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| author | Stefan Bader <stefan.bader@canonical.com> | 2013-01-22 13:37:21 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-01-27 20:49:02 -0800 |
| commit | 5f37ca96b441bcf255c4361a6b6e1873603a92f3 (patch) | |
| tree | e73b87273c3b7aa34ceebe7ea47d37045160b5a9 | |
| parent | 709084328e3a553ae6e27f5a8e826baecc3fd615 (diff) | |
| download | lwn-5f37ca96b441bcf255c4361a6b6e1873603a92f3.tar.gz lwn-5f37ca96b441bcf255c4361a6b6e1873603a92f3.zip | |
ACPI: Check MSR valid bit before using P-state frequencies
commit 9855d8ce41a7801548a05d844db2f46c3e810166 upstream.
To fix incorrect P-state frequencies which can happen on
some AMD systems f594065faf4f9067c2283a34619fc0714e79a98d
"ACPI: Add fixups for AMD P-state figures"
introduced a quirk to obtain the correct values by reading
from AMD specific MSRs.
This did cause a regression when running a kernel using that
quirk under Xen which does (currently) not pass through MSR
reads to the HW. Instead the guest gets a 0 in return.
And this seems to cause a failure to initialize the ondemand
governour (hard to say for sure as all P-states appear to run
at the same frequency).
While this should also be fixed in the hypervisor (to allow
a guest to read that MSR), this patch is intended to work
around the issue in the meantime. In discussion it turned out
that indeed real HW/BIOSes may choose to not set the valid bit
and thus mark the P-state as invalid. So this could be considered
a fix for broken BIOSes that also works around the issue on Xen.
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | drivers/acpi/processor_perflib.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c index 836bfe069042..53e7ac9403a7 100644 --- a/drivers/acpi/processor_perflib.c +++ b/drivers/acpi/processor_perflib.c @@ -340,6 +340,13 @@ static void amd_fixup_frequency(struct acpi_processor_px *px, int i) if ((boot_cpu_data.x86 == 0x10 && boot_cpu_data.x86_model < 10) || boot_cpu_data.x86 == 0x11) { rdmsr(MSR_AMD_PSTATE_DEF_BASE + index, lo, hi); + /* + * MSR C001_0064+: + * Bit 63: PstateEn. Read-write. If set, the P-state is valid. + */ + if (!(hi & BIT(31))) + return; + fid = lo & 0x3f; did = (lo >> 6) & 7; if (boot_cpu_data.x86 == 0x10) |