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

Andi Kleen
2010-07-16T19:34:11Z

On Fri, Jul 16, 2010 at 10:32:13PM +0300, Avi Kivity wrote:
> 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)

self ipi runs after the next STI (or POPF)

-Andi
--
ak@linux.intel.com -- Speaking for myself only.