vfio: Move vfio_reset_handler() into device.c

Pass-through devices of a VM are not necessarily in the same group and
all groups/address_spaces need to be scanned when the machine is
reset. Commit f16f39c3fc97 ("Implement PCI hot reset") introduced a VM
reset handler for this purpose. Move it under device.c

Also reintroduce the comment which explained the context and was lost
along the way.

Reviewed-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
Reviewed-by: John Levon <john.levon@nutanix.com>
Link: https://lore.kernel.org/qemu-devel/20250326075122.1299361-26-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

1 files changed, 35 insertions, 0 deletions

diff --git a/hw/vfio/device.c b/hw/vfio/device.c
index 179c9fb8de..e122c797c2 100644
--- a/hw/vfio/device.c
+++ b/hw/vfio/device.c
@@ -35,6 +35,41 @@ VFIODeviceList vfio_device_list =
     QLIST_HEAD_INITIALIZER(vfio_device_list);
 
 /*
+ * We want to differentiate hot reset of multiple in-use devices vs
+ * hot reset of a single in-use device. VFIO_DEVICE_RESET will already
+ * handle the case of doing hot resets when there is only a single
+ * device per bus. The in-use here refers to how many VFIODevices are
+ * affected. A hot reset that affects multiple devices, but only a
+ * single in-use device, means that we can call it from our bus
+ * ->reset() callback since the extent is effectively a single
+ * device. This allows us to make use of it in the hotplug path. When
+ * there are multiple in-use devices, we can only trigger the hot
+ * reset during a system reset and thus from our reset handler. We
+ * separate _one vs _multi here so that we don't overlap and do a
+ * double reset on the system reset path where both our reset handler
+ * and ->reset() callback are used. Calling _one() will only do a hot
+ * reset for the one in-use devices case, calling _multi() will do
+ * nothing if a _one() would have been sufficient.
+ */
+void vfio_reset_handler(void *opaque)
+{
+    VFIODevice *vbasedev;
+
+    trace_vfio_reset_handler();
+    QLIST_FOREACH(vbasedev, &vfio_device_list, global_next) {
+        if (vbasedev->dev->realized) {
+            vbasedev->ops->vfio_compute_needs_reset(vbasedev);
+        }
+    }
+
+    QLIST_FOREACH(vbasedev, &vfio_device_list, global_next) {
+        if (vbasedev->dev->realized && vbasedev->needs_reset) {
+            vbasedev->ops->vfio_hot_reset_multi(vbasedev);
+        }
+    }
+}
+
+/*
  * Common VFIO interrupt disable
  */
 void vfio_disable_irqindex(VFIODevice *vbasedev, int index)