Re: [PATCH][GIT PULL][v3.3] x86: Test saved %rip in NMI to determinenested NMI

[Ingo Molnar]

* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> On Sun, 2012-02-19 at 13:56 +0100, Ingo Molnar wrote:
> > * Steven Rostedt <rostedt@xxxxxxxxxxx> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/