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Message-ID: <20080306113413.GD17906@elte.hu>
Date: Thu, 6 Mar 2008 12:34:13 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Roland McGrath <roland@...hat.com>
Cc: Jan Beulich <jbeulich@...ell.com>, tglx@...utronix.de,
hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: fix typo(?) in step.c
* Roland McGrath <roland@...hat.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
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