x86/tsc: Prevent result truncation on 32bit

commit 17f6bac2249356c795339e03a0742cd79be3cab8 upstream.

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 ]

[ tglx: Backport to stable. Due to massive code changes is the upstream
  	commit not applicable anymore. The issue has gone unnoticed in
  	kernels pre 4.19 because the bogus LPJ value gets fixed up in a
  	later stage of early boot, but it still might cause subtle and hard
  	to debug issues between these two points. ]

Fixes: cf7a63ef4e02 ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 74392d9d51e0a799a7f4fcb974a55e7989ed400a..a10481656d8293ec2d92c7b2e6466ab75e0b9ef0 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1343,7 +1343,7 @@ device_initcall(init_tsc_clocksource);
 
 void __init tsc_early_delay_calibrate(void)
 {
-       unsigned long lpj;
+       u64 lpj;
 
        if (!boot_cpu_has(X86_FEATURE_TSC))
                return;
@@ -1355,7 +1355,7 @@ void __init tsc_early_delay_calibrate(void)
        if (!tsc_khz)
                return;
 
-       lpj = tsc_khz * 1000;
+       lpj = (u64)tsc_khz * 1000;
        do_div(lpj, HZ);
        loops_per_jiffy = lpj;
 }