linux-kernel - Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)

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Date:	Fri, 23 Dec 2011 11:56:08 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>, Avi Kivity <avi@...hat.com>,
	Robert Richter <robert.richter@....com>,
	Benjamin Block <bebl@...eta.org>,
	Hans Rosenfeld <hans.rosenfeld@....com>, hpa@...or.com,
	tglx@...utronix.de, suresh.b.siddha@...el.com, eranian@...gle.com,
	brgerst@...il.com, Andreas.Herrmann3@....com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Benjamin Block <benjamin.block@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)


* Gleb Natapov <gleb@...hat.com> wrote:

> On Tue, Dec 20, 2011 at 07:40:04PM +0100, Ingo Molnar wrote:
> > > The point is, if user-space re-programs LWP it will continue 
> > > to write its samples to the new ring-buffer virtual-address 
> > > set up by user-space. It will still use that virtual address 
> > > in another address-space after a task-switch. This allows 
> > > processes to corrupt memory of other processes. [...]
> > 
> > That's nonsense. As i said it my previous mail the LWPC 
> > should be per task and switched on task switch - just like 
> > the DS/PEBS context is.
> 
> Is it? Looking at arch/x86/kernel/cpu/perf_event_intel_ds.c it 
> seems like DS is per cpu, not per task.

We flush it on context switch and reuse it for the next task via 
the x86_pmu.drain_pebs() callback - so the buffering of PEBS 
events is per task.

Thanks,

	Ingo
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