linux-kernel - Re: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge

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Date:	Fri, 05 Sep 2014 18:39:49 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	linux-kernel@...r.kernel.org, chris.j.arges@...onical.com,
	kvm@...r.kernel.org, John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge

Il 05/09/2014 17:14, Thomas Gleixner ha scritto:
> So that means the code is correct. Now where is the bug?

In kernel/time/timekeeping.c?

We know that we should have

  base_mono             =     wall_to_monotonic + xtime_sec

Instead it is

  base_mono             = wall_to_monotonic + xtime_sec
                          - seconds from boot time

which is... zero.  Given this is the only use of base_mono in a
notifier, I wonder if it is as simple as this (which I don't have time
to test right now):

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index fb4a9c2cf8d9..f6807a85b8c9 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -443,9 +443,9 @@ static void timekeeping_update(struct timekeeper
*tk, unsigned int action)
 		ntp_clear();
 	}
 	update_vsyscall(tk);
-	update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);

 	tk_update_ktime_data(tk);
+	update_pvclock_gtod(tk, action & TK_CLOCK_WAS_SET);

 	if (action & TK_MIRROR)
 		memcpy(&shadow_timekeeper, &tk_core.timekeeper,

:)

Paolo

> Well hidden and still so obvious that it's even visible through the
> brown paperpag I'm wearing ...

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