Re: [Qemu-devel] [RFC PATCH 18/34] hyperv: add support for KVM_HYPERV_EVENTFD

[Paolo Bonzini <pbonzini@redhat.com>]

On 06/02/2018 21:30, Roman Kagan wrote:
> When setting up a notifier for Hyper-V event connection, attempt to use
> the KVM-assisted one first, and fall back to userspace handling of the
> hypercall if the kernel doesn't provide the requested feature.
> 
> Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>

As before, I wouldn't mind dropping userspace SIGNAL_EVENT altogether.
It would probably end up in bitrot.

Thanks,

Paolo

> ---
>  include/sysemu/kvm.h |  1 +
>  accel/kvm/kvm-all.c  | 15 +++++++++++++++
>  target/i386/hyperv.c | 21 ++++++++++++++++++++-
>  3 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index bbf12a1723..70ad0a54b7 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -496,6 +496,7 @@ void kvm_irqchip_set_qemuirq_gsi(KVMState *s, qemu_irq irq, int gsi);
>  void kvm_pc_gsi_handler(void *opaque, int n, int level);
>  void kvm_pc_setup_irq_routing(bool pci_enabled);
>  void kvm_init_irq_routing(KVMState *s);
> +int kvm_set_hv_event_notifier(KVMState *s, uint32_t conn_id, EventNotifier *n);
>  
>  /**
>   * kvm_arch_irqchip_create:
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index f290f487a5..c3ba87b701 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -1423,6 +1423,21 @@ static void kvm_irqchip_create(MachineState *machine, KVMState *s)
>      s->gsimap = g_hash_table_new(g_direct_hash, g_direct_equal);
>  }
>  
> +int kvm_set_hv_event_notifier(KVMState *s, uint32_t conn_id, EventNotifier *n)
> +{
> +    struct kvm_hyperv_eventfd hvevfd = {
> +        .conn_id = conn_id,
> +        .fd = n ? event_notifier_get_fd(n) : -1,
> +        .flags = n ? 0 : KVM_HYPERV_EVENTFD_DEASSIGN,
> +    };
> +
> +    if (!kvm_check_extension(s, KVM_CAP_HYPERV_EVENTFD)) {
> +        return -ENOSYS;
> +    }
> +
> +    return kvm_vm_ioctl(s, KVM_HYPERV_EVENTFD, &hvevfd);
> +}
> +
>  /* Find number of supported CPUs using the recommended
>   * procedure from the kernel API documentation to cope with
>   * older kernels that may be missing capabilities.
> diff --git a/target/i386/hyperv.c b/target/i386/hyperv.c
> index e43cbb9322..63dcb23fa8 100644
> --- a/target/i386/hyperv.c
> +++ b/target/i386/hyperv.c
> @@ -313,7 +313,8 @@ unlock:
>      return ret;
>  }
>  
> -int hyperv_set_evt_notifier(uint32_t conn_id, EventNotifier *notifier)
> +static int hyperv_set_evt_notifier_userspace(uint32_t conn_id,
> +                                             EventNotifier *notifier)
>  {
>      int ret;
>      EvtHandler *eh;
> @@ -346,6 +347,24 @@ unlock:
>      return ret;
>  }
>  
> +static bool hv_evt_notifier_userspace;
> +
> +int hyperv_set_evt_notifier(uint32_t conn_id, EventNotifier *notifier)
> +{
> +    if (!hv_evt_notifier_userspace) {
> +        int ret = kvm_set_hv_event_notifier(kvm_state, conn_id, notifier);
> +        if (ret != -ENOSYS) {
> +            return ret;
> +        }
> +
> +        hv_evt_notifier_userspace = true;
> +        warn_report("Hyper-V event signaling in KVM not supported; "
> +                    "using slower userspace hypercall processing");
> +    }
> +
> +    return hyperv_set_evt_notifier_userspace(conn_id, notifier);
> +}
> +
>  static uint64_t hvcall_post_message(uint64_t param, bool fast)
>  {
>      uint64_t ret;
>