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: b4dc10ba0daa ("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

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 1463468ba9a0a5dc3914c92f88fffb491dc36d4f..6490f618e09696a7a407859037a0b1635cbb6f9f 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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;