Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr

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From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr
Date	Sat, 27 Jun 2015 10:40:01 +0200
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* Prarit Bhargava <prarit@redhat.com> wrote:

> Customers write system monitoring software for single systems as well as
> clusters.  In load-balancing software it is useful to know how "busy" a
> core is.  Unfortunately the only way to get this data is to run as root,
> or use setcap to allow userspace access for particular programs.  Both of
> these options are clunky at best.
> 
> This patch allows read access to the msr dev files which should be okay.
> No damage can be done by reading the MSR values and it allows non-root
> users to run system monitoring software.
> 
> The turbostat code specifically checks for CAP_SYS_RAWIO, which it
> shouldn't have to and I've removed that code.  Additionally I've modified
> the turbostat man page to remove documentation about configuring
> CAP_SYS_RAW_IO.
> 
> Note: Write access to msr is still restricted with this patch.
> 
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: x86@kernel.org
> Cc: Len Brown <len.brown@intel.com>
> Cc: Prarit Bhargava <prarit@redhat.com>
> Cc: Dasaratharaman Chandramouli <dasaratharaman.chandramouli@intel.com>
> Signed-off-by: Prarit Bhargava <prarit@redhat.com>
> ---
>  arch/x86/kernel/msr.c                 |   11 ++++++++---
>  tools/power/x86/turbostat/turbostat.8 |    8 --------
>  tools/power/x86/turbostat/turbostat.c |   17 -----------------
>  3 files changed, 8 insertions(+), 28 deletions(-)

So what's wrong with exposing them as a simplified PMU driver?

That way we only expose the ones we want to - plus tooling can use all the rich 
perf features that can be used around this. (sampling, counting, call chains, 
etc.)

Thanks,

	Ingo
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Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr Ingo Molnar <mingo@kernel.org> - 2015-06-27 10:40 +0200

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