From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH] KVM: x86: update master clock before computing kvmclock_offset Date: Wed, 17 May 2017 02:56:01 -0400 (EDT) Message-ID: <1466623738.8419146.1495004161792.JavaMail.zimbra@redhat.com> References: <20170516205000.5436-1-rkrcmar@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Marcelo Tosatti To: Radim =?utf-8?B?S3LEjW3DocWZ?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:60344 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752850AbdEQG4K (ORCPT ); Wed, 17 May 2017 02:56:10 -0400 In-Reply-To: <20170516205000.5436-1-rkrcmar@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: > I regret not pressing harder when we sanctified this frequency > difference ... too late to make kvm clock follow the boot clock? :) > --- > arch/x86/kvm/x86.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index b54125b590e8..b8aad0969690 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -4180,9 +4180,15 @@ long kvm_arch_vm_ioctl(struct file *filp, > goto out; > > r = 0; > + /* > + * TODO: userspace has to take care of races with VCPU_RUN, so > + * kvm_gen_update_masterclock() can be cut down to locked > + * pvclock_update_vm_gtod_copy(). > + */ > + kvm_gen_update_masterclock(kvm); > now_ns = get_kvmclock_ns(kvm); > kvm->arch.kvmclock_offset += user_ns.clock - now_ns; > - kvm_gen_update_masterclock(kvm); > + kvm_make_all_cpus_request(kvm, KVM_REQ_CLOCK_UPDATE); > break; Looks good, though I'd still prefer to do what the TODO says... I'll try to put together a patch today. Paolo