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Date: Wed, 12 Dec 2012 21:31:29 -0700
From: David Ahern <dsahern@gmail.com>
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Subject: Re: [GIT PULL] perf changes for v3.8
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On 12/12/12 8:51 PM, Linus Torvalds wrote:
> SO WHY DON'T YOU JUST DO THAT THEN?
>
> Disable PEBS on Vt-x enter and re-enable it on exit. End of story.
> Exactly like you say.

See commit 26a4f3c0. But that was not enough. Requiring exclude_guest 
was another required piece. If you want to see the discussion: 
https://lkml.org/lkml/2012/7/9/264

>
> But doing it this way was wrong. Switch that "exclude_guest" attribute
> around, and admit that "H" was bogus, and that the right thing to do
> was to add a "V" flag that sets the "force_guest" flag instead.

I understand this is annoying. Older binaries on newer kernels was the 
only case I could not fix. (I guess a message could be added kernel side 
to at least give a hint.) But the alternative -- based on code that has 
existed for some time -- is for older binaries to crash VMs.

David