Re: [Qemu-devel] [PATCH] [Also for STABLE-0.12] Don't check for bus master for old guests

[Anthony Liguori]

On 03/16/2010 01:18 PM, Alexander Graf wrote:
> Older Linux guests don't activate the bus master enable bit. So for those we
> can just try to be clever and track if they set the DEVICE_OK bit even though
> bus mastering is still disabled.
>
> Under that condition we can disable the windows safety check. With that logic
> in place both guests should work just fine. Without PCI hotplug breaks
> virtio-net in Linux<  2.6.34 guests.
>
> Signed-off-by: Alexander Graf<address@hidden>
> CC: Michael S. Tsirkin<address@hidden>
>    

Applied.  Thanks.

Regards,

Anthony Liguori
> ---
>   hw/virtio-pci.c |   25 ++++++++++++++++++++++++-
>   1 files changed, 24 insertions(+), 1 deletions(-)
>
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 3594152..4fc4b3c 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -76,6 +76,10 @@
>    * 12 is historical, and due to x86 page size. */
>   #define VIRTIO_PCI_QUEUE_ADDR_SHIFT    12
>
> +/* We can catch some guest bugs inside here so we continue supporting older
> +   guests. */
> +#define VIRTIO_PCI_BUG_BUS_MASTER      (1<<  0)
> +
>   /* QEMU doesn't strictly need write barriers since everything runs in
>    * lock-step.  We'll leave the calls to wmb() in though to make it obvious for
>    * KVM or if kqemu gets SMP support.
> @@ -87,6 +91,7 @@
>   typedef struct {
>       PCIDevice pci_dev;
>       VirtIODevice *vdev;
> +    uint32_t bugs;
>       uint32_t addr;
>       uint32_t class_code;
>       uint32_t nvectors;
> @@ -138,6 +143,13 @@ static int virtio_pci_load_config(void * opaque, QEMUFile 
> *f)
>       if (proxy->vdev->config_vector != VIRTIO_NO_VECTOR) {
>           return msix_vector_use(&proxy->pci_dev, proxy->vdev->config_vector);
>       }
> +
> +    /* Try to find out if the guest has bus master disabled, but is
> +       in ready state. Then we have a buggy guest OS. */
> +    if (!(proxy->vdev->status&  VIRTIO_CONFIG_S_DRIVER_OK)&&
> +        !(proxy->pci_dev.config[PCI_COMMAND]&  PCI_COMMAND_MASTER)) {
> +        proxy->bugs |= VIRTIO_PCI_BUG_BUS_MASTER;
> +    }
>       return 0;
>   }
>
> @@ -162,6 +174,7 @@ static void virtio_pci_reset(DeviceState *d)
>       VirtIOPCIProxy *proxy = container_of(d, VirtIOPCIProxy, pci_dev.qdev);
>       virtio_reset(proxy->vdev);
>       msix_reset(&proxy->pci_dev);
> +    proxy->bugs = 0;
>   }
>
>   static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
> @@ -205,6 +218,14 @@ static void virtio_ioport_write(void *opaque, uint32_t 
> addr, uint32_t val)
>               virtio_reset(proxy->vdev);
>               msix_unuse_all_vectors(&proxy->pci_dev);
>           }
> +
> +        /* 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. */
> +        if ((val&  VIRTIO_CONFIG_S_DRIVER_OK)&&
> +            !(proxy->pci_dev.config[PCI_COMMAND]&  PCI_COMMAND_MASTER)) {
> +            proxy->bugs |= VIRTIO_PCI_BUG_BUS_MASTER;
> +        }
>           break;
>       case VIRTIO_MSI_CONFIG_VECTOR:
>           msix_vector_unuse(&proxy->pci_dev, vdev->config_vector);
> @@ -372,7 +393,9 @@ static void virtio_write_config(PCIDevice *pci_dev, 
> uint32_t address,
>
>       if (PCI_COMMAND == address) {
>           if (!(val&  PCI_COMMAND_MASTER)) {
> -            proxy->vdev->status&= ~VIRTIO_CONFIG_S_DRIVER_OK;
> +            if (!(proxy->bugs&  VIRTIO_PCI_BUG_BUS_MASTER)) {
> +                proxy->vdev->status&= ~VIRTIO_CONFIG_S_DRIVER_OK;
> +            }
>           }
>       }
>
>