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| author | Xiaoming Gao <gxm.linux.kernel@gmail.com> | 2018-04-13 17:48:08 +0800 |
|---|---|---|
| committer | Sasha Levin <alexander.levin@microsoft.com> | 2018-05-22 21:36:35 -0400 |
| commit | 908282e78838069c3858880660759adc965d50b5 (patch) | |
| tree | 800a300c6039738aa3184357e88020db2601a934 | |
| parent | 91c3835434860b674ef45bcbfa4a0ea61e2d9194 (diff) | |
x86/tsc: Prevent 32bit truncation in calc_hpet_ref()
[ Upstream commit d3878e164dcd3925a237a20e879432400e369172 ]
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: Sasha Levin <alexander.levin@microsoft.com>
| -rw-r--r-- | arch/x86/kernel/tsc.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 37bae0d67714..8fdcdbf5f309 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -399,7 +399,7 @@ 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; } |