Re: [PATCH 4/4] KVM: x86: clean/fix memory barriers in irqchip_in_kernel

[Steve Rutherford]

On Wed, Jul 29, 2015 at 03:28:58PM +0200, Paolo Bonzini wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2d62229aac26..23e47a0b054b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3626,30 +3626,25 @@ long kvm_arch_vm_ioctl(struct file *filp,
>                       r = kvm_ioapic_init(kvm);
>                       if (r) {
>                               mutex_lock(&kvm->slots_lock);
> -                             kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
> -                                                       &vpic->dev_master);
> -                             kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
> -                                                       &vpic->dev_slave);
> -                             kvm_io_bus_unregister_dev(kvm, KVM_PIO_BUS,
> -                                                       &vpic->dev_eclr);
> +                             kvm_destroy_pic(vpic);
>                               mutex_unlock(&kvm->slots_lock);
> -                             kfree(vpic);
>                               goto create_irqchip_unlock;
>                       }
>               } else
>                       goto create_irqchip_unlock;
> -             smp_wmb();
> -             kvm->arch.vpic = vpic;
> -             smp_wmb();
>               r = kvm_setup_default_irq_routing(kvm);
>               if (r) {
>                       mutex_lock(&kvm->slots_lock);
>                       mutex_lock(&kvm->irq_lock);
>                       kvm_ioapic_destroy(kvm);
> -                     kvm_destroy_pic(kvm);
> +                     kvm_destroy_pic(vpic);
>                       mutex_unlock(&kvm->irq_lock);
>                       mutex_unlock(&kvm->slots_lock);
> +                     goto create_irqchip_unlock;
>               }
> +             /* Write kvm->irq_routing before kvm->arch.vpic.  */
> +             smp_wmb();
I assume this pairs with irqchip_in_kernel? 
> +             kvm->arch.vpic = vpic;
>       create_irqchip_unlock:
>               mutex_unlock(&kvm->lock);
>               break;
> -- 
> 1.8.3.1
> 
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