During unplug the virtio device is unplugged from virtio-bus on pci. In some cases,
requests to virtio-pci mm may acquire during/after unplug. Added check that virtio
device is on the bus, for "common" memory region.

Signed-off-by: Andrew Melnychenko <andrew@daynix.com>
---
 hw/virtio/virtio-pci.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index b321604d9b..05865b1fcb 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1146,6 +1146,10 @@ static uint64_t virtio_pci_common_read(void *opaque, hwaddr addr,
     uint32_t val = 0;
     int i;
 
+    if (vdev == NULL) {
+        return UINT64_MAX;
+    }
+
     switch (addr) {
     case VIRTIO_PCI_COMMON_DFSELECT:
         val = proxy->dfselect;
@@ -1229,6 +1233,10 @@ static void virtio_pci_common_write(void *opaque, hwaddr addr,
     VirtIOPCIProxy *proxy = opaque;
     VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
 
+    if (vdev == NULL) {
+        return;
+    }
+
     switch (addr) {
     case VIRTIO_PCI_COMMON_DFSELECT:
         proxy->dfselect = val;
-- 
2.31.1