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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
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@ -314,6 +314,16 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
msix_unuse_all_vectors(&proxy->pci_dev); 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 /* 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 the PCI device bus master bit. In this case we need to disable
some safety checks. */ some safety checks. */