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

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Date:	Thu, 10 Dec 2015 15:26:43 -0700
From:	Jeff Merkey <linux.mdb@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Andy Lutomirski <luto@...capital.net>,
	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

I'll submit a second patch later this evening with a graceful message
when this happens.  I need to look over this code path -- its in a
very mature section of code and detecting this condition (bp not being
present) may break other code paths and subsystems ifs not done very
carefully.  The current dr7 check works and I have tested this code,
but does not print a message.



On 12/10/15, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Thu, 10 Dec 2015, Andy Lutomirski wrote:
>> On brief inspection, this smells like a microcode bug.  Can you send
>> /proc/cpuinfo output?
>>
>> If this is the issue, I'm not sure we want to be in the business of
>> working around localized microcode bugs and, if we do, then I think we
>> should explicitly detect the bug and log about it.
>
> I think we should handle such stuff gracefully. Yes, we should log it
> and we also should check what the contents of the debug registers are.
>
> If dr7 has a break point enabled w/o perf having one installed then we
> know that someone did a horrible hackery ....
>
> Thanks,
>
> 	tglx
>
>
>
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