Subject: Re: [PATCH 2/2] virtio-net: fix buggy features advertised by host

From: Jason Wang <[email-masked]>
Date: Thu, 13 Nov 2014 17:12:27 +0800

On 11/13/2014 04:53 PM, Cornelia Huck wrote:
> On Thu, 13 Nov 2014 13:52:54 +0800
> Jason Wang <[email-masked]> wrote:
>
>> This patch tries to detect the possible buggy features advertised by host
>> and fix them. One example is booting virtio-net with only ctrl_vq disabled,
>> qemu may still advertise many features which depends on it. This will
>> trigger several BUG()s in virtnet_send_command().
>>
>> This patch utilizes the fix_features() method, and disables all features that
>> depends on ctrl_vq if it was not advertised.
>>
>> This fixes the crash when booting with ctrl_vq=off.
> That's a qemu device property, right? Might want to mention that, as
> this line sounds like it is a kernel parameter.

Right, ok.
>> Cc: Rusty Russell <[email-masked]>
>> Cc: Michael S. Tsirkin <[email-masked]>
>> Signed-off-by: Jason Wang <[email-masked]>
>> ---
>> Changes from V1:
>> - fix the cut-and-paste error
>> ---
>>  drivers/net/virtio_net.c | 35 +++++++++++++++++++++++++++++++++++
>>  1 file changed, 35 insertions(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index ec2a8b4..6ce125e 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -1948,6 +1948,40 @@ static int virtnet_restore(struct virtio_device *vdev)
>>  }
>>  #endif
>>
>> +static void virtnet_fix_features(struct virtio_device *dev)
>> +{
>> +	if (!virtio_has_feature(dev, VIRTIO_NET_F_CTRL_VQ)) {
>> +		if (virtio_has_feature(dev, VIRTIO_NET_F_CTRL_RX)) {
>> +			pr_warning("Disable VIRTIO_NET_F_CTRL_RX since host "
>> +				   "does not advertise VIRTIO_NET_F_CTRL_VQ");
>> +			virtio_disable_feature(dev, VIRTIO_NET_F_CTRL_RX);
>> +		}
> You should probably use dev_warn() or so, so that the user can figure
> out which device the message is for. And perhaps add "buggy hypervisor"
> to the message to make clear that it's not a guest problem.

Ok.
> I also like the suggestion to use a dependency array.
>

Yes, will do it in next version.