18 3/5] rseq: uapi: declare rseq_cs field as
 union, update includes

----- On Jul 6, 2018, at 3:35 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- On Jul 6, 2018, at 3:31 PM, Linus Torvalds torvalds@...ux-foundation.org
> wrote:
> 
>> On Fri, Jul 6, 2018 at 12:23 PM Mathieu Desnoyers
>> <mathieu.desnoyers@...icios.com> wrote:
>>>
>>> For -rc, I would favor the following simpler approach. Or I could even
>>> just use get_user() instead. Thoughts ?
>> 
>> Please just use "get_user()".
>> 
>> In fact, we should be thinking seriosly about just removing
>> __get_user() entirely. It's wrong. It optimizes the wrong thing
>> entirely. It _used_ to be that the range check was noticeable, and it
>> really isn't any more. These days the expensive parts are the SMAP
>> costs, and both get_user() and __get_user() have those, except
>> get_user() is safer and doesn't waste I$ on inlining the code to
>> disable and re-enable SMAP.
> 
> Will do, thanks!

Should I change all 4 bytes __get_user()/__put_user() in kernel/rseq.c
for get_user()/put_user() to ensure consistency ?

Thanks,

Mathieu

> 
> Mathieu
> 
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com