[Qemu-devel] [PATCH v5] vhost-user interrupt management fixes

[Victor Kaplansky <victork@redhat.com>]

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 <didier.pallard@6wind.com>
Signed-off-by: Victor Kaplansky <victork@redhat.com>
---
v5 changes:
  - rebased to mst tree.  
  - removed a traling space.

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         | 15 +++++++++++++--
 hw/virtio/vhost.c          |  9 +++++++++
 hw/virtio/virtio-pci.c     | 14 ++++++++------
 hw/virtio/virtio.c         |  1 +
 5 files changed, 32 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 b2428324..6e1032fc 100644
--- a/hw/net/vhost_net.c
+++ b/hw/net/vhost_net.c
@@ -284,8 +284,19 @@ int vhost_net_start(VirtIODevice *dev, NetClientState *ncs,
     }
 
     for (i = 0; i < total_queues; i++) {
-        vhost_net_set_vq_index(get_vhost_net(ncs[i].peer), i * 2);
-    }
+        struct vhost_net *net;
+
+        net = get_vhost_net(ncs[i].peer);
+        vhost_net_set_vq_index(net, i * 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;
+        }
+     }
 
     r = k->set_guest_notifiers(qbus->parent, total_queues * 2, true);
     if (r < 0) {
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 9f8ac38c..72d0c9e9 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -875,6 +875,14 @@ 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:
@@ -1167,6 +1175,7 @@ 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) {
             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