Commit e43c0b2e authored by Michael S. Tsirkin's avatar Michael S. Tsirkin
Browse files

virtio-pci: enable bus master for old guests 



commit cc943c36
    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. For the same reason,
rhel6.[56] ppc64 guests cannot boot on a virtio-blk disk anymore.

Old guests forgot to enable bus mastering, enable it automatically on
DRIVER (guests use some devices before DRIVER_OK).

Reported-by: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: default avatarGreg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
parent 9e8e8c48

hw/virtio/virtio-pci.c

+10 −0
Original line number Diff line number Diff line
@@ -314,6 +314,16 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val) 
            msix_unuse_all_vectors(&proxy->pci_dev);

        }



        /* Linux before 2.6.34 drives the device without enabling

           the PCI device bus master bit. Enable it automatically

           for the guest. This is a PCI spec violation but so is

           initiating DMA with bus master bit clear. */

        if (val == (VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER)) {

            pci_default_write_config(&proxy->pci_dev, PCI_COMMAND,

                                     proxy->pci_dev.config[PCI_COMMAND] |

                                     PCI_COMMAND_MASTER, 1);

        }



        /* Linux before 2.6.34 sets the device as OK without enabling

           the PCI device bus master bit. In this case we need to disable

           some safety checks. */