Re: [Qemu-devel] [PATCH v4] vhost-user interrupt management fixes

[Michael S. Tsirkin]

On Thu, Feb 18, 2016 at 12:40:36PM +0200, Victor Kaplansky wrote:
> Since guest_mask_notifier can not be used in vhost-user mode due
> to buffering implied by unix control socket, force
> use_mask_notifier on virtio devices of vhost-user interfaces, and
> send correct callfd to the guest at vhost start.
> 
> Using guest_notifier_mask function in vhost-user case may
> break interrupt mask paradigm, because mask/unmask is not
> really done when returning from guest_notifier_mask call, instead
> message is posted in a unix socket, and processed later.
> 
> Add an option boolean flag 'use_mask_notifier' to disable the use
> of guest_notifier_mask in virtio pci.
> 
> Signed-off-by: Didier Pallard <address@hidden>
> Signed-off-by: Victor Kaplansky <address@hidden>

I still dislike two things here, but I'll apply the bugfix
for now - pls clean it up later.


> ---
> 
> v4 changes:
>  In respond to Michael S. Tsirkin comments:
>    - changed the name of new field to use_guest_notifier_mask
>    - clarified comments
>    - vhost_virtqueue_mask() called for unmask
>    - cosmetic changes
>    - moved the initialization of the new field from virtio_reset
>      to virtio_init.
> 
> v3 changes:
>  In respond to Michael S. Tsirkin comments:
>    - vhost_net.c: removed dependency on virtio-pci.h
>    - vhost.c: simplified the check for vhost-user backend,
>      replaced by checking use_mask_notifier; added comment
>      explaining why vring for vhost-user initialized in
>      unmasked state;
>    - cosmetic fixes.
> 
> v2 changes:
>  - a new boolean field is added to all virtio devices instead
>    of defining a property in some virtio-pci devices.
> 
>  include/hw/virtio/virtio.h |  1 +
>  hw/net/vhost_net.c         | 16 ++++++++++++++--
>  hw/virtio/vhost.c          |  9 +++++++++
>  hw/virtio/virtio-pci.c     | 14 ++++++++------
>  hw/virtio/virtio.c         |  1 +
>  5 files changed, 33 insertions(+), 8 deletions(-)
> 
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 108cdb0f..c38a2fef 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -90,6 +90,7 @@ struct VirtIODevice
>      VMChangeStateEntry *vmstate;
>      char *bus_name;
>      uint8_t device_endian;
> +    bool use_guest_notifier_mask;
>      QLIST_HEAD(, VirtQueue) *vector_queues;
>  };
>  
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 3940a04b..0ca16388 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -306,13 +306,25 @@ int vhost_net_start(VirtIODevice *dev, NetClientState 
> *ncs,
>      }
>  
>      for (j = 0; j < total_queues; j++) {
> +        struct vhost_net *net;
> +
>          r = vhost_net_set_vnet_endian(dev, ncs[j].peer, true);
>          if (r < 0) {
>              goto err_endian;
>          }
> -        vhost_net_set_vq_index(get_vhost_net(ncs[j].peer), j * 2);
> -    }
>  
> +        net = get_vhost_net(ncs[j].peer);
> +        vhost_net_set_vq_index(net, j * 2);
> +
> +        /* Suppress the masking guest notifiers on vhost user
> +         * because vhost user doesn't interrupt masking/unmasking
> +         * properly.
> +         */
> +        if (net->nc->info->type == NET_CLIENT_OPTIONS_KIND_VHOST_USER) {
> +                dev->use_guest_notifier_mask = false;
> +        }

We should move this code and comment to vhost-user where it belongs.


