linux-kernel - Re: [RFC 5/5] x86,perf: Only allow rdpmc if a perf

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Message-ID: <20141020112413.56450095@mschwide>
Date:	Mon, 20 Oct 2014 11:24:13 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Erik Bosman <ebn310@....vu.nl>, mpe@...erman.id.au,
	anton@...ba.org, brueckner@...ux.vnet.ibm.com
Subject: Re: [RFC 5/5] x86,perf: Only allow rdpmc if a perf_event is mapped

On Mon, 20 Oct 2014 10:48:13 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> >  - cpumsf_pmu_event_idx is the same as power_pmu_event_idx.
> 
> Oh cute, lets ask the s390 people, do you guys have a userspace
> instruction to read the actual counter value?

The "extract cpu counter" ECCTR instruction can be authorized to
be used in user-space with a bit in CR0. With the current code
this bit is not set, the cpu measurement facility is not usable
in user space without a patch to the kernel.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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