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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: mingo@kernel.org, hpa@zytor.com, eranian@google.com,
	linux-kernel@vger.kernel.org, fweisbec@gmail.com,
	akpm@linux-foundation.org, tglx@linutronix.de,
	linux-tip-commits@vger.kernel.org
Subject: Re: [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples
Date: Fri, 06 Jul 2012 20:12:09 +0200
Message-ID: <1341598329.7709.57.camel@twins> (raw)
In-Reply-To: <CA+55aFxY7SqwSQWuRXSg+W=ftp9FtCT1MMEqMiCi1H279Fis-A@mail.gmail.com>

On Fri, 2012-07-06 at 09:29 -0700, Linus Torvalds wrote:
> On Thu, Jul 5, 2012 at 11:20 PM, tip-bot for Peter Zijlstra
> <a.p.zijlstra@chello.nl> wrote:
> >
> > Several perf interrupt handlers (PEBS,IBS,BTS) re-write regs->ip but
> > do not update the segment registers. So use an regs->ip based test
> > instead of an regs->cs/regs->flags based test.
> 
> Christ, people, YOU CANNOT DO THIS!
> 
> It is never *ever* valid to test the IP to see if you're in kernel
> space or user space. People can do various odd segments etc, the IP is
> totally meaningless.
> 
> If the perf handlers fake the IP information, they had better fake the
> CS/eflags information too. Because it is *wrong* to look at IP. Don't
> do it.

PEBS, BTS, LBR don't have CS. PEBS does have eflags.

If we cannot do this I'm not sure what we can do :/

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-06  6:20 tip-bot for Peter Zijlstra
2012-07-06 16:29 ` Linus Torvalds
2012-07-06 18:12   ` Peter Zijlstra [this message]
2012-07-06 18:16     ` Linus Torvalds
2012-07-06 18:34       ` Linus Torvalds
2012-07-06 20:48         ` Peter Zijlstra
2012-07-06 20:59           ` Linus Torvalds
2012-07-09 11:23         ` Peter Zijlstra
2012-07-09 17:55           ` Linus Torvalds
2012-07-10  9:02             ` Peter Zijlstra
2012-07-10  9:48               ` Ingo Molnar
2012-07-10  9:50               ` Peter Zijlstra
2012-07-10  9:52                 ` Peter Zijlstra
2012-07-10  9:55                 ` Ingo Molnar
2012-07-31 17:57               ` [tip:perf/urgent] perf/x86: Fix USER/ KERNEL tagging of samples properly tip-bot for Peter Zijlstra
2012-07-09 18:41           ` [tip:perf/core] perf/x86: Fix USER/KERNEL tagging of samples Ingo Molnar
2012-07-10  7:54             ` Peter Zijlstra
2012-07-10  8:02               ` Ingo Molnar
2012-07-10  8:21               ` Ingo Molnar
2012-07-10  8:52                 ` Peter Zijlstra
2012-07-10  9:48                   ` Ingo Molnar
2012-07-31 18:11                     ` H. Peter Anvin

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