linux-kernel - Re: perf: fuzzer crashes immediately on AMD system

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Date:   Mon, 22 Aug 2016 19:16:32 +0800
From:   Huang Rui <ray.huang@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Vince Weaver <vincent.weaver@...ne.edu>
CC:     <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: perf: fuzzer crashes immediately on AMD system

Hi Peter, Vince

On Fri, Aug 19, 2016 at 12:01:30PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 18, 2016 at 10:46:31AM -0400, Vince Weaver wrote:
> > On Thu, 18 Aug 2016, Vince Weaver wrote:
> > 
> > > Tried the perf_fuzzer on my A10 fam15h/model13h system with 4.8-rc2 and it
> > > falls over more or less immediately.
> > > 
> > > This maps to variable_test_bit()
> > > 	called by ctx = find_get_context(pmu, task, event);
> > > 		in kernel/events/core.c:9467
> > > 
> > > It happens quickly enough I can probably track down the exact event that 
> > > causes this, if needed.
> > 
> > I have a one line reproducer:
> > 
> > 	perf stat -a -e amd_nb/config=0x37,config1=0x20/ /bin/ls
> 
> OK, cannot reproduce on my fam15h/model1h. I'll go dig through the
> various manuals to see if I can spot the fail.
> 
> Huang could you either prod someone at AMD or do yourself, audit the AMD
> perf code for all the various new models?

Actually, there might be some NBPMC event changes between model 0h-fh and
model 10h-1fh. Below are the documents of these two processors:

http://support.amd.com/TechDocs/42301_15h_Mod_00h-0Fh_BKDG.pdf
http://support.amd.com/TechDocs/42300_15h_Mod_10h-1Fh_BKDG.pdf

In section 3.16, it describes usage of NB Performance Counter Events.

Hope it helps. :-)

Thanks,
Rui