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Date: Mon, 7 Sep 2015 09:42:18 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "Maciej W. Rozycki" <macro@linux-mips.org>
Cc: Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@amacapital.net>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Brian Gerst <brgerst@gmail.com>
Subject: Re: Dealing with the NMI mess
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* Maciej W. Rozycki <macro@linux-mips.org> wrote:

>  I did some work on this a few years ago, including emulating DR0-7 accesses in 
> software down the JTAG handler upon a General Detect fault to keep the kernel 
> both happy and away from real debug registers. ;) Yes, you can debug any 
> software with this stuff, including the Linux kernel: set instruction and data 
> breakpoints, single-step it, poke at all hardware registers, including 
> descriptor registers not otherwise accessible (you can set funny modes for 
> segments, also in the 64-bit mode), etc.  One complication though is you operate 
> on physical addresses when poking at memory, you can't ask the CPU's MMU to 
> remap them for you (you can walk page tables manually of course, just as the MMU 
> would).

Essentially the ICE breakpoint instruction enters SMM mode?

Thanks,

	Ingo