[4.2.y-ckt stable] Patch "x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO" has been added to the 4.2.y-ckt tree

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

to the linux-4.2.y-queue branch of the 4.2.y-ckt extended stable tree 
which can be found at:

    https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-4.2.y-queue

This patch is scheduled to be released in version 4.2.8-ckt10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 4.2.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

---8<------------------------------------------------------------

>From df5d9f5ef5bf7062a448a6027ac48bedb92baf06 Mon Sep 17 00:00:00 2001
From: Chen Yu <yu.c.chen at intel.com>
Date: Fri, 6 May 2016 11:33:39 +0800
Subject: x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

commit 886123fb3a8656699dff40afa0573df359abeb18 upstream.

Currently we read the tsc radio: ratio = (MSR_PLATFORM_INFO >> 8) & 0x1f;

Thus we get bit 8-12 of MSR_PLATFORM_INFO, however according to the SDM
(35.5), the ratio bits are bit 8-15.

Ignoring the upper bits can result in an incorrect tsc ratio, which causes the
TSC calibration and the Local APIC timer frequency to be incorrect.

Fix this problem by masking 0xff instead.

[ tglx: Massaged changelog ]

Fixes: 7da7c1561366 "x86, tsc: Add static (MSR) TSC calibration on Intel Atom SoCs"
Signed-off-by: Chen Yu <yu.c.chen at intel.com>
Cc: "Rafael J. Wysocki" <rafael at kernel.org>
Cc: Bin Gao <bin.gao at intel.com>
Cc: Len Brown <lenb at kernel.org>
Link: http://lkml.kernel.org/r/1462505619-5516-1-git-send-email-yu.c.chen@intel.com
Signed-off-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/kernel/tsc_msr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/tsc_msr.c b/arch/x86/kernel/tsc_msr.c
index 92ae6ac..6aa0f4d 100644
--- a/arch/x86/kernel/tsc_msr.c
+++ b/arch/x86/kernel/tsc_msr.c
@@ -92,7 +92,7 @@ unsigned long try_msr_calibrate_tsc(void)

 	if (freq_desc_tables[cpu_index].msr_plat) {
 		rdmsr(MSR_PLATFORM_INFO, lo, hi);
-		ratio = (lo >> 8) & 0x1f;
+		ratio = (lo >> 8) & 0xff;
 	} else {
 		rdmsr(MSR_IA32_PERF_STATUS, lo, hi);
 		ratio = (hi >> 8) & 0x1f;
--
2.7.4