[PATCH v4 4/7] virtio-md-pci: Handle unplug of virtio based memory devices

[David Hildenbrand <david@redhat.com>]

While we fence unplug requests from the outside, the VM can still
trigger unplug of virtio based memory devices, for example, in Linux
doing on a virtio-mem-pci device:
    # echo 0 > /sys/bus/pci/slots/3/power

While doing that is not really expected to work without harming the
guest OS (e.g., removing a virtio-mem device while it still provides
memory), let's make sure that we properly handle it on the QEMU side.

We'll add support for unplugging of virtio-mem devices in some
configurations next.

Tested-by: Mario Casquero <mcasquer@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/virtio/virtio-md-pci.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/virtio-md-pci.c b/hw/virtio/virtio-md-pci.c
index e849c3131d..a22a259e2d 100644
--- a/hw/virtio/virtio-md-pci.c
+++ b/hw/virtio/virtio-md-pci.c
@@ -14,6 +14,7 @@
 #include "hw/virtio/virtio-md-pci.h"
 #include "hw/mem/memory-device.h"
 #include "qapi/error.h"
+#include "qemu/error-report.h"
 
 void virtio_md_pci_pre_plug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
 {
@@ -74,7 +75,27 @@ void virtio_md_pci_unplug_request(VirtIOMDPCI *vmd, MachineState *ms,
 
 void virtio_md_pci_unplug(VirtIOMDPCI *vmd, MachineState *ms, Error **errp)
 {
-    /* We don't support hot unplug of virtio based memory devices */
+    DeviceState *dev = DEVICE(vmd);
+    HotplugHandler *bus_handler = qdev_get_bus_hotplug_handler(dev);
+    MemoryDeviceState *md = MEMORY_DEVICE(vmd);
+    Error *local_err = NULL;
+
+    /* Unplug the memory device while it is still realized. */
+    memory_device_unplug(md, ms);
+
+    if (bus_handler) {
+        hotplug_handler_unplug(bus_handler, dev, &local_err);
+        if (local_err) {
+            /* Not expected to fail ... but still try to recover. */
+            memory_device_plug(md, ms);
+            error_propagate(errp, local_err);
+            return;
+        }
+    } else {
+        /* Very unexpected, but let's just try to do the right thing. */
+        warn_report("Unexpected unplug of virtio based memory device");
+        qdev_unrealize(dev);
+    }
 }
 
 static const TypeInfo virtio_md_pci_info = {
-- 
2.41.0