Re: Q: user_enable_single_step() && update_debugctlmsr()

[Sebastian Andrzej Siewior]

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.

> Oleg.
Sebastian
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