linux-kernel - Re: [PATCH 07/11] x86/fault: Split the OOPS code out from no

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Message-ID: <CALCETrXUOJ1RNHCGZjp_Xk0DTvXaGXKy6t1b5vFHa3CqDenoRw@mail.gmail.com>
Date:   Tue, 9 Feb 2021 12:09:48 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 07/11] x86/fault: Split the OOPS code out from no_context()

On Wed, Feb 3, 2021 at 10:56 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Sun, Jan 31, 2021 at 09:24:38AM -0800, Andy Lutomirski wrote:
> > Not all callers of no_context() want to run exception fixups.
> > Separate the OOPS code out from the fixup code in no_context().
> >
> > Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Signed-off-by: Andy Lutomirski <luto@...nel.org>
> > ---
> >  arch/x86/mm/fault.c | 116 +++++++++++++++++++++++---------------------
> >  1 file changed, 62 insertions(+), 54 deletions(-)
> >
> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 1939e546beae..6f43d080e1e8 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -618,53 +618,20 @@ static void set_signal_archinfo(unsigned long address,
> >  }
> >
> >  static noinline void
> > -no_context(struct pt_regs *regs, unsigned long error_code,
> > -        unsigned long address, int signal, int si_code)
> > +page_fault_oops(struct pt_regs *regs, unsigned long error_code,
>
> Not sure about this name - it still tries to recover:
> efi_recover_from_page_fault().
>
> Judging by where it is called, maybe no_context_tail() or
> no_context_oops() or no_context_finish_me_already()...
>
> Yah, I haz no better idea. :-\
>
> ...
>
> > @@ -739,6 +692,61 @@ no_context(struct pt_regs *regs, unsigned long error_code,
> >       oops_end(flags, regs, sig);
> >  }
> >
> > +static noinline void
> > +no_context(struct pt_regs *regs, unsigned long error_code,
> > +        unsigned long address, int signal, int si_code)
> > +{
> > +     if (user_mode(regs)) {
> > +             /*
> > +              * This is an implicit supervisor-mode access from user
> > +              * mode.  Bypass all the kernel-mode recovery code and just
> > +              * OOPS.
> > +              */
> > +             goto oops;
>
> Just do
>
>                 return page_fault_oops(...);
>
> here and get rid of the label.

I'm going to skip this one, because that code is deleted later in the
series, and fixing it here just adds more churn.