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Subject: Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting
From: Steven Rostedt <rostedt@goodmis.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Dave Jones <davej@redhat.com>, Andi Kleen <ak@linux.intel.com>
Date: Thu, 31 May 2012 16:56:51 -0400
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On Thu, 2012-05-31 at 13:39 -0700, H. Peter Anvin wrote:
> On 05/31/2012 01:35 PM, Steven Rostedt wrote:
> > 
> > Thus only the debug stack does the stack TSS trick.
> > 
> > Is this what you were looking for? (God, it just shows how much time
> > I've been spending on this crap, as I was able to find all this by
> > memory and not grepping for it :-p )
> > 
> 
> That's why I asked instead of pulled it up myself.
> 
> However, what is missing is what the permitted transitions are.  This
> affects the options.

Only the debug stack changes. These happen in the two places I already
mentioned.

One, the switch of the IDT in NMI (to convert the IST from 4 to 0, and
just keep the same stack).

Two, is the trick in the paranoidzeroentry_ist code (adding the debug
stack). That changes the DEBUG stack pointer.

-- Steve