virtio: support setting memory region based host notifier

This patch introduces the support for setting memory region
based host notifiers for virtio device. This is helpful when
using a hardware accelerator for a virtio device, because
hardware heavily depends on the notification, this will allow
the guest driver in the VM to notify the hardware directly.

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio/virtio-pci.c

@@ -1037,6 +1037,27 @@ assign_error:
     return r;
 }
 
+static int virtio_pci_set_host_notifier_mr(DeviceState *d, int n,
+                                           MemoryRegion *mr, bool assign)
+{
+    VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
+    int offset;
+
+    if (n >= VIRTIO_QUEUE_MAX || !virtio_pci_modern(proxy) ||
+        virtio_pci_queue_mem_mult(proxy) != memory_region_size(mr)) {
+        return -1;
+    }
+
+    if (assign) {
+        offset = virtio_pci_queue_mem_mult(proxy) * n;
+        memory_region_add_subregion_overlap(&proxy->notify.mr, offset, mr, 1);
+    } else {
+        memory_region_del_subregion(&proxy->notify.mr, mr);
+    }
+
+    return 0;
+}
+
 static void virtio_pci_vmstate_change(DeviceState *d, bool running)
 {
     VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
@@ -2652,6 +2673,7 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, void *data)
     k->has_extra_state = virtio_pci_has_extra_state;
     k->query_guest_notifiers = virtio_pci_query_guest_notifiers;
     k->set_guest_notifiers = virtio_pci_set_guest_notifiers;
+    k->set_host_notifier_mr = virtio_pci_set_host_notifier_mr;
     k->vmstate_change = virtio_pci_vmstate_change;
     k->pre_plugged = virtio_pci_pre_plugged;
     k->device_plugged = virtio_pci_device_plugged;

hw/virtio/virtio.c

@@ -2454,6 +2454,19 @@ EventNotifier *virtio_queue_get_host_notifier(VirtQueue *vq)
     return &vq->host_notifier;
 }
 
+int virtio_queue_set_host_notifier_mr(VirtIODevice *vdev, int n,
+                                      MemoryRegion *mr, bool assign)
+{
+    BusState *qbus = qdev_get_parent_bus(DEVICE(vdev));
+    VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
+
+    if (k->set_host_notifier_mr) {
+        return k->set_host_notifier_mr(qbus->parent, n, mr, assign);
+    }
+
+    return -1;
+}
+
 void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name)
 {
     g_free(vdev->bus_name);

include/hw/virtio/virtio-bus.h

@@ -52,6 +52,8 @@ typedef struct VirtioBusClass {
     bool (*has_extra_state)(DeviceState *d);
     bool (*query_guest_notifiers)(DeviceState *d);
     int (*set_guest_notifiers)(DeviceState *d, int nvqs, bool assign);
+    int (*set_host_notifier_mr)(DeviceState *d, int n,
+                                MemoryRegion *mr, bool assign);
     void (*vmstate_change)(DeviceState *d, bool running);
     /*
      * Expose the features the transport layer supports before

include/hw/virtio/virtio.h

@@ -239,6 +239,8 @@ void virtio_queue_set_align(VirtIODevice *vdev, int n, int align);
 void virtio_queue_notify(VirtIODevice *vdev, int n);
 uint16_t virtio_queue_vector(VirtIODevice *vdev, int n);
 void virtio_queue_set_vector(VirtIODevice *vdev, int n, uint16_t vector);
+int virtio_queue_set_host_notifier_mr(VirtIODevice *vdev, int n,
+                                      MemoryRegion *mr, bool assign);
 int virtio_set_status(VirtIODevice *vdev, uint8_t val);
 void virtio_reset(void *opaque);
 void virtio_update_irq(VirtIODevice *vdev);