linux-kernel - Re: [PATCH v2] x86/fault: Decode and print #PF oops in human readable form

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Message-ID: <CALCETrUu=qO4tHkk-QxKD_j687hKV56X9JvYv1YsdgtOy0urmQ@mail.gmail.com>
Date:   Fri, 7 Dec 2018 15:57:10 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v2] x86/fault: Decode and print #PF oops in human readable form

On Fri, Dec 7, 2018 at 2:14 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Fri, Dec 7, 2018 at 2:06 PM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > Looking at it again, my own personal preference would be to swap the order
> > of the #PF lines.
>
> Yeah, probably.
>
> Also:
>
> > [  160.246820] BUG: unable to handle kernel paging request at ffffbeef00000000
> > [  160.247517] #PF: supervisor-privileged instruction fetch from kernel code
> > [  160.248085] #PF: error_code(0x0010) - not-present page
>
> With this form, I think the "kernel" in the first line is actually
> misleading. Yes, it's a #PF for the kernel, but then the "kernel" on
> the second line talks about what mode we were in when it happened, so
> we have two different meanings of "kernel" on two adjacent lines.

I'm okay with this variant.  I have a slight preference for:

#PF: supervisor-privileged instruction fetch from kernel code
#PF error_code: 0x0010 [READ]

Which is what we'd get from Sean's patch plus my patch here:

https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/mm&id=ccfb1941f90153818c07fb1a7dc22121a970d252

Sean, what do you think?

> So maybe  that "BUG: unable to handle kernel paging request" message
> should be something like
>
>   "BUG: unable to handle page fault for address ffffbeef00000000"
>
> instead? Does that make sense to people?

Yes please.