Subject: Re: [PATCH] powerpc: Partial revert of "Context switch more PMU related SPRs"

From: Anshuman Khandual <[email-masked]>
Date: Mon, 10 Jun 2013 09:48:17 +0530

On 06/06/2013 09:33 AM, Michael Ellerman wrote:
> In commit 59affcd I added context switching of more PMU SPRs, because
> they are potentially exposed to userspace on Power8. However despite me
> being a smart arse in the commit message it's actually not correct. In
> particular it interacts badly with a global perf record.

Could you please explain how it would interact badly with a global perf record.
If any user space try to mess around with the MMCR* registers itself, it would
definitely interfere with the kernel's own PMU config going on during perf record.
But thats how it works. So when we are actually dealing with MMCR* registers
directly, we should not invoke "perf record" session which can potential run on
the same PMU.

Regards
Anshuman