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

Thomas Gleixner
2014-09-05T18:33:22Z

On Fri, 5 Sep 2014, Paolo Bonzini wrote:

> 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);

Why are you moving the update between vsycall and pvclock update as I
did in my patch? We really need to update everything before calling
somewhere.

And yes it is that simple. I instrumented the stuff and its correct
now.

Thanks

tglx