Re: [PATCH] perf, x86: Fall back to vmalloc for BTS buffer allocation

[Peter Zijlstra]

On Wed, Sep 10, 2014 at 11:27:44AM -0700, Andi Kleen wrote:
> > Note that since then we have actually fixed the 'cannot fault from NMI
> > context' thing, so we should be able to actually take those faults. I
> > suspect we can simply remove those WARNs from the vmalloc fault path,
> > but it would need double checking to see if there's no other reasons.
> 
> I think we actually need to use vmalloc_sync_all, because the PEBS/DS
> microcode may do the first access, and those lose events when
> the page is not present.

You'll need to convince Linus: https://lkml.org/lkml/2010/7/14/478
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