vhost: Add Shadow VirtQueue kick forwarding capabilities

At this mode no buffer forwarding will be performed in SVQ mode: Qemu
will just forward the guest's kicks to the device.

Host memory notifiers regions are left out for simplicity, and they will
not be addressed in this series.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index c1db02c53e..e5da907b8e 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -11,6 +11,59 @@
 #include "hw/virtio/vhost-shadow-virtqueue.h"
 
 #include "qemu/error-report.h"
+#include "qemu/main-loop.h"
+#include "linux-headers/linux/vhost.h"
+
+/**
+ * Forward guest notifications.
+ *
+ * @n: guest kick event notifier, the one that guest set to notify svq.
+ */
+static void vhost_handle_guest_kick(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, svq_kick);
+    event_notifier_test_and_clear(n);
+    event_notifier_set(&svq->hdev_kick);
+}
+
+/**
+ * Set a new file descriptor for the guest to kick the SVQ and notify for avail
+ *
+ * @svq: The svq
+ * @svq_kick_fd: The svq kick fd
+ *
+ * Note that the SVQ will never close the old file descriptor.
+ */
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
+{
+    EventNotifier *svq_kick = &svq->svq_kick;
+    bool poll_stop = VHOST_FILE_UNBIND != event_notifier_get_fd(svq_kick);
+    bool poll_start = svq_kick_fd != VHOST_FILE_UNBIND;
+
+    if (poll_stop) {
+        event_notifier_set_handler(svq_kick, NULL);
+    }
+
+    /*
+     * event_notifier_set_handler already checks for guest's notifications if
+     * they arrive at the new file descriptor in the switch, so there is no
+     * need to explicitly check for them.
+     */
+    if (poll_start) {
+        event_notifier_init_fd(svq_kick, svq_kick_fd);
+        event_notifier_set(svq_kick);
+        event_notifier_set_handler(svq_kick, vhost_handle_guest_kick);
+    }
+}
+
+/**
+ * Stop the shadow virtqueue operation.
+ * @svq: Shadow Virtqueue
+ */
+void vhost_svq_stop(VhostShadowVirtqueue *svq)
+{
+    event_notifier_set_handler(&svq->svq_kick, NULL);
+}
 
 /**
  * Creates vhost shadow virtqueue, and instructs the vhost device to use the
@@ -39,6 +92,7 @@ VhostShadowVirtqueue *vhost_svq_new(void)
         goto err_init_hdev_call;
     }
 
+    event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
     return g_steal_pointer(&svq);
 
 err_init_hdev_call:
@@ -56,6 +110,7 @@ err_init_hdev_kick:
 void vhost_svq_free(gpointer pvq)
 {
     VhostShadowVirtqueue *vq = pvq;
+    vhost_svq_stop(vq);
     event_notifier_cleanup(&vq->hdev_kick);
     event_notifier_cleanup(&vq->hdev_call);
     g_free(vq);