virtio-pci: Added check for virtio device presence in mm callbacks.

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>
Message-Id: <20210609095843.141378-2-andrew@daynix.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index f1e105fa52..1bef7a2be8 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -1147,6 +1147,10 @@ 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;
@@ -1230,6 +1234,10 @@ 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;