Re: [patch 2/2] x86 NMI-safe INT3 and Page Fault

Avi Kivity
2010-07-16T19:32:55Z

On 07/16/2010 10:28 PM, Andi Kleen wrote:
>
>> I really hope noone ever gets the idea of touching user space from an
>> NMI handler, though, and expecting it to work...
>>
> It can make sense for a backtrace in a profiler.
>
> In fact perf is nearly doing it I believe, but moves
> it to the self IPI handler in most cases.
>

Interesting, is the self IPI guaranteed to execute synchronously after
the NMI's IRET? Or can the core IRET faster than the APIC and so we get
the backtrace at the wrong place?

(and does it matter? the NMI itself is not always accurate)

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.