linux-kernel - Re: Q: user_enable_single_step() && update

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Message-ID: <20120801140121.GA5333@redhat.com>
Date:	Wed, 1 Aug 2012 16:01:21 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Roland McGrath <roland@...k.frob.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	ananth@...ibm.com, a.p.zijlstra@...llo.nl, mingo@...hat.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: Q: user_enable_single_step() && update_debugctlmsr()

On 08/01, Sebastian Andrzej Siewior wrote:
>
> On 08/01/2012 03:46 PM, Oleg Nesterov wrote:
>
>>>> But, worse, isn't it wrong? Suppose that debugger switches to
>>>> another TIF_SINGLESTEP&&   !TIF_BLOCKSTEP task, in this case
>>>> we "leak" DEBUGCTLMSR_BTF, no?
>>>
>>> __switch_to_xtra() should notice the difference in the TIF_BLOCKSTEP
>>> flag and disable it.
>>
>> And how it can notice the difference if there is no difference?
>>
>> (unless, of course debugger is TIF_BLOCKSTEP'ed).
>
> Yes. enable_step() sets DEBUGCTLMSR_BTF along with TIF_BLOCKSTEP.
> kprobes checks the same flag before touching DEBUGCTLMSR_BTF.

It seems that you replied to the wrong email or I am confused ;)

Let's ignore kprobes here.

Oleg.

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