From dd458c42c28a36f76df001f5643ef8323ce9b28f Mon Sep 17 00:00:00 2001 From: Chuanhua Lei Date: Thu, 6 Sep 2018 18:03:23 +0800 Subject: [PATCH] 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 Signed-off-by: Thomas Gleixner Cc: yixin.zhu@linux.intel.com Cc: "H. Peter Anvin" Cc: Peter Zijlstra Cc: Len Brown Cc: Pavel Tatashin Cc: Rajvi Jingar Cc: Dou Liyang Link: https://lkml.kernel.org/r/1536228203-18701-1-git-send-email-chuanhua.lei@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/tsc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 74392d9d51e0..a10481656d82 100644 --- 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; }