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SubjectRe: [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determine nested NMI

* Steven Rostedt <rostedt@goodmis.org> wrote:

> On Sun, 2012-02-19 at 13:56 +0100, Ingo Molnar wrote:
> > * Steven Rostedt <rostedt@goodmis.org> wrote:
> >
> > > Ingo,
> > >
> > > I found that it is possible for userspace to prevent an NMI
> > > from triggering while it is running by setting its stack
> > > pointer to that of the NMI stack. This tricks the NMI nested
> > > algorithm in thinking that the NMI is nested. The easy
> > > solution to this is to test the %rip to make sure that the NMI
> > > happened in kernel mode before testing for nesting.
> >
> > Ouch...
>
> Note, it does not seem to cause any destruction, but screw up
> profiling.

Except if the source of the NMI was not profiling, right?

Thanks,

Ingo


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