From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753310AbbG3OFx (ORCPT ); Thu, 30 Jul 2015 10:05:53 -0400 Received: from e06smtp16.uk.ibm.com ([195.75.94.112]:44242 "EHLO e06smtp16.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753235AbbG3OFu (ORCPT ); Thu, 30 Jul 2015 10:05:50 -0400 X-Helo: d06dlp02.portsmouth.uk.ibm.com X-MailFrom: borntraeger@de.ibm.com X-RcptTo: linux-kernel@vger.kernel.org Message-ID: <55BA2F3A.8060501@de.ibm.com> Date: Thu, 30 Jul 2015 16:05:46 +0200 From: Christian Borntraeger User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org CC: mtosatti@redhat.com, srutherford@google.com, rkrcmar@redhat.com Subject: Re: [PATCH 2/4] KVM: document memory barriers for kvm->vcpus/kvm->online_vcpus References: <1438176538-26191-1-git-send-email-pbonzini@redhat.com> <1438176538-26191-3-git-send-email-pbonzini@redhat.com> <55BA0D1D.7090002@de.ibm.com> <55BA1C94.80200@redhat.com> <55BA2D2E.7080901@de.ibm.com> <55BA2E68.9030207@redhat.com> In-Reply-To: <55BA2E68.9030207@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15073014-0025-0000-0000-0000063A2408 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 30.07.2015 um 16:02 schrieb Paolo Bonzini: > > > On 30/07/2015 15:57, Christian Borntraeger wrote: >>>>>> + /* Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, in case >>>>>> + * the caller has read kvm->online_vcpus before (as is the case >>>>>> + * for kvm_for_each_vcpu, for example). >>>>>> + */ >> is somewhat distracting because of "read" and "before". So something like >> >> /* Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, to serialize the setting >> of kvm->vcpus and setting kvm->online_vcpus.... >> >> might be better. > > What you are suggesting would go in kvm_vm_ioctl_create_vcpu, e.g. > rewriting: > > /* Pairs with smp_rmb() in kvm_get_vcpu. */ > smp_wmb(); > > like this: > > /* > * Pairs with smp_rmb() in kvm_get_vcpu. Write kvm->vcpus > * before kvm->online_vcpu's incremented value. > */ > smp_wmb(); > > Instead, kvm_get_cpu has: > > /* > * Pairs with smp_wmb() in kvm_vm_ioctl_create_vcpu, in case > * the caller has read kvm->online_vcpus before (as is the case > * for kvm_for_each_vcpu, for example). > */ > smp_rmb(); > > which already describes which loads are serialized here. > > Is this correct? Right you are.