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Date: Fri, 22 Dec 2017 00:27:54 -0500 From: Len Brown <lenb@...nel.org> To: x86@...nel.org Cc: peterz@...radead.org, linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>, Bin Gao <bin.gao@...el.com>, stable@...r.kernel.org Subject: [PATCH 1/3] x86/tsc: Future-proof native_calibrate_tsc() From: Len Brown <len.brown@...el.com> If native_calibrate_tsc() can not discover the TSC frequency, via CPUID or via built-in table, it must return without setting X86_FEATURE_TSC_KNOWN_FREQ. Otherwise, X86_FEATURE_TSC_KNOWN_FREQ will prevent TSC refined calibration. This patch allows Linux to correctly support future Intel hardware, that has (cpu_khz != tsc_khz), and support for CPUID.15 without support for CPUID.15.crystal_khz. This patch is needed since X86_FEATURE_TSC_KNOWN_FREQ was added in Linux-4.10: commit 4ca4df0b7eb0 ("x86/tsc: Mark TSC frequency determined by CPUID as known") If not applied, such systems will run with tsc_khz = cpu_khz, which may result in under-stated TSC rate, and time-of-day drift. Signed-off-by: Len Brown <len.brown@...el.com> Cc: Bin Gao <bin.gao@...el.com> Cc: <stable@...r.kernel.org> # v4.10+ --- arch/x86/kernel/tsc.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 8ea117f8142e..ce4b71119c36 100644 --- 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 -- 2.14.0-rc0
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