Patch "x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO" has been added to the 3.14-stable tree

This is a note to let you know that I've just added the patch titled

x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

to the 3.14-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:
x86-tsc-read-all-ratio-bits-from-msr_platform_info.patch
and it can be found in the queue-3.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Chen Yu <[email protected]>
Date: Fri, 6 May 2016 11:33:39 +0800
Subject: x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

From: Chen Yu <[email protected]>

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 ]

---
 arch/x86/kernel/tsc_msr.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -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;

Patches currently in stable-queue which might be from [email protected] are

queue-3.14/x86-tsc-read-all-ratio-bits-from-msr_platform_info.patch