[PATCH] cpufreq bug fixes (stable/cpufreq.bugfixes) for 3.0 (or 3.1).

[Konrad Rzeszutek Wilk]

The two patches attached make the cpufreq and powernowk8 driver more robust on
badly behaving machines (or hypervisors not passing through proper rmsdr calls).

Specifically during the testing of v3.0-rc2, Tobias found a peculiar issue with
his AMD machine: http://mid.gmane.org/20110613202622.GC20616@xxxxxxxxxxxxxxxxx

It looks as the Xen hypervisor lacks passthrough RDMSR entries for the PowerNow K8
voltage settings (MSR_FIDVID_STATUS and MSR_FIDVID_CTL) resulting in the writes/reads
giving the value zero. The end result being that the cpufreq stats code BUG()s on
incorrect index of the freq table.

The patches are also located at:

git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/cpufreq.bugfixes

The crash looks as follow:

powernow-k8: Found 1 AMD Athlon(tm) 64 Processor 3700+ (1 cpu cores) (version 2.20.00)
powernow-k8: fid 0x2 (1000 MHz), vid 0x12
powernow-k8: fid 0xa (1800 MHz), vid 0xa
powernow-k8: fid 0xc (2000 MHz), vid 0x8
powernow-k8: fid 0xe (2200 MHz), vid 0x8
Marking TSC unstable due to cpufreq changes
powernow-k8: fid trans failed, fid 0x2, curr 0x0
BUG: unable to handle kernel paging request at ffff880807e07b78
IP: [<ffffffff81479163>] cpufreq_stats_update+0x46/0x5b
.. snip..
Pid: 1, comm: swapper Not tainted 3.0.0-rc2 #45 MICRO-STAR INTERNATIONAL CO., LTD MS-7094/MS-7094
..snip..
Call Trace:
 [<ffffffff81479248>] cpufreq_stat_notifier_trans+0x48/0x7c
 [<ffffffff81095d68>] notifier_call_chain+0x32/0x5e
 [<ffffffff81095e6b>] __srcu_notifier_call_chain+0x47/0x63
 [<ffffffff81095e96>] srcu_notifier_call_chain+0xf/0x11
 [<ffffffff81477e7a>] cpufreq_notify_transition+0x111/0x134
 [<ffffffff8147b0d4>] powernowk8_target+0x53b/0x617
 [<ffffffff8147723a>] __cpufreq_driver_target+0x2e/0x30
 [<ffffffff8147a127>] cpufreq_governor_dbs+0x339/0x356
 [<ffffffff81477394>] __cpufreq_governor+0xa8/0xe9
 [<ffffffff81477525>] __cpufreq_set_policy+0x132/0x13e
 [<ffffffff8147848d>] cpufreq_add_dev_interface+0x272/0x28c


Konrad Rzeszutek Wilk (2):
      [CPUFREQ] powernow-k8: Don't notify of successful transition if we failed.
      [CPUFREQ]: Don't set stat->last_index to -1 if the pol->cur has incorrect value.

 arch/x86/kernel/cpu/cpufreq/powernow-k8.c |    7 ++++++-
 drivers/cpufreq/cpufreq_stats.c           |    8 +++++---
 2 files changed, 11 insertions(+), 4 deletions(-)
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