Hi. Today I noticed by accident that starting from Aug 4 (at least) all my emails went to nowhere. I am resending some of them...
On 08/06, Sebastian Andrzej Siewior wrote: > > On 08/03/2012 06:29 PM, Oleg Nesterov wrote: > >> Assuming this series passes the review of course. And it would >> be really nice if someone reviews 2/2, I am not confident that >> I fully understand this DEBUGCTLMSR_BTF magic. > > Here is how the processor disables the BTF: > > | The processor clears the BTF flag when it generates a debug > | exception. The debugger must set the BTF flag before resuming program > | execution to continue single-stepping on branches. > > This was a quote from "253668-039US, May 2011" page 16-17. OK, thanks, > So I think __switch_to_extra() should set the bit before putting the > task on the CPU. Why? > If this bit is enabled on the wrong CPU then in will > remain set forever if single steeping has not been / will not be > enabled. I don't follow, could you explain in details? Just in case, X86_EFLAGS_TF sits in task_pt_regs(next), it has no effect until the task returns to usermode. We only need to ensure DEBUGCTLMSR_BTF was set/cleared correctly when it actually returns. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
