Re: [Qemu-devel] [PATCH] virtio-pci: enable bus master for old guests

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 09/10/2014 08:35 AM, Greg Kurz wrote:
> On Mon, 8 Sep 2014 19:05:02 +0300
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
>> 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
>>
>> Old guests forgot to enable bus mastering, enable it
>> automatically on DRIVER_OK.
>>
>> Note: we should either back out the original patch from
>> stable or apply this one on top.
>>
>> Cc: qemu-stable@nongnu.org
>> Reported-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>> ---
>>  hw/virtio/virtio-pci.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
>> index ddb5da1..af937d2 100644
>> --- a/hw/virtio/virtio-pci.c
>> +++ b/hw/virtio/virtio-pci.c
>> @@ -320,6 +320,8 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
>>          if ((val & VIRTIO_CONFIG_S_DRIVER_OK) &&
>>              !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
>>              proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
>> +            memory_region_set_enabled(&proxy->pci_dev.bus_master_enable_region,
>> +                                      true);
>>          }
>>          break;
>>      case VIRTIO_MSI_CONFIG_VECTOR:
> 
> Cc'ing Alexey for some SLOF and early boot of the ppc64 kernel expertise.

Cc'ing Nikunj - he is SLOF expert.
I cannot comment - I have no idea what VIRTIO_PCI_FLAG_BUS_MASTER_BUG does.

> 
> Michael,
> 
> This was enough to fix virtio-net in the rhel6.5 x86 guest case. Unfortunately,
> this fails for rhel6.5 ppc64 because it is never called... I did some debugging:
> it looks like the guest kernel calls the OF quisece call to flush pending DMA
> and disables bus master on the virtio-blk device (PCI_COMMAND == 0x3). The
> guest then continues to boot and hangs... It appears that waiting for the
> guest to issue VIRTIO_CONFIG_S_DRIVER_OK is not enough. Since we need this for
> MSI to work, I tried the following and it fixes the issue:
> 
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index af937d2..3d72aa8 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -111,9 +111,14 @@ static void virtio_pci_notify(DeviceState *d, uint16_t vector)
>  {
>      VirtIOPCIProxy *proxy = to_virtio_pci_proxy_fast(d);
>  
> -    if (msix_enabled(&proxy->pci_dev))
> +    if (msix_enabled(&proxy->pci_dev)) {
> +        if (!(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) {
> +            proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG;
> +            memory_region_set_enabled(&proxy->pci_dev.bus_master_enable_region,
> +                                      true);
> +        }
>          msix_notify(&proxy->pci_dev, vector);
> -    else {
> +    } else {
>          VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus);
>          pci_set_irq(&proxy->pci_dev, vdev->isr & 1);
>      }
> 
> If this is acceptable, I'll make it a helper and squash it into your patch.
> 
> Thoughts ?
> 


-- 
Alexey