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virtio-pci: enable bus master for old guests 

commit cc943c36fa
    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: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
master
Michael S. Tsirkin 2014-09-11 18:45:33 +02:00
parent 9e8e8c4865
commit e43c0b2ea5
1 changed files with 10 additions and 0 deletions
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10
hw/virtio/virtio-pci.c
View File

@ -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. */