On Mon, Mar 13, 2017 at 11:30:05AM +0100, Christoffer Dall wrote: > On Wed, Mar 08, 2017 at 03:44:11PM +0100, Andrew Jones wrote: > > On Wed, Mar 08, 2017 at 06:33:12AM -0800, Christoffer Dall wrote: > > > > static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu) > > > > @@ -621,7 +617,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > > > > > > > > update_vttbr(vcpu->kvm); > > > > > > > > - if (vcpu->arch.power_off || vcpu->arch.pause) > > > > + if (vcpu->arch.power_off || __kvm_request_test(KVM_REQ_VCPU_PAUSE, vcpu)) > > > > vcpu_sleep(vcpu); > > > > > > > > /* > > > > @@ -644,8 +640,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *run) > > > > run->exit_reason = KVM_EXIT_INTR; > > > > } > > > > > > > > + vcpu->mode = IN_GUEST_MODE; > > > > + smp_mb(); /* ensure vcpu->mode is visible to kvm_vcpu_kick */ > > > > > > I think this comment is misleading, because this smp_mb() is really > > > about ensuring that with respect to other CPUs, the write to vcpu->mode > > > is observable before the read of kvm_request_pending below, and the > > > corresponding other barrier is the barrier implied in cmpxchg used by > > > kvm_vcpu_exiting_guest_mode, which gets called by kvm_vcpu_kick(), which > > > is called after __kvm_set_request. > > > > Agreed > > > > Just an adjustment to our conclusion from last week: > > Will Deacon clarified that the cmpxchg doesn't have barrier semantics if > the cmpxchg operation fails. My brain hurts trying to work out if we're > still safe in that case. Thoughts? > OK, I just ran my brain through a blender, and then I grabbed Radim to bounce my thoughts off him first. I think he and I are in agreement that kvm_arch_vcpu_should_kick() should get a read barrier before the cmpxchg. That smp_rmb() would pair with the general barrier that I have poorly commented in the code above. I'll refresh this series in the next couple days, adding that barrier, and some better comments. Thanks, drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
