linux-kernel - Re: privilege levels and kernel mode

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Date:	Sun, 15 Oct 2006 22:02:19 +0200 (MEST)
From:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
To:	ranjith kumar <ranjit_kumar_b4u@...oo.co.uk>
cc:	linux-kernel@...r.kernel.org
Subject: Re: privilege levels and kernel mode

>Hi,
>    I am using pentium-4 processor. My operating
>system  is Linux version 2.4.22-1.2199.nptl
>
>  I want to measure performance events like number of
>memory reads, number of cache misses occured while
>running  a "C" program. For that I have to wright some
>values into "Model specific registers of pentium-4
>processor". But those registers can be written ONLY at
>privilege level of zero of pentium4 processor.
>
> We know that application programs we write (for
>example any C program)are run at privilege
>level-3(user mode).
>
>I know how to include assembly instructions in a C
>program to wtrite into "Model specific registers". But
>that program has to be run at privilege level zero.
>
>How to run a C program at privilege level zero??

The short answer: You can't.

The long answer: You have to write a kernel module to do what you need.

The best answer: Use /dev/cpu/0/msr.

>Can any one help me?
>
>Thanks in advance.
>
> 
>
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	-`J'
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