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

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Date:   Fri, 7 Dec 2018 11:18:48 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     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>, bp@...en8.de,
        the arch/x86 maintainers <x86@...nel.org>,
        Peter Anvin <hpa@...or.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Rik van Riel <riel@...riel.com>, yu-cheng.yu@...el.com,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] x86/fault: Decode and print #PF oops in human readable
 form

On Fri, Dec 07, 2018 at 10:52:49AM -0800, Linus Torvalds wrote:
> On Fri, Dec 7, 2018 at 10:44 AM Sean Christopherson
> <sean.j.christopherson@...el.com> wrote:
> >
> > Remove the per-bit decoding of the error code and instead print the raw
> > error code followed by a brief description of what caused the fault, the
> > effective privilege level of the faulting access, and whether the fault
> > originated in user code or kernel code.
> 
> This doesn't quite work as-is, though.
> 
> For example, at least the PK bit is independent of the other bits and
> would be interesting in the human-legible version, but doesn't show up
> there at all.

Heh, I actually intentionally omitted protection keys thinking it'd be
superfluous, i.e. "go look at the error code bits if you care that much".

> That said, I think the end result might be more legible than the
> previous version, so this approach may well be good, it just needs at
> least that "permissions violation"  part to be extended with whether
> it was PK or not.
> 
> Also, shouldn't we show the SGX bit too as some kind of "during SGX"
> extension on the "in user/kernel space" part?

The SGX bit isn't defined in mainline yet.  But yeah, I can see how
printing e.g. "SGX EPCM violation" would be a lot more helpful than
a vanilla "permissions violation".  I'll send a v2 with the PK bit
added and a slightly reworded changelog.