linux-kernel - Re: [patch V4 part 3 10/29] x86/idtentry: Provide macros to define/declare IDT entry points

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Message-ID: <87blmu4uya.fsf@nanos.tec.linutronix.de>
Date:   Mon, 11 May 2020 12:39:09 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        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 10/29] x86/idtentry: Provide macros to define/declare IDT entry points

Andy Lutomirski <luto@...nel.org> writes:
> On Tue, May 5, 2020 at 7:15 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>>
>> Provide DECLARE/DEFINE_IDTENTRY() macros.
>
> Acked-by: Andy Lutomirski <luto@...nel.org>
>
> except:
>
>>
>> DEFINE_IDTENTRY() provides a wrapper which acts as the function
>> definition. The exception handler body is just appended to it with curly
>> brackets. The entry point is marked notrace/noprobe so that irq tracing and
>> the enter_from_user_mode() can be moved into the C-entry point.
>
> "noinstr", perhaps?  I'm guessing you write this text before noinstr
> happened.

Yes.

> Also, would it perhaps make sense in the future to include the
> idtentry macro somehow (via inline asm or gcc options) so that
> DEFINE_IDTENTRY() could emit the stub instead of leaving it to
> DECLARE_IDTENTRY()?  It might end up too messy in practice, I suppose.
> This is obviously not worth changing right now, but maybe down the
> road.

Maybe. Right now my entry/rcu/tracing induced brainmelt is far too
advanced to try thinking about it :)