From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] kvm: x86: Fix kvm clock versioning. Date: Thu, 06 Nov 2014 11:52:22 +0100 Message-ID: <545B52E6.2000503@redhat.com> References: <1415062638-26950-1-git-send-email-osh@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: mtosatti@redhat.com To: Owen Hofmann , kvm@vger.kernel.org Return-path: Received: from mail-wi0-f181.google.com ([209.85.212.181]:62144 "EHLO mail-wi0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750789AbaKFKw1 (ORCPT ); Thu, 6 Nov 2014 05:52:27 -0500 Received: by mail-wi0-f181.google.com with SMTP id n3so1079137wiv.2 for ; Thu, 06 Nov 2014 02:52:26 -0800 (PST) In-Reply-To: <1415062638-26950-1-git-send-email-osh@google.com> Sender: kvm-owner@vger.kernel.org List-ID: On 04/11/2014 01:57, Owen Hofmann wrote: > kvm updates the version number for the guest paravirt clock structure by > incrementing the version of its private copy. It does not read the guest > version, so will write version = 2 in the first update for every new VM, > including after restoring a saved state. If guest state is saved during > reading the clock, it could read and accept struct fields and guest TSC > from two different updates. This changes the code to increment the guest > version and write it back. > > Signed-off-by: Owen Hofmann > --- > arch/x86/kvm/x86.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 0033df3..c25c9d8 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1637,16 +1637,16 @@ static int kvm_guest_time_update(struct kvm_vcpu *v) > vcpu->hv_clock.system_time = kernel_ns + v->kvm->arch.kvmclock_offset; > vcpu->last_guest_tsc = tsc_timestamp; > > + if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time, > + &guest_hv_clock, sizeof(guest_hv_clock)))) > + return 0; > + > /* > * The interface expects us to write an even number signaling that the > * update is finished. Since the guest won't see the intermediate > * state, we just increase by 2 at the end. > */ > - vcpu->hv_clock.version += 2; > - > - if (unlikely(kvm_read_guest_cached(v->kvm, &vcpu->pv_time, > - &guest_hv_clock, sizeof(guest_hv_clock)))) > - return 0; > + vcpu->hv_clock.version = guest_hv_clock.version + 2; > > /* retain PVCLOCK_GUEST_STOPPED if set in guest copy */ > pvclock_flags = (guest_hv_clock.flags & PVCLOCK_GUEST_STOPPED); > Applied, thanks. Paolo