From e43c0b2ea5574efb0bedebf6a7d05916eefeba52 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Thu, 11 Sep 2014 18:45:33 +0200 Subject: virtio-pci: enable bus master for old guests 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 Reviewed-by: Greg Kurz Tested-by: Greg Kurz Signed-off-by: Michael S. Tsirkin --- hw/virtio/virtio-pci.c | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'hw/virtio/virtio-pci.c') diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c index ddb5da181c..a827cd41bf 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. */ -- cgit v1.2.1