ivshmem: use kvm irqfd for msi notifications Use irqfd for improving context switch when notifying the guest. If the host doesn't support kvm irqfd, regular msi notifications are still supported. Note: the ivshmem implementation doesn't allow switching between MSI and IO interrupts, this patch doesn't either. Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>