Re: [PATCH 3/3] x86/mm, tracing: Fix CR2 corruption

[Andy Lutomirski]

On Wed, Jul 3, 2019 at 3:01 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Wed, Jul 03, 2019 at 01:27:09PM -0700, Andy Lutomirski wrote:
> > On Wed, Jul 3, 2019 at 3:28 AM root <peterz@xxxxxxxxxxxxx> wrote:
>
> > > @@ -1338,18 +1347,9 @@ ENTRY(error_entry)
> > >         movq    %rax, %rsp                      /* switch stack */
> > >         ENCODE_FRAME_POINTER
> > >         pushq   %r12
> > > -
> > > -       /*
> > > -        * We need to tell lockdep that IRQs are off.  We can't do this until
> > > -        * we fix gsbase, and we should do it before enter_from_user_mode
> > > -        * (which can take locks).
> > > -        */
> > > -       TRACE_IRQS_OFF
> >
> > This hunk looks wrong.  Am I missing some other place that handles the
> > case where we enter from kernel mode and IRQs were on?
>
> > > -   CALL_enter_from_user_mode
> > >     ret
> > >
> > >  .Lerror_entry_done:
> > > -   TRACE_IRQS_OFF
> > >     ret
> > >
> > >     /*
>
> Did you perchance mean to complain about the .Lerror_entry_done one?

Yes, duh.

I would suggest compiling with DEBUG_LOCKDEP and running perf and the
x86 selftests.  IIRC that's what catches most of the IRQ flag tracing
errors.

>
> Because I'm not seeing how the one before CALL_enter_from_user_mode can
> ever be from-kernel.
>
> But yes, that .Lerror_entry_done one looks fishy.