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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Alexandre Chartre <alexandre.chartre@oracle.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     x86@kernel.org, "Paul E. McKenney" <paulmck@kernel.org>,
        Andy Lutomirski <luto@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Petr Mladek <pmladek@suse.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Juergen Gross <jgross@suse.com>,
        Brian Gerst <brgerst@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Will Deacon <will@kernel.org>
Subject: Re: [patch V4 part 3 04/29] x86/traps: Make interrupt enable/disable symmetric in C code
In-Reply-To: <4b13ee35-da6f-a77d-cb19-1b32657cb939@oracle.com>
References: <20200505134354.774943181@linutronix.de> <20200505134903.622702796@linutronix.de> <4b13ee35-da6f-a77d-cb19-1b32657cb939@oracle.com>
Date:   Thu, 07 May 2020 19:14:00 +0200
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Alexandre Chartre <alexandre.chartre@oracle.com> writes:

> 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@infradead.org>
>> Signed-off-by: Thomas Gleixner <tglx@linutronix.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.

I thought that was expressed by:

>> which allows simplification of the ASM entry code.

but yeah it's ambigous. Will clarify.

Thanks,

        tglx