From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH 2/4] KVM: document memory barriers for kvm->vcpus/kvm->online_vcpus Date: Thu, 30 Jul 2015 13:40:13 +0200 Message-ID: <55BA0D1D.7090002@de.ibm.com> References: <1438176538-26191-1-git-send-email-pbonzini@redhat.com> <1438176538-26191-3-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: mtosatti@redhat.com, srutherford@google.com, rkrcmar@redhat.com To: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Return-path: In-Reply-To: <1438176538-26191-3-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org Am 29.07.2015 um 15:28 schrieb Paolo Bonzini: > Signed-off-by: Paolo Bonzini > --- > include/linux/kvm_host.h | 4 ++++ > virt/kvm/kvm_main.c | 2 ++ > 2 files changed, 6 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index bd1097a95704..81089cf1f0c1 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -427,6 +427,10 @@ struct kvm { > > static inline struct kvm_vcpu *kvm_get_vcpu(struct kvm *kvm, int i) > { > + /* 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(); Hmmm, wouldnt something like smp_mb__after_atomic > return kvm->vcpus[i]; > } > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 8dc4828f623f..093b3d10b411 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -2206,6 +2206,8 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) > } > > kvm->vcpus[atomic_read(&kvm->online_vcpus)] = vcpu; and smp_mb__before_atomic be the better function? > + > + /* Pairs with smp_rmb() in kvm_get_vcpu. */ > smp_wmb(); > atomic_inc(&kvm->online_vcpus); >