linux-kernel - Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

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Date:	Thu, 31 May 2012 16:56:51 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Dave Jones <davej@...hat.com>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 4/5] x86: Allow nesting of the debug stack IDT setting

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


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