linux-kernel - [PATCH] x86/tsc: fix 64bit divisor be truncated in calc_hpet

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Date:   Fri, 13 Apr 2018 17:48:08 +0800
From:   Xiaoming Gao <gxm.linux.kernel@...il.com>
To:     x86@...nel.org, linux-kernel@...r.kernel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de, hpa@...or.com
Subject: [PATCH] x86/tsc: fix 64bit divisor be truncated in calc_hpet_ref

 From ba3d2fb699c4d8ee61b05d7e70be48b9c4e22baf Mon Sep 17 00:00:00 2001
From: Xiaoming Gao <newtongao@...cent.com>
Date: Fri, 13 Apr 2018 17:05:18 +0800
Subject: [PATCH] x86/tsc: fix 64bit divisor be truncated in calc_hpet_ref

the HPET frequency got larger on intel skylake, thus could cause tmp to
exceed 32bits.
do_div will truncate 64bits tmp to 32bits, so the frequency calced via
HPET will be wrong, use div64_u64 can fix it.

Signed-off-by: Xiaoming Gao <newtongao@...cent.com>
---
  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 9714a7a..8700269 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -160,7 +160,7 @@ 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;
  }
-- 
1.7.1



View attachment "0001-x86-tsc-fix-64bit-divisor-be-truncated-in-calc_hpet_.patch" of type "text/plain" (1013 bytes)