> +     }
> + 
>      r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
>      if (r < 0) {
>          error_report("Error binding guest notifier: %d", -r);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 7dff7554..30467b38 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -855,6 +855,14 @@ static int vhost_virtqueue_start(struct vhost_dev *dev,
>      /* Clear and discard previous events if any. */
>      event_notifier_test_and_clear(&vq->masked_notifier);
>  
> +    /* Init vring in unmasked state, unless guest_notifier_mask
> +     * will do it later.
> +     */
> +    if (!vdev->use_guest_notifier_mask) {
> +        /* TODO: check and handle errors. */
> +        vhost_virtqueue_mask(dev, vdev, idx, false);
> +    }
> +
>      return 0;
>  
>  fail_kick:
> @@ -1148,6 +1156,7 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, 
> VirtIODevice *vdev, int n,
>      struct vhost_vring_file file;
>  
>      if (mask) {
> +        assert(vdev->use_guest_notifier_mask);
>          file.fd = event_notifier_get_fd(&hdev->vqs[index].masked_notifier);
>      } else {
>          file.fd = 
> event_notifier_get_fd(virtio_queue_get_guest_notifier(vvq));
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 5494ff4a..440776c0 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -806,7 +806,7 @@ static int kvm_virtio_pci_vector_use(VirtIOPCIProxy 
> *proxy, int nvqs)
>          /* If guest supports masking, set up irqfd now.
>           * Otherwise, delay until unmasked in the frontend.
>           */
> -        if (k->guest_notifier_mask) {
> +        if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {

It's nasty that we have to check two things.
We should move guest_notifier_mask out from class it seems,
then we can go back to only checking it.

>              ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
>              if (ret < 0) {
>                  kvm_virtio_pci_vq_vector_release(proxy, vector);
> @@ -822,7 +822,7 @@ undo:
>          if (vector >= msix_nr_vectors_allocated(dev)) {
>              continue;
>          }
> -        if (k->guest_notifier_mask) {
> +        if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>              kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
>          }
>          kvm_virtio_pci_vq_vector_release(proxy, vector);
> @@ -849,7 +849,7 @@ static void kvm_virtio_pci_vector_release(VirtIOPCIProxy 
> *proxy, int nvqs)
>          /* If guest supports masking, clean up irqfd now.
>           * Otherwise, it was cleaned when masked in the frontend.
>           */
> -        if (k->guest_notifier_mask) {
> +        if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>              kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
>          }
>          kvm_virtio_pci_vq_vector_release(proxy, vector);
> @@ -882,7 +882,7 @@ static int virtio_pci_vq_vector_unmask(VirtIOPCIProxy 
> *proxy,
>      /* If guest supports masking, irqfd is already setup, unmask it.
>       * Otherwise, set it up now.
>       */
> -    if (k->guest_notifier_mask) {
> +    if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>          k->guest_notifier_mask(vdev, queue_no, false);
>          /* Test after unmasking to avoid losing events. */
>          if (k->guest_notifier_pending &&
> @@ -905,7 +905,7 @@ static void virtio_pci_vq_vector_mask(VirtIOPCIProxy 
> *proxy,
>      /* If guest supports masking, keep irqfd but mask it.
>       * Otherwise, clean it up now.
>       */ 
> -    if (k->guest_notifier_mask) {
> +    if (vdev->use_guest_notifier_mask && k->guest_notifier_mask) {
>          k->guest_notifier_mask(vdev, queue_no, true);
>      } else {
>          kvm_virtio_pci_irqfd_release(proxy, queue_no, vector);
> @@ -1022,7 +1022,9 @@ static int virtio_pci_set_guest_notifier(DeviceState 
> *d, int n, bool assign,
>          event_notifier_cleanup(notifier);
>      }
>  
> -    if (!msix_enabled(&proxy->pci_dev) && vdc->guest_notifier_mask) {
> +    if (!msix_enabled(&proxy->pci_dev) &&
> +        vdev->use_guest_notifier_mask &&
> +        vdc->guest_notifier_mask) {
>          vdc->guest_notifier_mask(vdev, n, !assign);
>      }
>  
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 90f25451..e365960b 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1677,6 +1677,7 @@ void virtio_init(VirtIODevice *vdev, const char *name,
>      vdev->vmstate = qemu_add_vm_change_state_handler(virtio_vmstate_change,
>                                                       vdev);
>      vdev->device_endian = virtio_default_endian();
> +    vdev->use_guest_notifier_mask = true;
>  }
>  
>  hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n)
> -- 
> Victor