linux-kernel - Re: [PATCH 1/1] Fix int1 recursion when no perf_bp

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Date:	Mon, 14 Dec 2015 09:09:14 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Jeff Merkey <linux.mdb@...il.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Borislav Petkov <bp@...en8.de>, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 1/1] Fix int1 recursion when no perf_bp_event is
 registeredy


A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing in e-mail?

* Jeff Merkey <linux.mdb@...il.com> wrote:

> I trigger it by writing to the dr7 and dr1, 2, 3 or four register and
> set an execute breakpoint without going through
> arch_install_hw_breakpoint.  When the breakpoint fires, the system
> crashes and hangs on the processor stuck in an endless loop inside the
> int1 handler in hw_breakpoint.c --

What is still not clear to me, can you trigger the hang not via some special 
kernel driver that goes outside regular APIs and messes with the state of the 
debug registers, but via the proper access methods, i.e. various user-space ABIs?

Thanks,

	Ingo
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