[Qemu-devel] [PATCH] virtio-pci: enable bus master for old guests

["Michael S. Tsirkin" <mst@redhat.com>]

commit cc943c36faa192cd4b32af8fe5edb31894017d35
    pci: Use bus master address space for delivering MSI/MSI-X messages
breaks virtio-net for rhel6.[56] x86 guests because they don't
enable bus mastering for virtio PCI devices

Old guests forgot to enable bus mastering, enable it
automatically on DRIVER_OK.

Note: we should either back out the original patch from
stable or apply this one on top.

Cc: qemu-stable@nongnu.org
Reported-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
---
 hw/virtio/virtio-pci.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index ddb5da1..af937d2 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -320,6 +320,8 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
         if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
             !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
             proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
+            memory_region_set_enabled(&proxy->pci_dev.bus_master_enable_region,
+                                      true);
         }
         break;
     case VIRTIO_MSI_CONFIG_VECTOR:
-- 
MST