4.9-stable review patch. If anyone has any objections, please let me know.
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From: Xiaoming Gao gxm.linux.kernel@gmail.com
commit d3878e164dcd3925a237a20e879432400e369172 upstream.
The TSC calibration code uses HPET as reference. The conversion normalizes the delta of two HPET timestamps:
hpetref = ((tshpet1 - tshpet2) * HPET_PERIOD) / 1e6
and then divides the normalized delta of the corresponding TSC timestamps by the result to calulate the TSC frequency.
tscfreq = ((tstsc1 - tstsc2 ) * 1e6) / hpetref
This uses do_div() which takes an u32 as the divisor, which worked so far because the HPET frequency was low enough that 'hpetref' never exceeded 32bit.
On Skylake machines the HPET frequency increased so 'hpetref' can exceed 32bit. do_div() truncates the divisor, which causes the calibration to fail.
Use div64_u64() to avoid the problem.
[ tglx: Fixes whitespace mangled patch and rewrote changelog ]
Signed-off-by: Xiaoming Gao newtongao@tencent.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Cc: peterz@infradead.org Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/38894564-4fc9-b8ec-353f-de702839e44e@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -409,7 +409,7 @@ static unsigned long calc_hpet_ref(u64 d hpet2 -= hpet1; tmp = ((u64)hpet2 * hpet_readl(HPET_PERIOD)); do_div(tmp, 1000000); - do_div(deltatsc, tmp); + deltatsc = div64_u64(deltatsc, tmp);
return (unsigned long) deltatsc; }