virtio-pci: use generic logic for command access

In practice, guests don't generate config requests
that cross a word boundary, so the logic to
detect command word access is correct because
PCI_COMMAND is 0x4. But depending on this is
tricky, further, it will break with guests
that do try to generate a misaligned access
as we pass it to devices without splitting.

Better to use the generic range_covers_byte for this.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/virtio-pci.c

@@ -27,6 +27,7 @@
 #include "kvm.h"
 #include "blockdev.h"
 #include "virtio-pci.h"
+#include "range.h"
 
 /* from Linux's linux/virtio_pci.h */
 
@@ -516,17 +517,16 @@ static void virtio_write_config(PCIDevice *pci_dev, uint32_t address,
 {
     VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
 
-    if (PCI_COMMAND == address) {
-        if (!(val & PCI_COMMAND_MASTER)) {
-            if (!(proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG)) {
-                virtio_pci_stop_ioeventfd(proxy);
-                virtio_set_status(proxy->vdev,
-                                  proxy->vdev->status & ~VIRTIO_CONFIG_S_DRIVER_OK);
-            }
-        }
+    pci_default_write_config(pci_dev, address, val, len);
+
+    if (range_covers_byte(address, len, PCI_COMMAND) &&
+        !(pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER) &&
+        !(proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG)) {
+        virtio_pci_stop_ioeventfd(proxy);
+        virtio_set_status(proxy->vdev,
+                          proxy->vdev->status & ~VIRTIO_CONFIG_S_DRIVER_OK);
     }
 
-    pci_default_write_config(pci_dev, address, val, len);
     msix_write_config(pci_dev, address, val, len);
 }