linux-kernel - Re: [RESEND][patch V3 06/23] bug: Annotate WARN/BUG/stackfail as noinstr safe

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Message-ID: <20200402213431.GK2452@worktop.programming.kicks-ass.net>
Date:   Thu, 2 Apr 2020 23:34:31 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Paul McKenney <paulmck@...nel.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Brian Gerst <brgerst@...il.com>,
        Juergen Gross <jgross@...e.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Subject: Re: [RESEND][patch V3 06/23] bug: Annotate WARN/BUG/stackfail as
 noinstr safe

On Thu, Apr 02, 2020 at 04:01:15PM -0500, Josh Poimboeuf wrote:
> On Fri, Mar 20, 2020 at 07:00:02PM +0100, Thomas Gleixner wrote:
> > Warnings, bugs and stack protection fails from noinstr sections, e.g. low
> > level and early entry code, are likely to be fatal.
> > 
> > Mark them as "safe" to be invoked from noinstr protected code to avoid
> > annotating all usage sites. Getting the information out is important.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > ---
> >  arch/x86/include/asm/bug.h |    3 +++
> >  include/asm-generic/bug.h  |    9 +++++++--
> >  kernel/panic.c             |    4 +++-
> >  3 files changed, 13 insertions(+), 3 deletions(-)
> > 
> > --- a/arch/x86/include/asm/bug.h
> > +++ b/arch/x86/include/asm/bug.h
> > @@ -70,13 +70,16 @@ do {									\
> >  #define HAVE_ARCH_BUG
> >  #define BUG()							\
> >  do {								\
> > +	instr_begin();						\
> >  	_BUG_FLAGS(ASM_UD2, 0);					\
> >  	unreachable();						\
> >  } while (0)
> 
> For visual symmetry at least, it seems like this wants an instr_end()
> before the unreachable().  Does objtool not like that?

Can't remember, but I think it's weird to put something after you know
it unreachable.