virtio-mem-pci: Device unplug support

Let's support device unplug by forwarding the unplug_request_check()
callback to the virtio-mem device.

Further, disallow changing the requested-size once an unplug request is
pending.

Disallowing requested-size changes handles corner cases such as
(1) pausing the VM (2) requesting device unplug and (3) adjusting the
requested size. If the VM would plug memory (due to the requested size
change) before processing the unplug request, we would be in trouble.

Message-ID: <20230711153445.514112-8-david@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>

1 files changed, 46 insertions, 3 deletions

diff --git a/hw/virtio/virtio-mem-pci.c b/hw/virtio/virtio-mem-pci.c
index 2ef0f07630..c4597e029e 100644
--- a/hw/virtio/virtio-mem-pci.c
+++ b/hw/virtio/virtio-mem-pci.c
@@ -93,12 +93,53 @@ static void virtio_mem_pci_size_change_notify(Notifier *notifier, void *data)
     g_free(qom_path);
 }
 
+static void virtio_mem_pci_unplug_request_check(VirtIOMDPCI *vmd, Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(vmd);
+    VirtIOMEM *vmem = &pci_mem->vdev;
+    VirtIOMEMClass *vpc = VIRTIO_MEM_GET_CLASS(vmem);
+
+    vpc->unplug_request_check(vmem, errp);
+}
+
+static void virtio_mem_pci_get_requested_size(Object *obj, Visitor *v,
+                                              const char *name, void *opaque,
+                                              Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(obj);
+
+    object_property_get(OBJECT(&pci_mem->vdev), name, v, errp);
+}
+
+static void virtio_mem_pci_set_requested_size(Object *obj, Visitor *v,
+                                              const char *name, void *opaque,
+                                              Error **errp)
+{
+    VirtIOMEMPCI *pci_mem = VIRTIO_MEM_PCI(obj);
+    DeviceState *dev = DEVICE(obj);
+
+    /*
+     * If we passed virtio_mem_pci_unplug_request_check(), making sure that
+     * the requested size is 0, don't allow modifying the requested size
+     * anymore, otherwise the VM might end up hotplugging memory before
+     * handling the unplug request.
+     */
+    if (dev->pending_deleted_event) {
+        error_setg(errp, "'%s' cannot be changed if the device is in the"
+                   " process of unplug", name);
+        return;
+    }
+
+    object_property_set(OBJECT(&pci_mem->vdev), name, v, errp);
+}
+
 static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
     VirtioPCIClass *k = VIRTIO_PCI_CLASS(klass);
     PCIDeviceClass *pcidev_k = PCI_DEVICE_CLASS(klass);
     MemoryDeviceClass *mdc = MEMORY_DEVICE_CLASS(klass);
+    VirtIOMDPCIClass *vmdc = VIRTIO_MD_PCI_CLASS(klass);
 
     k->realize = virtio_mem_pci_realize;
     set_bit(DEVICE_CATEGORY_MISC, dc->categories);
@@ -111,6 +152,8 @@ static void virtio_mem_pci_class_init(ObjectClass *klass, void *data)
     mdc->get_memory_region = virtio_mem_pci_get_memory_region;
     mdc->fill_device_info = virtio_mem_pci_fill_device_info;
     mdc->get_min_alignment = virtio_mem_pci_get_min_alignment;
+
+    vmdc->unplug_request_check = virtio_mem_pci_unplug_request_check;
 }
 
 static void virtio_mem_pci_instance_init(Object *obj)
@@ -135,9 +178,9 @@ static void virtio_mem_pci_instance_init(Object *obj)
                               OBJECT(&dev->vdev), VIRTIO_MEM_BLOCK_SIZE_PROP);
     object_property_add_alias(obj, VIRTIO_MEM_SIZE_PROP, OBJECT(&dev->vdev),
                               VIRTIO_MEM_SIZE_PROP);
-    object_property_add_alias(obj, VIRTIO_MEM_REQUESTED_SIZE_PROP,
-                              OBJECT(&dev->vdev),
-                              VIRTIO_MEM_REQUESTED_SIZE_PROP);
+    object_property_add(obj, VIRTIO_MEM_REQUESTED_SIZE_PROP, "size",
+                        virtio_mem_pci_get_requested_size,
+                        virtio_mem_pci_set_requested_size, NULL, NULL);
 }
 
 static const VirtioPCIDeviceTypeInfo virtio_mem_pci_info = {