[Qemu-devel] [PATCH] Revert "virtio: move common ioeventfd handling out of virtio-pci"

[Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>]

This reverts commit b1f416aa8d870fab71030abc9401cfc77b948e8e.

The above commit breaks vhost_net because it always registers the
virtio_pci_host_notifier_read() handler function on the ioeventfd, even
when vhost_net.ko is using the ioeventfd.  The result is both QEMU and
vhost_net.ko polling on the same eventfd and the virtio_net.ko guest
driver seeing inconsistent results:

  # ifconfig eth0 192.168.0.1 netmask 255.255.255.0
  virtio_net virtio0: output:id 0 is not a head!

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
---
 hw/virtio-pci.c |   36 ++++++++++++++++++++++++++++++++++--
 hw/virtio.c     |   22 ----------------------
 hw/virtio.h     |    1 -
 3 files changed, 34 insertions(+), 25 deletions(-)

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 3ab9747..34262cb 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -173,18 +173,46 @@ static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
                          __func__, r);
             return r;
         }
-        virtio_queue_set_host_notifier_fd_handler(vq, true);
         memory_region_add_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
                                   true, n, notifier);
     } else {
         memory_region_del_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
                                   true, n, notifier);
-        virtio_queue_set_host_notifier_fd_handler(vq, false);
+        /* Handle the race condition where the guest kicked and we deassigned
+         * before we got around to handling the kick.
+         */
+        if (event_notifier_test_and_clear(notifier)) {
+            virtio_queue_notify_vq(vq);
+        }
+
         event_notifier_cleanup(notifier);
     }
     return r;
 }
 
+static void virtio_pci_host_notifier_read(void *opaque)
+{
+    VirtQueue *vq = opaque;
+    EventNotifier *n = virtio_queue_get_host_notifier(vq);
+    if (event_notifier_test_and_clear(n)) {
+        virtio_queue_notify_vq(vq);
+    }
+}
+
+static void virtio_pci_set_host_notifier_fd_handler(VirtIOPCIProxy *proxy,
+                                                    int n, bool assign)
+{
+    VirtQueue *vq = virtio_get_queue(proxy->vdev, n);
+    EventNotifier *notifier = virtio_queue_get_host_notifier(vq);
+    if (assign) {
+        qemu_set_fd_handler(event_notifier_get_fd(notifier),
+                            virtio_pci_host_notifier_read, NULL, vq);
+    } else {
+        qemu_set_fd_handler(event_notifier_get_fd(notifier),
+                            NULL, NULL, NULL);
+    }
+}
+
 static void virtio_pci_start_ioeventfd(VirtIOPCIProxy *proxy)
 {
     int n, r;
@@ -204,6 +232,8 @@ static void virtio_pci_start_ioeventfd(VirtIOPCIProxy *proxy)
         if (r < 0) {
             goto assign_error;
         }
+
+        virtio_pci_set_host_notifier_fd_handler(proxy, n, true);
     }
     proxy->ioeventfd_started = true;
     return;
@@ -214,6 +244,7 @@ assign_error:
             continue;
         }
 
+        virtio_pci_set_host_notifier_fd_handler(proxy, n, false);
         r = virtio_pci_set_host_notifier_internal(proxy, n, false);
         assert(r >= 0);
     }
@@ -235,6 +266,7 @@ static void virtio_pci_stop_ioeventfd(VirtIOPCIProxy *proxy)
             continue;
         }
 
+        virtio_pci_set_host_notifier_fd_handler(proxy, n, false);
         r = virtio_pci_set_host_notifier_internal(proxy, n, false);
         assert(r >= 0);
     }
diff --git a/hw/virtio.c b/hw/virtio.c
index d146f86..1fab9bb 100644
--- a/hw/virtio.c
+++ b/hw/virtio.c
@@ -1012,28 +1012,6 @@ EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq)
 {
     return &vq->guest_notifier;
 }
-
-static void virtio_queue_host_notifier_read(EventNotifier *n)
-{
-    VirtQueue *vq = container_of(n, VirtQueue, host_notifier);
-    if (event_notifier_test_and_clear(n)) {
-        virtio_queue_notify_vq(vq);
-    }
-}
-
-void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign)
-{
-    if (assign) {
-        event_notifier_set_handler(&vq->host_notifier,
-                                   virtio_queue_host_notifier_read);
-    } else {
-        event_notifier_set_handler(&vq->host_notifier, NULL);
-        /* Test and clear notifier before after disabling event,
-         * in case poll callback didn't have time to run. */
-        virtio_queue_host_notifier_read(&vq->host_notifier);
-    }
-}
-
 EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq)
 {
     return &vq->host_notifier;
diff --git a/hw/virtio.h b/hw/virtio.h
index f8b5535..6ae5b6e 100644
--- a/hw/virtio.h
+++ b/hw/virtio.h
@@ -233,7 +233,6 @@ EventNotifier *virtio_queue_get_guest_notifier(VirtQueue *vq);
 void virtio_queue_set_guest_notifier_fd_handler(VirtQueue *vq, bool assign,
                                                 bool with_irqfd);
 EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq);
-void virtio_queue_set_host_notifier_fd_handler(VirtQueue *vq, bool assign);
 void virtio_queue_notify_vq(VirtQueue *vq);
 void virtio_irq(VirtQueue *vq);
 #endif
-- 
1.7.10.4