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<H1>MSR</H1>
Section: Linux Programmer's Manual (4)<BR>Updated: 2009-03-31<BR><A HREF="#index">Index</A>
<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
<A NAME="lbAB">&nbsp;</A>
<H2>NAME</H2>
msr - x86 CPU MSR access device
<A NAME="lbAC">&nbsp;</A>
<H2>DESCRIPTION</H2>
<I>/dev/cpu/CPUNUM/msr</I>
provides an interface to read and write the model-specific
registers (MSRs) of an x86 CPU.
<I>CPUNUM</I>
is the number of the CPU to access as listed in
<I>/proc/cpuinfo</I>.
<P>
The register access is done by opening the file and seeking
to the MSR number as offset in the file, and then
reading or writing in chunks of 8 bytes.
An I/O transfer of more than 8 bytes means multiple reads or writes
of the same register.
<P>
This file is protected so that it can be read and written only by the user
<I>root</I>,
or members of the group
<I>root</I>.
<A NAME="lbAD">&nbsp;</A>
<H2>NOTES</H2>
The
<I>msr</I>
driver is not auto-loaded.
On modular kernels you might need to use the following command
to load it explicitly before use:
<P>
$ modprobe msr
<P>
<A NAME="lbAE">&nbsp;</A>
<H2>SEE ALSO</H2>
Intel Corporation Intel 64 and IA-32 Architectures
Software Developer's Manual Volume 3B Appendix B,
for an overview of the Intel CPU MSRs.
<A NAME="lbAF">&nbsp;</A>
<H2>COLOPHON</H2>
This page is part of release 5.05 of the Linux
<I>man-pages</I>
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
<P>
<HR>
<A NAME="index">&nbsp;</A><H2>Index</H2>
<DL>
<DT id="1"><A HREF="#lbAB">NAME</A><DD>
<DT id="2"><A HREF="#lbAC">DESCRIPTION</A><DD>
<DT id="3"><A HREF="#lbAD">NOTES</A><DD>
<DT id="4"><A HREF="#lbAE">SEE ALSO</A><DD>
<DT id="5"><A HREF="#lbAF">COLOPHON</A><DD>
</DL>
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