linux-kernel - Re: perf_fuzzer compiled for x32 causes reboot

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Message-ID: <530FCE6C.4080808@zytor.com>
Date:	Thu, 27 Feb 2014 15:46:52 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Vince Weaver <vincent.weaver@...ne.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On 02/27/2014 03:30 PM, Steven Rostedt wrote:
> On Thu, 27 Feb 2014 14:52:54 -0800
> "H. Peter Anvin" <hpa@...or.com> wrote:
> 
>> On 02/27/2014 02:31 PM, Steven Rostedt wrote:
>>>
>>> Yeah, something is getting mesed up.
>>>
>>
>> What it *looks* like to me is that we try to nest the cr2 save/restore,
>> which doesn't nest because it is a percpu variable.
>>
>> ... except in the x86-64 case, we *ALSO* save/restore cr2 inside
>> entry_64.S, which makes the stuff in do_nmi completely redundant and
>> there for no good reason.
> 
> Peter, look at the code. That percpu cr2 is in a #ifdef CONFIG_X86_32
> section. That is, it isn't even executed. That's i386 code. The only
> place the cr2 is saved for x86_64 is in entry_64.S.
> 

Right, egg on my face.  However, I still think it would make more sense
for it to nest the way entry_64.S does if at all possible.

That makes this even more confusing, though.  I would still like to see
what happens with the patch I sent Vince.

	-hpa


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