linux-kernel - Re: [patch V6 36/37] x86/entry: Move paranoid irq tracing out of ASM code

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Message-ID: <CALCETrVCBMjEZmohRmJ0=F26LjYxyxP0L_x=c68ExGUampVk3g@mail.gmail.com>
Date:   Wed, 20 May 2020 10:13:02 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...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>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 36/37] x86/entry: Move paranoid irq tracing out of ASM code

On Wed, May 20, 2020 at 8:17 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Andy Lutomirski <luto@...nel.org> writes:
>
> > On Fri, May 15, 2020 at 5:11 PM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > I think something's missing here.  With this patch applied, don't we
> > get to exc_debug_kernel() -> handle_debug() without doing
> > idtentry_enter() or equivalent?  And that can even enable IRQs.
> >
> > Maybe exc_debug_kernel() should wrap handle_debug() in some
> > appropriate _enter() / _exit() pair?
>
> I'm the one who is missing something here, i.e. the connection of this
> patch to #DB. exc_debug_kernel() still looks like this:
>
>         nmi_enter_notrace();
>         handle_debug(regs, dr6, false);
>         nmi_exit_notrace();
>
> Confused.
>

Hmm.  I guess the code is correct-ish or at least as correct as it
ever was.  But $SUBJECT says "Move paranoid irq tracing out of ASM
code" but you didn't move it into all the users.  So now the NMI code
does trace_hardirqs_on_prepare() but the #DB code doesn't.  Perhaps
the changelog should mention this.

exc_kernel_debug() is an atrocity.  Every now and then I get started
on cleanup it up and so far I always get mired in the giant amount of
indirection.

So Acked-by: Andy Lutomirski <luto@...nel.org> if you write a credible
changelog.