linux-kernel - Re: [PATCH 2/2] x86/uprobes: implement x86 specific arch_uprobe_*

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Message-ID: <20120802045831.GA8538@in.ibm.com>
Date:	Thu, 2 Aug 2012 10:28:31 +0530
From:	Ananth N Mavinakayanahalli <ananth@...ibm.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, srikar@...ux.vnet.ibm.com, roland@...k.frob.com
Subject: Re: [PATCH 2/2] x86/uprobes: implement x86 specific
	arch_uprobe_*_step

On Wed, Aug 01, 2012 at 03:43:37PM +0200, Oleg Nesterov wrote:

...

> However, I am not sure we can trust it. We are in kernel mode,
> DEBUGCTLMSR_BTF can be cleared by kprobes (Ananth, please correct me).
> I think we need to check TIF_BLOCKSTEP.

Kprobes resets DEBUGCTLMSR_BTF only if we have to single-step in
hardware. It puts the flag back if TIF_BLOCKSTEP is set, after the
single-step is complete; so yes, a better check is TIF_BLOCKSTEP.

Ananth

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