This is a note to let you know that I've just added the patch titled
ACPI: Check MSR valid bit before using P-state frequencies
to the 3.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
acpi-check-msr-valid-bit-before-using-p-state-frequencies.patch
and it can be found in the queue-3.7 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 9855d8ce41a7801548a05d844db2f46c3e810166 Mon Sep 17 00:00:00 2001
From: Stefan Bader <[email protected]>
Date: Tue, 22 Jan 2013 13:37:21 +0100
Subject: ACPI: Check MSR valid bit before using P-state frequencies
From: Stefan Bader <[email protected]>
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 <[email protected]>
Acked-by: Borislav Petkov <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
drivers/acpi/processor_perflib.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -340,6 +340,13 @@ static void amd_fixup_frequency(struct a
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)
Patches currently in stable-queue which might be from
[email protected] are
queue-3.7/acpi-check-msr-valid-bit-before-using-p-state-frequencies.patch
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