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Re: Dealing with the NMI mess

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On Thu, Jul 23, 2015 at 2:35 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Jul 23, 2015 at 2:20 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> So the NMI could trigger userspace debug register faults, and simply
>> disabling them would make the whole debug register thing entirely
>> unreliable.
>
> We could easily set something to re-enable them for when we actually
> return to user space. I'd be ok with just setting the
> _TIF_USER_WORK_MASK.
>
> But even that should not be a requirement for the basic stability and
> core integrity of the kernel. Not like the current horrid mess with
> NMI nesting and ESP fixing etc.
>
> And realistically, nobody will ever even notice. So the whole "ok, we
> can use _TIF_USER_WORK_MASK to re-enable dr7" is a tiny tiny detail
> that is more like cleaning up things, not a core issue.
>

Or we just re-enable them on the way out of NMI (i.e. the very last
thing we do in the NMI handler).  I don't want to break regular
userspace gdb when perf is running.

--Andy
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Thread

Re: Dealing with the NMI mess Peter Zijlstra <peterz@infradead.org> - 2015-07-23 23:30 +0200
  Re: Dealing with the NMI mess Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-23 23:40 +0200
    Re: Dealing with the NMI mess Andy Lutomirski <luto@amacapital.net> - 2015-07-23 23:50 +0200
      Re: Dealing with the NMI mess Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-24 00:00 +0200
        Re: Dealing with the NMI mess Andy Lutomirski <luto@amacapital.net> - 2015-07-24 00:10 +0200
          Re: Dealing with the NMI mess Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-24 00:10 +0200
          Re: Dealing with the NMI mess Peter Zijlstra <peterz@infradead.org> - 2015-07-24 12:30 +0200
        Re: Dealing with the NMI mess Peter Zijlstra <peterz@infradead.org> - 2015-07-24 13:10 +0200

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