linux-kernel - Re: [PATCH 6/5] x86/fault: Clean up the page fault oops decoder a bit

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Date:   Tue, 4 Dec 2018 12:11:05 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 6/5] x86/fault: Clean up the page fault oops decoder a bit

On Tue, Dec 4, 2018 at 11:52 AM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Tue, Dec 04, 2018 at 11:47:10AM -0800, Andy Lutomirski wrote:
> > On Tue, Dec 4, 2018 at 11:34 AM Sean Christopherson
> > <sean.j.christopherson@...el.com> wrote:
> > >
> > > On Tue, Dec 04, 2018 at 11:22:25AM -0800, Andy Lutomirski wrote:
> > > > On Tue, Nov 27, 2018 at 7:32 AM Sean Christopherson
> > > > <sean.j.christopherson@...el.com> wrote:
> > > > > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > > > > index 2ff25ad33233..510e263c256b 100644
> > > > > --- a/arch/x86/mm/fault.c
> > > > > +++ b/arch/x86/mm/fault.c
> > > > > @@ -660,8 +660,10 @@ show_fault_oops(struct pt_regs *regs, unsigned long error_code, unsigned long ad
> > > > >         err_str_append(error_code, err_txt, X86_PF_RSVD,  "[RSVD]" );
> > > > >         err_str_append(error_code, err_txt, X86_PF_INSTR, "[INSTR]");
> > > > >         err_str_append(error_code, err_txt, X86_PF_PK,    "[PK]"   );
> > > > > -
> > > > > -       pr_alert("#PF error: %s\n", error_code ? err_txt : "[normal kernel read fault]");
> > > > > +       err_str_append(~error_code, err_txt, X86_PF_USER, "[KERNEL]");
> > > > > +       err_str_append(~error_code, err_txt, X86_PF_WRITE | X86_PF_INSTR,
> > > > > +                                                         "[READ]");
> > > > > +       pr_alert("#PF error code: %s\n", err_txt);
> > > > >
> > > >
> > > > Seems generally nice, but I would suggest making the bit-not-set name
> > > > be another parameter to err_str_append().  I'm also slightly uneasy
> > > > about making "KERNEL" look like a bit, but I guess it doesn't bother
> > > > me too much.
> > >
> > > What about "SUPERVISOR" instead of "KERNEL"?  It'd be consistent with
> > > the SDM and hopefully less likely to be misconstrued as something else.
> >
> > Or even just [!USER], perhaps.
>
> I thought about that too, but the pedant in me didn't like the inconsistency
> of doing "READ" instead of "[!WRITE] [!INSTR]", and IMO "READ" is a lot more
> readable (no pun intended).  I also like having completely different text,
> makes it harder to miss a single "!" and go down the wrong path.

Fair enough.  I'm sold.