linux-kernel - Re: [patch V4 part 4 07/24] x86/traps: Split int3 handler up

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Date:   Thu, 14 May 2020 11:39:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        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>
Subject: Re: [patch V4 part 4 07/24] x86/traps: Split int3 handler up

On Wed, May 13, 2020 at 10:03:13PM -0700, Andy Lutomirski wrote:
> On Tue, May 5, 2020 at 7:16 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > For code simplicity split up the int3 handler into a kernel and user part
> > which makes the code flow simpler to understand.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  arch/x86/kernel/traps.c |   67 +++++++++++++++++++++++++++---------------------
> >  1 file changed, 39 insertions(+), 28 deletions(-)
> >
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -564,6 +564,35 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_pr
> >         cond_local_irq_disable(regs);
> >  }
> >
> > +static bool do_int3(struct pt_regs *regs)
> > +{
> > +       int res;
> > +
> > +#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
> > +       if (kgdb_ll_trap(DIE_INT3, "int3", regs, 0, X86_TRAP_BP,
> > +                        SIGTRAP) == NOTIFY_STOP)
> > +               return true;
> > +#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
> > +
> > +#ifdef CONFIG_KPROBES
> > +       if (kprobe_int3_handler(regs))
> > +               return true;
> > +#endif
> > +       res = notify_die(DIE_INT3, "int3", regs, 0, X86_TRAP_BP, SIGTRAP);
> > +
> > +       return res == NOTIFY_STOP;
> > +}
> > +
> > +static void do_int3_user(struct pt_regs *regs)
> > +{
> > +       if (do_int3(regs))
> > +               return;
> > +
> > +       cond_local_irq_enable(regs);
> > +       do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, 0, 0, NULL);
> > +       cond_local_irq_disable(regs);
> > +}
> > +
> >  DEFINE_IDTENTRY_RAW(exc_int3)
> >  {
> >         /*
> > @@ -581,37 +610,19 @@ DEFINE_IDTENTRY_RAW(exc_int3)
> >          * because the INT3 could have been hit in any context including
> >          * NMI.
> >          */
> > +       if (user_mode(regs)) {
> >                 idtentry_enter(regs);
> > +               instr_begin();
> > +               do_int3_user(regs);
> > +               instr_end();
> >                 idtentry_exit(regs);
> > +       } else {
> > +               nmi_enter();
> > +               instr_begin();
> > +               do_int3(regs);
> 
> I think you should be checking the return value here.  Presumably this
> should die() if it's not handled, since otherwise it will just
> infinite loop.

Indeed. Thanks!

> > +               instr_end();
> >                 nmi_exit();
> > +       }
> >  }
> >
> >  #ifdef CONFIG_X86_64
> >