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    SubjectRe: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge
    Il 04/09/2014 14:58, Paolo Bonzini ha scritto:
    > Commit cbcf2dd3b3d4 (x86: kvm: Make kvm_get_time_and_clockread() nanoseconds
    > based, 2014-07-16) forgot to add tk->xtime_sec, thus breaking kvmclock on
    > hosts that have a reliable TSC. Add it back; and since the field boot_ns
    > is not anymore related to the host boot-based clock, rename boot_ns->nsec_base
    > and the existing nsec_base->snsec_base.
    >
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: John Stultz <john.stultz@linaro.org>
    > Reported-by: Chris J Arges <chris.j.arges@canonical.com>
    > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
    > ---
    > arch/x86/kvm/x86.c | 11 ++++++-----
    > 1 file changed, 6 insertions(+), 5 deletions(-)
    >
    > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    > index 8f1e22d3b286..92493e10937c 100644
    > --- a/arch/x86/kvm/x86.c
    > +++ b/arch/x86/kvm/x86.c
    > @@ -1020,8 +1020,8 @@ struct pvclock_gtod_data {
    > u32 shift;
    > } clock;
    >
    > - u64 boot_ns;
    > u64 nsec_base;
    > + u64 snsec_base;
    > };
    >
    > static struct pvclock_gtod_data pvclock_gtod_data;
    > @@ -1042,8 +1042,9 @@ static void update_pvclock_gtod(struct timekeeper *tk)
    > vdata->clock.mult = tk->tkr.mult;
    > vdata->clock.shift = tk->tkr.shift;
    >
    > - vdata->boot_ns = boot_ns;
    > - vdata->nsec_base = tk->tkr.xtime_nsec;
    > + vdata->nsec_base = tk->xtime_sec * (u64)NSEC_PER_SEC
    > + + boot_ns;
    > + vdata->snsec_base = tk->tkr.xtime_nsec;

    Hmm, I found this comment in kernel/time/timekeeping.c

    /*
    * The xtime based monotonic readout is:
    * nsec = (xtime_sec + wtm_sec) * 1e9 + wtm_nsec + now();
    * The ktime based monotonic readout is:
    * nsec = base_mono + now();

    so this patch makes no sense. The offs_boot part must be broken.

    Paolo

    >
    > write_seqcount_end(&vdata->seq);
    > }
    > @@ -1413,10 +1414,10 @@ static int do_monotonic_boot(s64 *t, cycle_t *cycle_now)
    > do {
    > seq = read_seqcount_begin(&gtod->seq);
    > mode = gtod->clock.vclock_mode;
    > - ns = gtod->nsec_base;
    > + ns = gtod->snsec_base;
    > ns += vgettsc(cycle_now);
    > ns >>= gtod->clock.shift;
    > - ns += gtod->boot_ns;
    > + ns += gtod->nsec_base;
    > } while (unlikely(read_seqcount_retry(&gtod->seq, seq)));
    > *t = ns;
    >
    >



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