linux-kernel - Re: [patch V4 part 3 04/29] x86/traps: Make interrupt enable/disable symmetric in C code

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Message-ID: <4b13ee35-da6f-a77d-cb19-1b32657cb939@oracle.com>
Date:   Thu, 7 May 2020 17:25:56 +0200
From:   Alexandre Chartre <alexandre.chartre@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>
Subject: Re: [patch V4 part 3 04/29] x86/traps: Make interrupt enable/disable
 symmetric in C code


On 5/5/20 3:43 PM, Thomas Gleixner wrote:
> Traps enable interrupts conditionally but rely on the ASM return code to
> disable them again. That results in redundant interrupt disable and trace
> calls.
> 
> Make the trap handlers disable interrupts before returning to avoid that,
> which allows simplification of the ASM entry code.
> 
> Originally-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> ---
>   arch/x86/kernel/traps.c |   28 +++++++++++++++++++---------
>   arch/x86/mm/fault.c     |   15 +++++++++++++--
>   2 files changed, 32 insertions(+), 11 deletions(-)
> 

So this patch makes C trap handlers disable interrupts on return but there's no
change to the ASM entry code, which will still (also) disable interrupts. I suppose
this is cleaned up in a next patch. So it's worth mentioning that the "simplification
of the ASM entry code" is not in this patch.

alex.