linux-kernel - Re: [PATCH 0/6] x86/entry: disallow #DB more

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Date:   Fri, 29 May 2020 10:00:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lai Jiangshan <jiangshanlai+lkml@...il.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        andrew.cooper3@...rix.com, daniel.thompson@...aro.org
Subject: Re: [PATCH 0/6] x86/entry: disallow #DB more

On Fri, May 29, 2020 at 07:05:54AM +0800, Lai Jiangshan wrote:
> On Fri, May 29, 2020 at 6:48 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Fri, May 29, 2020 at 06:42:46AM +0800, Lai Jiangshan wrote:
> > > On Fri, May 29, 2020 at 4:25 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > > >
> > > > These patches disallow #DB during NMI/#MC and allow removing a lot of fugly code.
> > > >
> > >
> > > Hello
> > >
> > > Will #DB be allowed in #DF?
> >
> > No, that whole thing is noinstr.
> 
> But it calls many functions, including die(), panic().
> We don't want #DB to interfere how it die() and panic().
> Since it is in fragile #DF, the #DB may mess it up and
> make #DF fails to report and die.

The only recoverable #DF is the ESPFIX shit. If we do not take that,
we're on the way to panic(), I really can't be arsed if you crash the
box before that, we're going to die anyway.