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authorStefan Bader <stefan.bader@canonical.com>2013-01-22 13:37:21 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-01-27 20:49:02 -0800
commit5f37ca96b441bcf255c4361a6b6e1873603a92f3 (patch)
parent709084328e3a553ae6e27f5a8e826baecc3fd615 (diff)
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>
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)