From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Len Brown , Thomas Gleixner , peterz@infradead.org, Bin Gao Subject: [PATCH 4.14 40/89] x86/tsc: Future-proof native_calibrate_tsc() Date: Mon, 22 Jan 2018 09:45:20 +0100 Message-Id: <20180122083958.657599898@linuxfoundation.org> In-Reply-To: <20180122083954.683903493@linuxfoundation.org> References: <20180122083954.683903493@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Len Brown commit da4ae6c4a0b8dee5a5377a385545d2250fa8cddb upstream. If the crystal frequency cannot be determined via CPUID(15).crystal_khz or the built-in table then native_calibrate_tsc() will still set the X86_FEATURE_TSC_KNOWN_FREQ flag which prevents the refined TSC calibration. As a consequence such systems use cpu_khz for the TSC frequency which is incorrect when cpu_khz != tsc_khz resulting in time drift. Return early when the crystal frequency cannot be retrieved without setting the X86_FEATURE_TSC_KNOWN_FREQ flag. This ensures that the refined TSC calibration is invoked. [ tglx: Steam-blastered changelog. Sigh ] Fixes: 4ca4df0b7eb0 ("x86/tsc: Mark TSC frequency determined by CPUID as known") Signed-off-by: Len Brown Signed-off-by: Thomas Gleixner Cc: peterz@infradead.org Cc: Bin Gao Link: https://lkml.kernel.org/r/0fe2503aa7d7fc69137141fc705541a78101d2b9.1513920414.git.len.brown@intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/tsc.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -612,6 +612,8 @@ unsigned long native_calibrate_tsc(void) } } + if (crystal_khz == 0) + return 0; /* * TSC frequency determined by CPUID is a "hardware reported" * frequency and is the most accurate one so far we have. This