linux-kernel - [PATCH 4.4 42/67] x86/tsc: Read all ratio bits from MSR_PLATFORM

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Message-Id: <20160509071839.344145708@linuxfoundation.org>
Date:	Mon,  9 May 2016 09:18:47 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Chen Yu <yu.c.chen@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Bin Gao <bin.gao@...el.com>, Len Brown <lenb@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 4.4 42/67] x86/tsc: Read all ratio bits from MSR_PLATFORM_INFO

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chen Yu <yu.c.chen@...el.com>

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@...el.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Bin Gao <bin.gao@...el.com>
Cc: Len Brown <lenb@...nel.org>
Link: http://lkml.kernel.org/r/1462505619-5516-1-git-send-email-yu.c.chen@intel.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- 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;