2017-04-25 21:03+0200, David Hildenbrand:
> We needed the lock to avoid racing with creation of the irqchip on x86. As
> kvm_set_irq_routing() calls srcu_synchronize_expedited(), this lock
> might be held for a longer time.
>
> Let's introduce an arch specific callback to check if we can actually
> add irq routes. For x86, all we have to do is check if we have an
> irqchip in the kernel. We don't need kvm->lock at that point as the
> irqchip is marked as inititalized only when actually fully created.
>
> Reported-by: Steve Rutherford <srutherford@xxxxxxxxxx>
> Fixes: 1df6ddede10a ("KVM: x86: race between KVM_SET_GSI_ROUTING and KVM_CREATE_IRQCHIP")
> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
> ---
> 6 files changed, 18 insertions(+), 21 deletions(-)
Nice!
Reviewed-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> @@ -504,6 +504,7 @@ void vcpu_put(struct kvm_vcpu *vcpu);
> #ifdef __KVM_HAVE_IOAPIC
> void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm);
> void kvm_arch_post_irq_routing_update(struct kvm *kvm);
> +bool kvm_arch_can_set_irq_routing(struct kvm *kvm);
(A nitpick: it might be useful even without __KVM_HAVE_IOAPIC so weak
linking would probably be cleaner for a slow path.)
> #else
> static inline void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm)
> {
> @@ -511,6 +512,10 @@ static inline void kvm_arch_post_irq_ack_notifier_list_update(struct kvm *kvm)
> static inline void kvm_arch_post_irq_routing_update(struct kvm *kvm)
> {
> }
> +static bool kvm_arch_can_set_irq_routing(struct kvm *kvm)
> +{
> + return true;
> +}
> #endif
>
