Xen devel - Jan 2009 - [PATCH]: Let dom0 write to the APERF and MPERF MSR''s

All,
     If dom0 is controlling the frequency scaling (which it still is in RHEL-5),
and it''s using the new acpi-cpufreq code from upstream (which it is in
5.3),
then it will attempt to wrmsr() to the MSR_IA32_APERF and MSR_IA32_MPERF
MSR''s
(to do performance measuring, I believe).  With the current hypervisor, this
results in a lot of:

(XEN) traps.c:1761:d0 Domain attempted WRMSR 00000000000000e8 from
00000029:d7ca940f to 00000000:00000000.

messages.  I believe it is safe to let the dom0 do this MSR write, so the
attached patch just allows the write to go through.  This eliminates the message
spam, and probably allows acpi-cpufreq work to a certain extent (although I have
not verified the latter).

The patch was generated and tested on a RHEL-5 (3.1-based) hypervisor, but
should apply with a little massaging to xen-unstable.

Signed-off-by: Chris Lalancette <clalance@redhat.com>


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