linux-kernel - Re: [PATCH 1/3] perf, x86: Fix accidentally ack'ing a second event on intel perf counter

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100902203608.GA5914@lenovo>
Date:	Fri, 3 Sep 2010 00:36:08 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	mingo@...e.hu, peterz@...radead.org, robert.richter@....com,
	fweisbec@...il.com, linux-kernel@...r.kernel.org,
	ying.huang@...el.com, ming.m.lin@...el.com, yinghai@...nel.org,
	andi@...stfloor.org, eranian@...gle.com
Subject: Re: [PATCH 1/3] perf, x86: Fix accidentally ack'ing a second event
	on intel perf counter

On Thu, Sep 02, 2010 at 04:00:21PM -0400, Don Zickus wrote:
> On Thu, Sep 02, 2010 at 11:26:27PM +0400, Cyrill Gorcunov wrote:
> > Lets assume 1 counters is triggered and global bit is set as well
> > 
> > we have here
> > 
> > 	status = intel_pmu_get_status();
> > 
> > >  	perf_sample_data_init(&data, 0);
> > >  
> > > @@ -728,6 +728,7 @@ static int intel_pmu_handle_irq(struct pt_regs *regs)
> > >  
> > >  	loops = 0;
> > >  again:
> > > +	intel_pmu_ack_status(status);
> > 
> > So here we write just being read value back to CTRL register and _if_ new
> > overflow happened in this window we've cleared it without processing.
> 
> No, you have to write a '1' to clear.  If a new bit is set after we read
> it, then our 'status' var should have a '0' in that bit and thus will not
> get cleared when we ack it.
> 

Yeah, messed {0;1} values, thanks!

> Cheers,
> Don
> 
	-- Cyrill
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/