From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: fix kvmclock breakage from timers branch merge Date: Thu, 04 Sep 2014 19:56:35 +0200 Message-ID: <5408A7D3.7090508@redhat.com> References: <1409835487-14371-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: chris.j.arges@canonical.com, kvm@vger.kernel.org, Thomas Gleixner , John Stultz To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1409835487-14371-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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 > Cc: John Stultz > Reported-by: Chris J Arges > Signed-off-by: Paolo Bonzini > --- > 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(>od->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(>od->seq, seq))); > *t = ns; > >