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Date: Fri, 24 Nov 2017 22:49:09 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [crash] PANIC: double fault, error_code: 0x0
Message-ID: <20171124214909.qi5v3rgka6ibtbpj@gmail.com>
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* Andy Lutomirski <luto@kernel.org> wrote:

> On Fri, Nov 24, 2017 at 12:22 PM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > * Ingo Molnar <mingo@kernel.org> wrote:
> >
> >> This is a repost of the latest entry-stack plus Kaiser bits from Andy Lutomirski
> >> (v3 series from today) and Dave Hansen (kaiser-414-tipwip-20171123 version),
> >> on top of latest tip:x86/urgent (12a78d43de76).
> >>
> >> This version is pretty well tested, at least on the usual x86 tree test systems.
> >> It has a couple of merge mistakes fixed, the biggest difference is in patch #22:
> >>
> >>   x86/mm/kaiser: Prepare assembly for entry/exit CR3 switching
> >>
> >> The other patches are identical or very close to what I posted earlier today.
> >
> > Here's a new bug, on a testsystem I get the double fault boot crash attached
> > below. The same bzImage crashes on other systems as well, so it's not CPU
> > dependent.
> >
> > Via Kconfig-bisection I have narrowed it down to the following .config detail:
> > it's triggered by _disabling_ CONFIG_DEBUG_ENTRY and enabling CONFIG_KAISER=y.
> >
> > I.e. one of the sanity checks of CONFIG_DEBUG_ENTRY has some positive side effect.
> 
> That's weird and definitely not intentional.

Btw., can you reproduce the crash by disabling CONFIG_DEBUG_ENTRY with 
CONFIG_KAISER=y?

Thanks,

	Ingo