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


From: Nikunj A Dadhania
Subject: Re: [Qemu-devel] [PATCH] virtio-pci: enable bus master for old guests
Date: Wed, 10 Sep 2014 13:44:49 +0530
User-agent: Notmuch/0.17+27~gae47d61 (http://notmuchmail.org) Emacs/24.3.1 (x86_64-redhat-linux-gnu)

Greg Kurz <address@hidden> writes:

> On Mon, 8 Sep 2014 19:05:02 +0300
> "Michael S. Tsirkin" <address@hidden> 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: address@hidden
>> Reported-by: Greg Kurz <address@hidden>
>> Signed-off-by: Jan Kiszka <address@hidden>
>> Signed-off-by: Michael S. Tsirkin <address@hidden>
>> ---
>>  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.
>
> 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).

Getting confused, above you are talking about virtio-net and here it is
virtio-blk.

Anyways, the routines still remains same for both of them.  From SLOF
during init we set DRIVER_OK, and after using the device during the
quiesce, called from linux kernel VIRTIO_CONFIG_S_FAILED is set and then
a VIRTIO_DEVICE_RESET is done.

> 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 ?
>
> -- 
> Gregory Kurz                                     address@hidden
>                                                  address@hidden
> Software Engineer @ IBM/Meiosys                  http://www.ibm.com
> Tel +33 (0)562 165 496
>
> "Anarchy is about taking complete responsibility for yourself."
>         Alan Moore.




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