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x86/tsc: Prevent result truncation on 32bit 

Loops per jiffy is calculated by multiplying tsc_khz with 1e3 and then
dividing it by HZ.

Both tsc_khz and the temporary variable holding the multiplication result
are of type unsigned long, so on 32bit the result is truncated to the lower
32bit.

Use u64 as type for the temporary variable and cast tsc_khz to it before
multiplying.

[ tglx: Massaged changelog and removed pointless braces ]

Fixes: cf7a63ef4e ("x86/tsc: Calibrate tsc only once")
Signed-off-by: Chuanhua Lei <chuanhua.lei@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: yixin.zhu@linux.intel.com
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Tatashin <pasha.tatashin@microsoft.com>
Cc: Rajvi Jingar <rajvi.jingar@intel.com>
Cc: Dou Liyang <douly.fnst@cn.fujitsu.com>
Link: https://lkml.kernel.org/r/1536228203-18701-1-git-send-email-chuanhua.lei@linux.intel.com
This commit is contained in:
Chuanhua Lei 2018-09-06 18:03:23 +08:00 committed by Thomas Gleixner
parent 4331f4d5ad
commit 17f6bac224
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kernel/tsc.c
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@ -1415,7 +1415,7 @@ static bool __init determine_cpu_tsc_frequencies(bool early)
static unsigned long __init get_loops_per_jiffy(void)
{
unsigned long lpj = tsc_khz * KHZ;
u64 lpj = (u64)tsc_khz * KHZ;
do_div(lpj, HZ);
return lpj;