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. 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 <gk...@linux.vnet.ibm.com>
Reviewed-by: Greg Kurz <gk...@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gk...@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
hw/virtio/virtio-pci.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index ddb5da1..a827cd4 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -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. */
--
MST
