Re: [PATCH v3 02/24] KVM: x86: new irqchip mode KVM_IRQCHIP_INIT_IN_PROGRESS

["Radim Krčmář" <rkrcmar@redhat.com>]

2017-04-07 10:50+0200, David Hildenbrand:
> Let's add a new mode and set it while we create the irqchip via
> KVM_CREATE_IRQCHIP and KVM_CAP_SPLIT_IRQCHIP.
> 
> This mode will be used later to test if adding routes
> (in kvm_set_routing_entry()) is already allowed.
> 
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> @@ -3934,9 +3934,14 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>  			goto split_irqchip_unlock;
>  		if (kvm->created_vcpus)
>  			goto split_irqchip_unlock;
> +		kvm->arch.irqchip_mode = KVM_IRQCHIP_INIT_IN_PROGRESS;
>  		r = kvm_setup_empty_irq_routing(kvm);
> -		if (r)
> +		if (r) {
> +			kvm->arch.irqchip_mode = KVM_IRQCHIP_NONE;
> +			/* Pairs with smp_rmb() when reading irqchip_mode */
> +			smp_wmb();
>  			goto split_irqchip_unlock;
> +		}
>  		/* Pairs with irqchip_in_kernel. */
>  		smp_wmb();
>  		kvm->arch.irqchip_mode = KVM_IRQCHIP_SPLIT;
> @@ -4024,8 +4029,12 @@ long kvm_arch_vm_ioctl(struct file *filp,
>  			goto create_irqchip_unlock;
>  		}
>  
> +		kvm->arch.irqchip_mode = KVM_IRQCHIP_INIT_IN_PROGRESS;
>  		r = kvm_setup_default_irq_routing(kvm);
>  		if (r) {
> +			kvm->arch.irqchip_mode = KVM_IRQCHIP_NONE;
> +			/* Pairs with smp_rmb() when reading irqchip_mode */
> +			smp_wmb();

I think these two barriers are pointless.

KVM_IRQCHIP_INIT_IN_PROGRESS and KVM_IRQCHIP_NONE have the same result
for readers of irqchip mode and we don't even have a barrier after
setting KVM_IRQCHIP_INIT_IN_PROGRESS mode, so it looks weird.

I can remove them if you agree.

Thanks.