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From: Ingo Molnar <mingo@elte.hu>
To: Roland McGrath <roland@redhat.com>
Cc: Jan Beulich <jbeulich@novell.com>,
	tglx@linutronix.de, hpa@zytor.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: fix typo(?) in step.c
Date: Thu, 6 Mar 2008 12:34:13 +0100	[thread overview]
Message-ID: <20080306113413.GD17906@elte.hu> (raw)
In-Reply-To: <20080306075223.BA28B2700FD@magilla.localdomain>


* Roland McGrath <roland@redhat.com> wrote:

> The block-step test only tested that PTRACE_SINGLEBLOCK worked right. 
> I just souped it up to also test that PTRACE_SINGLESTEP still works 
> immediately afterwards.  This still does not show any problem from 
> this bug.  The case that would be broken by it is rather more arcane.  
> I haven't worked out the test case that fails with the bogon.

my interpretation of the bug would be that we fail to mask out the 
block-step MSR bit [because we mask out bit 25 instead of bit 1], and 
hence the bug would cause that MSR bit to stay enabled in other tasks 
too.

So in theory the bug should manifest itself as block-step mode never 
clearing itself, once activated. (but this would never leak into other 
tasks because we've got the thread.debugctlmsr abstraction that protects 
them)

	Ingo

  parent reply	other threads:[~2008-03-06 11:34 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-05  8:36 Jan Beulich
2008-03-05 13:41 ` Ingo Molnar
2008-03-06  7:52   ` Roland McGrath
2008-03-06 11:28     ` Ingo Molnar
2008-03-06 12:03       ` Roland McGrath
2008-03-06 13:11         ` Ingo Molnar
2008-03-10 11:53           ` Jan Beulich
2008-03-11  3:44             ` Roland McGrath
2008-03-06 11:34     ` Ingo Molnar [this message]
2008-03-06 12:16       ` Roland McGrath
2008-03-06 13:13         ` Ingo Molnar

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