From 08641a24d4e70607f767b066def49d3b3a3f9c98 Mon Sep 17 00:00:00 2001 From: Xiaoming Gao Date: Fri, 13 Apr 2018 17:48:08 +0800 Subject: [PATCH] x86/tsc: Prevent 32bit truncation in calc_hpet_ref() 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 Signed-off-by: Thomas Gleixner 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 --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 47506567435e..183a3a142309 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -316,7 +316,7 @@ static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2) 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; } -- 2.20.1